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Bacterial meningitis


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Bacterial meningitis is an inflammation of the meninges, including the pia, arachnoid, and subarachnoid space, that occurs in response to infection with bacteria and/or bacterial products. Bacterial meningitis is a significant cause of mortality and morbidity worldwide, with considerable variation in incidence depending on age and geographical location of the patient and the causative agent. Young children are at highest risk for mortality and morbidity, especially those from lower socioeconomic strata in countries with poor medical infrastructure, and those infected with Neisseria meningitidis (the meningococcus) or Streptococcus pneumoniae (the pneumococcus). Additional risk factors for poor prognosis after infection include the severity/stage of illness on presentation, exposure to an antibiotic resistant-organism, and the fact that medical professionals lack understanding of mechanisms underlying the pathological features of meningitis. When bacterial meningitis is suspected, immediate action is imperative to establish a definitive diagnosis, and antimicrobial treatment must be initiated immediately as a precautionary measure, because the mortality rate for untreated bacterial meningitis approaches 100%; even with optimal treatment, mortality and morbidity remains high. Neurological sequelae are relatively common in meningitis survivors, especially if the agent of disease is a pneumococcal microorganism. Most pathogenic microbes could potentially cause meningitis in the human brain; however, only two pathogens, N. meningitidis and S. pneumoniae, account for most cases of acute bacterial meningitis, when patients in all age groups are considered. In contrast, in very young children and neonates, most cases are caused by group B streptococcus, Escherichia coli, and Listeria monocytogenes. In developing countries, Haemophilus influenza type b and Salmonella species are still major causes of meningitis in infants and young children. Salmonella meningitis has a particularly dismal prognosis. Meningitis is, in the majority of the cases, a consequence of a preceding bacteremia with encapsulated strains. Although the reasons for this association are incompletely understood, bacterial agents that cause meningitis tend to express a surface structures mimicking structures and epitopes on human cells and, the a antiphagocytic capsule with antiphagocytic properties, that protects them from phagocytosis and normal immune surveillance. Thus, the absence of opsonic or bactericidal antibodies is considered a major risk factor for meningitis. In this regard, age-related incidence of meningococcal and pneumococcal disease is inversely related to prevalence of serum bactericidal activity. Successful identification of microbial epitopes that induce opsonic or bactericidal antibodies and successful vaccination of infants and children using antigenic agents based on these epitopes has changed the epidemiology of bacterial meningitis, particularly due to reduced incidence of Haemophilus influenzae type b-induced meningitis particularlymore so in industrialized countries. However, antigenic epitopes suitable for this preventive approach have not been identified in all organisms that cause meningitis with significant frequency today.
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18 Meningitis
Tone Tønjum
.Petter Brandtzæg
.Birgitta Henriques-Normark
Centre for Molecular Biology and Neuroscience (CMBN), Department of Microbiology, University of
Oslo, Oslo University Hospital, Oslo, Norway
Department of Pediatrics, Ulleva
˚l University Hospital, University of Oslo, Oslo, Norway
Department of Microbiology, Tumor, and Cell Biology, Karolinska Institutet, Stockholm, Sweden
Major Causes of Bacterial Meningitis . . . . . . . . . ........... 402
Neisseria meningitidis and Meningococcal Disease . . . . . . 403
Streptococcus pneumoniae and Pneumococcal
Disease . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
Pathogenesis of Meningococcal and Pneumococcal
Meningitis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 405
Meningococcal and Pneumococcal Colonization and
Carriage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 405
Invasive Meningococcal and Pneumococcal Disease . . . . 408
Meningococcal Cell Structure and Virulence Factors . . . 408
Meningococcal Genome Characteristics and
Dynamics . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
Pathogenesis ............................................... 410
Pathogenesis of Meningococcal Meningitis . . . . . . . . . . . . . 410
Pathogenesis of Pneumococcal Meningitis . . . . . . . . . . . . . . 411
Clinical Features . . . . . . . . . ..................................412
Diagnosis . . . ...............................................414
Laboratory Diagnosis of Meningitis . . . . . . . . . . . . . . . . . . . . . 414
Molecular Typing of N. meningitidis . . . . . . . . . . . . . . . . . . . 416
Molecular Typing of S.pneumoniae .....................416
Host Susceptibility to Meningococcal
and Pneumococcal Meningitis . . . . . . . . . . . . . . . . . . . . . . . . . . 417
Therapy and Management . . . . . . . . . . . . .....................418
Antimicrobial Treatment of Meningococcal
and Pneumococcal Meningitis . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Adjunctive Treatment . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Prevention of Meningococcal and Pneumococcal
Disease . . . . . . ............................................... 419
Chemoprophylaxis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Future Challenges and Opportunities .....................421
Bacterial meningitis is an inflammation of the meninges, includ-
ing the pia, arachnoid, and subarachnoid space, that occurs in
response to infection with bacteria and/or bacterial products.
Bacterial meningitis is a significant cause of mortality and mor-
bidity worldwide, with considerable variation in incidence
depending on age and geographic location of the patient and
the causative agent. Young children are at highest risk for mor-
tality and morbidity, especially those from lower socioeconomic
strata in countries with poor medical infrastructure and those
infected with Neisseria meningitidis (the meningococcus) or
Streptococcus pneumoniae (the pneumococcus). Additional risk
factors for poor prognosis after infection include the severity/
stage of illness on presentation, exposure to an antibiotic-
resistant organism, and the fact that medical professionals lack
understanding of mechanisms underlying the pathological fea-
tures of meningitis. When bacterial meningitis is suspected,
immediate action is imperative to establish a definitive diagno-
sis, and antimicrobial treatment must be initiated immediately
as a precautionary measure, because the mortality rate for
untreated bacterial meningitis approaches 100 %; even with
optimal treatment, mortality and morbidity remain high. Neu-
rological sequelae are relatively common in meningitis survi-
vors, especially if the agent of disease is a pneumococcal
Most pathogenic microbes could potentially cause meningi-
tis in the human brain; however, only two pathogens, N.
meningitidis and S.pneumoniae, account for most cases of
acute bacterial meningitis, when patients in all age groups are
considered. In contrast, in very young children and neonates,
most cases are caused by group B streptococcus, Escherichia coli,
and Listeria monocytogenes. In developing countries,
Haemophilus influenza type b and Salmonella species are still
major causes of meningitis in infants and young children. Sal-
monella meningitis has a particularly dismal prognosis. Menin-
gitis is, in the majority of the cases, a consequence of a preceding
bacteremia with encapsulated strains. Although the reasons for
this association are incompletely understood, bacterial agents
that cause meningitis tend to express surface structures mim-
icking structures and epitopes on human cells and a capsule with
antiphagocytic properties that protect them from phagocytosis
and normal immune surveillance. Thus, the absence of opsonic
or bactericidal antibodies is considered a major risk factor for
meningitis. In this regard, age-related incidence of meningococ-
cal and pneumococcal disease is inversely related to prevalence
of serum bactericidal activity. Successful identification of micro-
bial epitopes that induce opsonic or bactericidal antibodies and
successful vaccination of infants and children using antigenic
agents based on these epitopes has changed the epidemiology of
bacterial meningitis, particularly due to reduced incidence of
Haemophilus influenzae type b-induced meningitis more so in
industrialized countries. However, antigenic epitopes suitable
E. Rosenberg et al. (eds.), The Prokaryotes – Human Microbiology, DOI 10.1007/978-3-642-30144-5_106,
#Springer-Verlag Berlin Heidelberg 2013
for this preventive approach have not been identified in all
organisms that cause meningitis with significant frequency
Major Causes of Bacterial Meningitis
Bacterial meningitis, an inflammation of the meninges affecting
the pia, arachnoid, and subarachnoid space in response to
bacteria and bacterial products, continues to be an important
cause of mortality and morbidity worldwide (WHO 2012).
However, mortality and morbidity vary by age and geographic
location of the patient and the causative organism. Patients
at risk for high mortality and morbidity include infants
and young children, those living in low-income countries
[or in low socioeconomic strata], HIV-infected patients in
developing countries, those infected with Neisseria meningitidis
(the meningococcus, Mc) or Streptococcus pneumoniae
(the pneumococcus, Pc), and infants living in resource-poor
countries infected with Salmonella species (Chang et al. 2004;
Davidsen et al. 2007; Molyneux et al. 2006). In the pre-vaccine
era, Haemophilus influenzae was the most common bacterial
pathogen causing meningitis in young children, and
H.influenzae type b caused approximately 70 % of bacterial
meningitis in children younger than 5 years of age (Dery and
Hasbun 2007). However, in the early 1990s, a conjugated vaccine
against H.influenzae type b was developed, and after a program
to vaccinate against H.influenza type b was implemented, the
global incidence of H.influenzae-induced meningitis decreased
dramatically (55 % reduction in the annual number of cases
in the United States alone) (Thigpen et al. 2011). Subsequently,
S.pneumoniae and N.meningitidis have emerged as the
pathogens responsible for most cases of bacterial meningitis
(Dery and Hasbun 2007; Brouwer et al. 2010).
Almost all microbes that are pathogenic to human beings
have the potential to cause meningitis, but a relatively small
number of pathogens (primarily N.meningitidis,S.pneumoniae,
H.influenzae type b, group B streptococcal disease, Escherichia
coli,Salmonella species, and Listeria monocytogenes) account
for most cases of acute bacterial meningitis in children and
neonates, although the reasons for this remain incompletely
understood (>Table 18.1). One common denominator among
bacterial agents that cause meningitis is the presence of an
antiphagocytic capsule and the related fact that opsonic or
bactericidal antibody is absent in most cases of meningitis
(Gotschlich et al. 1969). As a correlate, age-related incidence
of N.meningitidis,S.pneumoniae, and H.influenzae type b
disease is inversely related to prevalence of serum bactericidal
activity/antibodies (Gotschlich et al. 1969; Chudwin et al. 1983),
and the lack of type-specific antibody is a major risk factor for
neonatal group B streptococcal disease (Baker and Kasper 1976).
Successful identification of microbial epitopes that induce
opsonic or bactericidal antibodies and successful vaccination
of infants and children using antigenic compounds based
on these epitopes have changed the epidemiology of bacterial
meningitis (Peltola 2000; Whitney et al. 2003; Borrow and
Miller 2006; Tsai et al. 2008). However, antigenic epitopes suit-
able for this preventive approach have not been identified for all
organisms that cause meningitis with significant frequency.
Currently, the most agents that cause severe meningitis most
frequently in all age groups worldwide are N.meningitidis and
S.pneumoniae. This chapter reviews the extensive knowledge
base, accumulated over many years by many researchers,
on these organisms and their pathological effects on their
human host.
.Table 18.1
Meningococcal virulence factors
Virulence factor Function
Lipooligosaccharide (LOS) has endotoxin
activity and is released as bacterial outer
membrane vesicles (blebs) or through
cellular lysis. LOS is responsible for toxic
damage to the human tissue, development
of septic shock, and disseminated
intravascular coagulation (DIC) through
interactions with Toll-like receptors (TLR4)
and cytokine induction
Polysaccharide surface component which
works as a protective shell and blocks the
insertion of the membrane attack complex
of the complement system and protects
the bacteria from phagocytosis. The
capsule is the main component enabling
bacterial survival in blood and resisting
bactericidal antibodies. The serogroup
B capsule can also mimic human antigens
Type 4 pili Major adhesins that mediate initial
attachment to nonciliated human cells.
Also required for efficient transformation
of DNA
Outer membrane
proteins (OMP)
Dominant antigens. Porin protein
promotes intracellular survival. Opacity
proteins mediate firm attachment to
eukaryotic cells. Rmp protein can protect
other antigens from bactericidal
interactions with antibodies. Frequent
antigenic variation makes it difficult for the
host immune system to recognize these
Transferrin-, lactoferrin-, and hemoglobin-
binding proteins. Pathogenic Neisseria
spp. are dependent on a constant iron
supply for growth
IgA1 protease Destroys mucosal IgA which is a part of the
local immune system
Beta-lactamase An enzyme that hydrolyzes the b-lactam
ring of penicillin. Important for antibiotic
resistance development
402 18 Meningitis
Neisseria meningitidis and Meningococcal Disease
N.meningitidis, the meningococcus, is a Gram-negative
diplococcus in b-proteobacterium (>Fig. 18.1) that causes
endemic and epidemic meningitis and/or septicemia worldwide.
Epidemic meningococcal meningitis was first described by
Vieusseux in 1805 in Geneva (Vieusseux 1805). Throughout
the nineteenth century, periodic epidemics occurred, involving
primarily young children and adolescents, as well as military
recruits. The genus Neisseria was named after Albert Neisser,
who observed gonococci (Neisseria gonorrhoeae) in leukocytes in
urethral exudates from patients with gonorrhea in 1879.
Marchiafava and Celli (1884) described intracellular oval
micrococci in a sample of cerebrospinal fluid (CSF), and
Anton Weichselbaum (1887) isolated the organism from six
of eight cases of primary sporadic community-acquired
meningitis, identified features that distinguish pneumococci
from meningococci, and gave it the name Diplococcus
intracellularis meningitidis (Marchiafava and Celli 1884;
Weichselbaum 1887). The fact that N.meningitidis enters
human cells is an important feature of meningococcal patho-
genesis. In 1896, Kiefer reported that healthy individuals can be
asymptomatic ‘‘carriers’’ of nasopharyngeal meningococci.
Meningococci are recognized as agents that cause endemic
cases, case clusters, epidemics and pandemics of meningitis,
devastating septicemia, and, less commonly, pneumonia, septic
arthritis, pericarditis, chronic bacteremia, and conjunctivitis in
hundreds of thousands of individuals worldwide each year
(WHO 2012). Mortality can be 10 % or higher in developing
countries, and when patients survive, they often suffer limb loss,
hearing loss, cognitive dysfunction, visual impairment,
educational difficulties, developmental delays, motor nerve
deficits, seizure disorders, and behavioral problems (Kim 2003;
Roine et al. 2008). Curiously, certain geographic and temporal
anomalies exist in the natural history of the disease;
these include the fact that no outbreaks of epidemic
meningococcemia or meningitis prior to 1805 have been
reported, as well as no reported epidemics in the meningitis
belt of sub-Saharan Africa prior to 1900 (Cartwright 1995).
Epidemiology of Meningococcal Disease. Meningococcal
disease is a major global health problem (>Fig. 18.1)
(Stephens 2007) that causes endemic, hyperendemic, epidemic,
and pandemic outbreaks at a rate that varies according to
geographic region, population demographics, host susceptibil-
ity, and infectious agent/strain. In 2010, approximately 170,000
individuals died from meningococcal disease worldwide.
The case fatality rate is 5–10 % in industrialized countries, and
of those who survive, 10–20 % develop permanent sequelae.
Transmission of meningococci occurs by respiratory droplets
or kissing, requiring close contact. They colonize nonciliated
epithelial cells in nasopharynx and the tonsils (Stephens 1982).
Infection, which occurs within 2–10 days, leads to invasive
disease in individuals who lack bactericidal antibodies that
recognize the invading strain and in complement-factor-
deficient individuals (Gotschlich et al. 1969; Stephens et al.
2007). Concurrent viral or mycoplasmal respiratory tract infec-
tions increase susceptibility to systemic invasion by the patho-
genic bacteria.
The meningococcus
Occasional tissue
and dissemination to
and CSF
eal colonization
The pneumococcus
.Fig. 18.1
Stages in microbial CNS pathogenesis. Neisseria meningitidis and Streptococcus pneumoniae are causative agents of meningitis.
Primary adherence to mucosal epithelial cells occurs via pili and other surface components. The bacteria can then establish an intimate
contact with the host cells via outer membrane proteins such as the Opa protein(s), an interaction that might allow bacterial
transcytotic passage to subepithelial tissues. Bacterial interactions with the mucosal cells, submucous tissue and endothelial cells might
result in its entry into the bloodstream and subsequent entry/passage of the blood–brain-barrier to cause meningitis/CNS infection
Meningitis 18 403
The polysaccharide capsule is the primary determinant of
the relative virulence of disease-causing meningococci. Most
infections are caused by strains belonging to serogroups A, B,
C, X, Y, and W-135 (Stephens et al. 2007; Khatami and Pollard
2011). In Western Europe, North America, and South America,
serogroups B and C are the primary disease-causing pathogens,
and these strains are endemic, causing disease at an incidence
of 1–3/100,000. Periodically, local hyperendemic outbreaks
occur when new lineages spread through the population.
In 2001–2006, serogroup B infection spread worldwide,
culminating in disease outbreaks in Australia and New Zealand
(Stephens 2007; Stephens et al. 2007). In China, the Middle East,
and parts of Africa, serogroups A and C predominate.
Large epidemics are attributed predominantly to serogroup
A strains. In the African ‘‘meningitis belt,’’ major periodic
epidemics of serogroup A disease occur every 5–12 years,
with attack rates of 500/100,000 population or higher
(Achtman 1995). The emergence and global importance of
serogroups W-135, X, and Y were recognized only in the last
10 years. Serogroup W-135 was identified in 2002–2003 as
a major threat, and it was the primary pathogen responsible
for outbreaks in Africa. An unprecedented increase in incidence
of serogroup X meningitis was observed in Niger in 2006
(Boisier et al. 2007). Occasionally, particularly virulent strains
arise that cause pandemic outbreaks that manifest across conti-
nents (Stephens et al. 2007). In the USA, Israel, and Sweden,
disease due to serogroup Y strains has increased (Rosenstein
et al. 2001).
Meningococcal disease can occur when a pathogenic organ-
ism infects a susceptible host. Specific factors that increase risk
of meningococcal disease include climate, age, social behavior,
health status including preexisting or coinfection with other
microorganisms (MacLennan et al. 2006), and hereditary factors
(Schneider et al. 2007; Stephens et al. 2007). Additional risk
factors for invasive meningococcal and pneumococcal disease
include smoking, living in crowded conditions, exposure to
pathogen by travel to epidemic areas, deficiency in terminal
complement components, and asplenia (Yazdankhah and
Caugant 2004). Meningococcal and pneumococcal disease can
affect persons of all age groups, but higher rates of invasive
disease in developed countries are seen in infants and children
less than 4 years old, adolescents, military recruits, and individ-
uals living among a transient population (e.g., college students
in dormitories) (Stephens et al. 2007; Rosenstein et al. 2001).
Elderly individuals are also at risk for pneumococcal disease.
Meningococcal serogroup A and C disease increases during the
dry season in Africa. The early stages of disease can mimic a viral
infection such as influenza, but the disease course can be fulmi-
nant. Thus, it can be difficult to identify and treat meningococcal
disease quickly. Rapid progression from bacteremia and/or men-
ingitis to life-threatening septic shock can occur within the first
few hours after initial symptoms appear. Because of these factors,
vaccination is generally the best preventive option for controlling
this disease. Although significant progress has been made in
understanding meningococcal pathogenesis, and effective
meningococcal vaccines along with strategies for vaccination
are or are soon to be available, there remain many challenges
before it will be possible to optimize and deliver effective preven-
tive and therapeutic approaches for meningococcal disease.
Streptococcus pneumoniae and Pneumococcal
The Gram-positive diplococcus S.pneumoniae (>Fig. 18.1)is
a eubacterium belonging to phylum Firmicutes and order
Lactobacillales.S.pneumoniae is a major cause of mild respira-
tory tract infections (i.e., otitis media and sinusitis) and is also
the worldwide leading cause of the much more severe diseases,
community-acquired pneumonia, septicemia, and meningitis.
Epidemiology of S.pneumoniae. It is estimated that between
1.5 and 2 million people die from pneumococcal infection every
year, a rate similar to mortality from tuberculosis. Young
children, the elderly, and immunocompromised individuals
(i.e., splenectomized individuals, HIV patients, and chronically
ill patients suffering from renal or liver disease, alcoholism,
diabetes mellitus, skull fracture, or cochlear implants) (Biernath
et al. 2006; Weisfelt et al. 2006; Brouwer et al. 2010). Past history
of viral infection, especially influenza A virus (IAV), also
sensitizes the host for pneumococcal infection. Coinfection
with pneumococcal influenza is the most important factor
contributing to increased morbidity and/or mortality from
S.pneumoniae worldwide, even accounting for the severity and
increased mortality associated with the 1918 influenza
pandemic. Based on 156 studies published in 2000, O’Brien
et al. estimated the global burden of pneumococcal disease
in children younger than 5 years of age (2009) as close to
14.5 million serious pneumococcal infections and 826,000
deaths, of which 91,000 were in individuals positive for HIV
(O’Brien et al. 2009). More than 61 % of the deaths occurred in
10 African and Asian countries. On a global level, it was estimated
that infection with S.pneumoniae accounts for approximately
11 % of mortality in this age group, when deaths due to infection
with HIV were excluded. Europe had the lowest incidence rate,
6 per 100,000, while the highest rate was 38 per 100,000 in Africa.
The incidence of pneumococcal meningitis in the United States
in children and adults decreased from 1.09 per 100,000 in
1998–1999 to 0.81 in 2006–2007, likely reflecting implementation
of a childhood vaccination program in 2000 (see below) (Thigpen
et al. 2011). In children 2–23 months of age, incidence decreased
from 9.68 to 3.67 in year 2006–2007 (Thigpen et al. 2011).
The case fatality rate in patients with pneumococcal menin-
gitis is equally high in developed and undeveloped regions of the
world (Molyneux et al. 2006). In the youngest children, annual
global case fatality for the year 2000 was estimated to be 59 %,
ranging from 29 % in the western Pacific to 73 % in Africa
(O’Brien et al. 2009). In the United States, the mortality rate
in all patients with pneumococcal meningitis was 17.9 %
in 1998–1999 and 14.7 % in 2006–2007, hence not changing
significantly after vaccine introduction (Thigpen et al. 2011).
Moreover, during 2003–2007, according to the Emerging
Infections Programs network in the United States, the case
404 18 Meningitis
fatality rate in pediatric patients was 9.4 % and 17.5 % in the
adult population (Thigpen et al. 2011). The most common
cause of death in patients with pneumococcal meningitis was
cardiorespiratory failure, stroke, status epilepticus, or brain
herniation (Brouwer et al. 2010).
Sequelae in survivors of pneumococcal meningitis are
present in up to 50 % of cases (Weisfelt et al. 2006; Edmond
et al. 2010; Jit 2010). In a meta-analysis of 48 studies of
pneumococcal meningitis in affluent populations, the pooled
prevalence of individual sequelae was 31.7 % (Jit 2010).
The pooled prevalence of hearing loss, seizures, hydrocephalus,
spasticity/paresis, cranial palsies, and visual impairment was
20.9 %, 6.5 %, 6.8 %, 8.7 %, 12.2 %, and 2.4 %, respectively.
However, cerebral infarction was found in one study in 36 % of
adult patients with pneumococcal meningitis (Schut et al. 2012).
Pathogenesis of Meningococcal
and Pneumococcal Meningitis
Experimental animal models indicate that E.coli and
group B streptococcus initially penetrate the brain via the
cerebral vasculature (Ferrieri et al. 1980). The blood–brain
barrier is a structural and functional barrier formed by brain
microvascular endothelial cells (Rubin and Staddon 1999;
Amiry-Moghaddam et al. 2004; Davidsen et al. 2007) that
protects the brain from microbes and toxins in the
blood. However, meningitis-causing pathogens, including
N.meningitidis and S.pneumoniae, cross the blood–brain
barrier as live bacteria (Ring et al. 1998; Hsu et al. 2009).
Meningitis-causing pathogens cross the blood–brain barrier
transcellularly, paracellularly, or by means of infected
phagocytes (the ‘‘Trojan horse’’ mechanism) (Kim 2009;
Coureuil et al. 2012). For most meningitis-causing pathogens,
including E.coli, group B streptococcus, and S.pneumoniae,
transcellular traversal of the blood–brain barrier in infants and
children (Ring et al. 1998; Hsu et al. 2009) is mediated
by physical interaction with a host cell surface receptor
(Unkmeir et al. 2002; Kim 2009). For example, meningococcal
and pneumococcal organisms bind to and invade human brain
microvascular endothelial cells (HBMEC) (Chudwin et al. 1983;
Doulet et al. 2006; Banerjee et al. 2010). The bacterial Opa
and neuraminidase NanA proteins interact with CD48 and
endoplasmin on HBMEC (Cundell et al. 1995). Invasion of
HBMEC by meningococcal organisms also occurs through
other host–pathogen receptors such as the laminin receptor
(Huang and Jong 2009; Orihuela et al. 2009), a cell surface
membrane receptor for the adhesive basement membrane
protein laminin. Ribosomal protein SA is also a cell
surface ligand for various CNS-infecting microorganisms,
including N.meningitidis,S.pneumoniae,H.influenza type b,
dengue virus, adeno-associated virus, Venezuelan equine
encephalitis virus, and prion protein (Orihuela et al. 2009).
It is not currently understood how the same receptor promotes
penetration of different microorganisms into the CNS.
Meningitis-causing pathogens binding to HBMEC via Lmb
(laminin-binding protein), FbsA (fibrinogen-binding protein),
pili, and IagA (via lipoteichoic acid anchoring) (Stephens et al.
2007; Orihuela et al. 2009), but whether these structures are
unique to meningitis pathogens is unclear. In N.meningitidis,
the outer membrane protein Opc binds to fibronectin, thereby
anchoring the bacteria to the integrin a5b1 receptor on the cell
surface (Orihuela et al. 2009). In addition, N.meningitidis pili
bind to CD46 on HBMEC (Johansson et al. 2003), and
lipooligosaccharides contribute to a high degree of bacteremia
and subsequent penetration into the CNS (Plant et al. 2006).
CD46 is also a receptor for measles, adenovirus, and human
herpesvirus 6 (Manchester et al. 2000; Gaggar et al. 2003;
Santoro et al. 2003). S.pneumoniae crosses the blood–brain
barrier partly through interaction between cell-wall phosphor-
ylcholine and the platelet-activating factor receptor (PAFR), as
shown by partial inhibition of pneumococcal invasion of
HBMEC by a PAFR antagonist (Cundell et al. 1995) and delayed
translocation of pneumococci from the lung to the blood
and from the blood to the CSF in PAFR-knockout mice
(Radin et al. 2005).
Of note, the mechanisms involved in microbial invasion of
the blood–brain barrier differ from those involved in the release
of cytokines and chemokines in response to meningitis-causing
pathogens. For example, interleukin-8 is secreted from HBMEC
infected with E.coli K1, but infected non-brain endothelial cells
(i.e., human umbilical vein endothelial cells) do not secrete IL-8,
and IL-8 secretion does not involve the same E.coli proteins that
mediate invasion of HBMEC (Galanakis et al. 2006). In addi-
tion, c-Jun kinases 1 and 2 promote HBMEC invasion by
N.meningitidis, and in this context, the p38 mitogen-activated
protein kinase (MAPK) pathway promotes release of interleu-
kins 6 and 8. These findings suggest that different proteins and
distinct mechanisms mediate penetration of host cells into the
CNS and the inflammatory process, leading to meningitis.
Meningococcal and Pneumococcal Colonization
and Carriage
Meningococci and pneumococci are commensal pathogens
(Yazdankhah and Caugant 2004), and even though they cause
invasive diseases such as septicemia and meningitis, they also
colonize the upper respiratory tract in 60–70 % of healthy
children who attend day-care centers and in approximately
10 % of the general population. In children under 4 years of
age, the carriage rate of meningococci is <5 %, progressively
increasing to a maximum of 20–25 % in the second and third
decades of life. The pathogens colonize the nasopharyngeal
mucosa, subsequently spreading to the lower respiratory tract,
where an acute inflammatory response is evoked, and clinical
symptoms ensue. Meningococci have also been detected in
tonsillar tissues in up to 45 % of patients hospitalized for
tonsillectomy (Sim et al. 2000).
Asymptomatic individuals harboring these pathogens in the
upper respiratory are considered to be carriers for invasive
meningococcal and pneumococcal disease with subsequent
Meningitis 18 405
transmission occurring largely through respiratory droplets and
secretions. The size of the inoculum required for transmission
from one host to another is not known. Individuals harboring N.
meningitidis and S.pneumoniae in the upper respiratory tract
display pathology of variable severity, ranging from local inflam-
mation to invasion of mucosal surfaces, fulminant sepsis, or
focal infection (Apicella 2005). Meningococcal and pneumococ-
cal disease usually occurs 1–14 days after acquisition of the
pathogen (van Deuren et al. 2000). However, in some cases,
the carrier state can persist for months or even years.
The relationship between meningococcal and pneumococcal
carriage and meningococcal and pneumococcal disease has been
studied to some extent, and carriage prevalence has even been
used as a proxy for predicting outbreaks of meningococcal and
pneumococcal disease. For example, carriage of pneumococci
appears to be a risk factor for meningococcal carriage (Ridda
et al. 2010). The important parameter is the rate of acquisition of
hypervirulent meningococci or pneumococci, not the overall
meningococcal and pneumococcal carriage. The probability of
progression to meningococcal or pneumococcal disease declines
very sharply 10–14 days after acquisition of the pathogen.
The extent to which N.meningitidis and S.pneumoniae interact
with other commensals/pathogens that reside in the upper respi-
ratory tract is an important area for future study. Meningococcal
carriage and its consequences are understood in the context of
a dynamic model. Cross-sectional studies of the microbiome in
meningococcal carriers can provide an incomplete ‘‘snapshot’
of the coexisting flora that colonize the nasopharyngeal mucosa,
especially if some flora localize primarily to intracellular or
submucosal tissue in the nasopharynx. With regard to the poly-
saccharide capsule, its role during carriage/transmission is
not well understood. Capsule-deficient strains are carried and
transmitted efficiently, and the ideas that the capsule increases
resistance to desiccation during transit or that it reduces adhe-
siveness are not well supported. It seems likely that the ability to
switch between capsulate and non-capsulate forms confers
adaptive and/or fitness advantage, possibly by increasing
capacity for cell invasion. In this regard, it has been proposed
that propensity for carriage differs in strains expressing different
capsular polysaccharides (i.e., according to serogroups).
Meningococcal carriage induces bactericidal antibodies
within 1–2 weeks after colonization that persist for several
months. Bactericidal antibodies to N.lactamica cross-react
with antigens from various meningococcal serogroups and
serotypes. As carriage of N.lactamica is approximately 4 % by
3 months of age and peaks at 21 % by 18–24 months of age, this
is much higher than carriage of N.meningitidis at this age
(Yazdankhah and Caugant 2004). N.lactamica can protect
against meningococcal disease. Development of invasive menin-
gococcal disease correlates with the absence of bactericidal
antibodies (Goldschneider et al. 1969).
Meningococci express multiple adhesins (i.e., pilus, Opa,
NadA) characterized by an impressive and high degree of allelic
variation, a property that likely reflects their capacity to import
and incorporate genetic information laterally via genetic
transformation in an addition to extensive intragenomic
recombination. Nevertheless, carriage studies suggest that most
individuals are colonized with a single meningococcal strain,
a fact that constrains the opportunity for genetic exchange
between heterologous strains and emphasizes genetic variation
arising by spontaneous mutations and recombination/gene
conversion within a single strain. Meningococcal adhesins in
other commensal Neisseria sp. have not been well studied.
Thus, it is not clear how allelic meningococcal diversity
occurs with such frequency. One possibility is that it reflects
intragenomic recombination in combination with strong
selection of events providing improved fitness. Alternatively,
we may be vastly underestimating the number of carriers who
are colonized by multiple distinct strains of meningococci and
pneumococci or similarly underestimate the size and diversity of
the genetic pool available to meningococci and pneumococci in
the nasopharynx.
Meningococcal and pneumococcal carriage and transmission,
not disease, determine the global variation and composition of the
natural population of these bacterial entities. Conjugate vaccines
against a variety of encapsulated bacteria including serogroup
C meningococci and multiple serotypes of pneumococci have
been a powerful tool towards preventing or reducing the number
of outbreaks of meningococcal and pneumococcal disease,
providing a compelling rationale for continued study of the
biology of the commensal behavior of meningococci. From an
evolutionary perspective, the interactions between meningococci
and pneumococci and the nonpathogenic flora in the human
nasopharynx are key denominators.
Meningococcal Adhesion and Cell Invasion. Adhesion to
human mucosal surfaces is essential for meningococcal survival,
and adhesins are the bacterial proteins that mediate binding to
cell surface receptors on target host cells. Furthermore, adhesin
redundancy is a hallmark of the meningococcus. Recognized
adhesins include pili, PilC, PilQ, Opa, Opc, LOS, factor
H-binding protein, PorA, HrpA, PorB, and NadA (Merz and So
2000; Hill and Virji 2012). Proposed or demonstrated receptors
include platelet-activating factor, CD46, CEACAM1, vitronectin
and a-actinin/integrins, complement receptor 3, laminin, and
the GP96 scavenger receptor (Hill and Virji 2012).
Initial contact of meningococci with nasopharyngeal epithelial
cells is mediated by type IV pili, the receptor for which may be the
I-domain of integrin a-chains or possibly CD46 (Bourdoulous
and Nassif 2006; Doulet et al. 2006). Meningococci proceed to
proliferate on the surface of human nonciliated epithelial cells,
forming small microcolonies at the site of initial attachment.
Capsule blocks close adhesins other than pili and thus may
aid meningococcal transmission from mucosal surfaces.
Attachment can activate two-component regulatory systems,
leading to loss or downregulation of capsule. Close adherence
of meningococci to the host epithelial cells results in the
formation of cortical plaques and leads to the recruitment
of factors ultimately responsible for the formation and extension
of epithelial cell pseudopodia that engulf the meningococcus
(Doulet et al. 2006). Intimate association is mediated by the
bacterial opacity proteins, Opa and Opc with CD66/CEACAMs
and integrins, respectively, on the surface of the epithelial
406 18 Meningitis
cell and is one trigger of meningococcal internalization
(Gray-Owen and Blumberg 2006). However, the roles of
meningococcal adhesins NadA and LOS are less well defined
(Doulet et al. 2006). In this complex process, large molecular
complexes involving the molecular linkers ezrin and moesin
(known as ERM [ezrin–radixin–moesin] proteins) cluster with
integral membrane proteins, including CD44 and intracellular
adhesion molecule (ICAM) 1, followed by formation of cortical
actin polymers (Hoffmann et al. 2001; Lambotin et al. 2005),
which ultimately lead to cortical plaques and cell membrane
protrusions. The latter step requires phosphorylated cortactin.
Consistent with this, some meningococcal mutants that lack
functional LOS demonstrate reduced invasiveness and aberrant
actin polymers/polymerization and fail to recruit and/or
phosphorylate cortactin (Hoffmann et al. 2001).
The next steps of a meningococcal infection include
internalization, intracellular survival, transcytosis through the
basolateral tissues, and dissemination into the bloodstream;
these processes are not yet thoroughly studied or understood.
Intracellular meningococci reside within a membranous vacuole
and are capable of translocating through the epithelial layers
within 18–40 h after internalization. Intracellular survival
requires IgA1 protease, which degrades lysosome-associated
membrane proteins (LAMPs), thus preventing phagosomal
maturation. IgA1 protease induces a dose-dependent T-cell
response, which is mainly a Th1-based proinflammatory
immune response (Tsirpouchtsidis et al. 2002). Meningococci
can replicate intracellularly, by a process that requires
sequestration and utilization of cellular iron through specialized
transport systems. This process involves host factors such as the
hemoglobin-binding receptor (HmbR), transferrin-binding
protein (TbpAB), and lactoferrin-binding protein (LbpAB)
(Perkins-Balding et al. 2004)(
>Fig. 18.2).
Pneumococcal Adhesion and Cell Invasion. Pneumococci are
encased by a capsular polysaccharide which has been recognized
as a sine qua non of virulence. However, several studies have
indicated that high amounts of capsular polysaccharide prevent
attachment to host cells, probably by masking underlying
virulence determinants. Interestingly, the amount of capsule
is substantially reduced upon contact with epithelial cells
(Hammerschmidt et al. 2005). In addition, the virulence factor
pneumolysin plays a significant role in pathogenesis (Paterson
and Mitchell 2006). The pneumococcal outer cell wall is
composed of peptidoglycan, teichoic acid, and lipoteichoic
acid, which differ only in their attachment to the pneumococcal
cell wall, as well as phosphorylcholine. Phosphorylcholine is not
only targeted by the choline-binding domain of choline-binding
proteins but functions itself as an adhesin by recognizing
the platelet-activating factor receptor of host cells (Cundell
et al. 1995). Through genome mining, it has been predicted
that S.pneumoniae has approximately 200 proteins with
a leader peptide (Bergmann and Hammerschmidt 2006).
The leader peptide is recognized by complex secretion machin-
eries known as translocons and is required for protein traversal
across the membranes. SecA is the main factor of the general
secretory pathway, and the ATPase activity of this protein is the
molecular motor of protein translocation across the mem-
branes. Three clusters of pneumococcal surface proteins can be
distinguished by genome analysis: lipoproteins, the choline-
binding protein family, and proteins with lipoteichoic acid
motifs that are covalently anchored in the cell wall after cleavage
by a transpeptidase, which is a sortase. Bioinformatics analysis of
the pneumococcal genomes also indicates the presence of
incomplete biosynthetic pathways, which is consistent with the
inability of this pathogen to carry out respiratory metabolism,
and also explains the high number of ATP-binding cassette
(ABC) transporters produced by S.pneumoniae. In addition to
these predicted surface proteins, nonclassical surface proteins
that lack a classical leader peptide and membrane-anchoring
motifs have been identified on the pneumococcal surface,
contributing to the virulence of pneumococci and other
pathogenic bacteria.
.Fig. 18.2
(a) Petechiae on a man with mild systemic meningococcemia caused by Neisseria meningitidis serogroup B. (b) Large petechiae and small
ecchymoses in a patient with bacteriologically confirmed N.meningitidis infection. (c) An 18-month-old boy with lethal cardiovascular
collapse caused by N.meningitidis serogroup B (Petter Brandtzæg)
Meningitis 18 407
Invasive Meningococcal and Pneumococcal
Invasive Meningococcal Disease and Meningitis. Once infection is
established, organisms enter the bloodstream, cause bacteremia,
cross the blood–brain barrier, and, ultimately, lead to meningi-
tis. In some instances, untreated meningococcal infections
progress rapidly, leading to death within 12–24 h. As discussed
above, the prognosis after a non-immunized individual is
infected is highly variable, ranging from healthy colonization
to serious or fatal clinical disease, and the exact outcome
depends on characteristics of both the infectious agent and
the host. Some of the most important factors that influence
disease outcome are discussed below.
Meningococcal Cell Structure and Virulence
N.meningitidis, like other Gram-negative bacteria, has a cell wall
that consists of two membranes separated by a thin peptidogly-
can layer. The inner cytoplasmic membrane consists of proteins
embedded in a phospholipid bilayer that is impermeable to
hydrophilic compounds. The outer membrane is an asymmet-
rical bilayer composed of phospholipids in the inner leaflet and
lipooligosaccharide (LOS) in the outer leaflet. The LOS renders
the outer membrane relatively resistant to detergents and is
semipermeable due to the presence of protein channels, called
porins. Other surface-exposed outer membrane proteins and
extracellular appendages such as capsular structures and type
IV pili particularly contribute to neisserial survival and virulence
(Meyer et al. 1994; Merz and So 2000). The neisserial outer
membrane continuously sheds vesicles (blebs) that contain
DNA, protein/peptides, and high levels of LOS.
Capsules.Neisseria meningitidis produces a polysaccharide
capsule (text box). On the basis of structural differences in
capsule, meningococci are divided into at least 13 serogroups
(A, B, C, D, 29E, H,I, K, L, W-135, X,Y, and Z). Serogroups A, B,
C, Y, and W-135 cause more than 90 % of meningococcal
disease. Capsular types are normally stable, but strains can
acquire variant alleles of capsule gene (Vogel et al. 2000).
For example, serogroup B can switch to C and vice versa.
The serogroup A capsule contains N-acetyl-mannosamine-1-
phosphate. The capsules of serogroups B, C, Y, and W-135
consist of polymers of N-acetylneuraminic (sialic) acid.
The B-polysaccharide resembles structures present in human
neural tissues, limiting its immunogenicity and vaccine
potential. The carbohydrates can be variably O-acetylated.
The capsule polymers are anchored in the outer membrane
through a 1,2-dipalmitoyl glycerol moiety. Capsule biosynthesis
can vary and is subject to regulation. Isolates from healthy
carriers are frequently unencapsulated due to lack of capsule
gene expression. A substantial proportion of meningococcal
isolates from carriers carry inactivating mutations in or
deletions of capsule genes. Isolates from the bloodstream or
CSF are invariably encapsulated. In addition to capsule,
meningococci are covered with a loosely adherent capsular-like
structure containing high-molecular-weight polyphosphate.
This layer protects against environmental stress (Zhang
et al. 2010).
Pili. Pili are filamentous hairlike fibers consisting of
thousands of protein subunits (pilin, 16–20 kDa) (Tonjum and
Koomey 1997). Meningococci express long (up to 4,300 nm in
length) type IV pili that protrude from the bacterial surface
(>Fig. 18.1). Type IV pili confer bacterial cell-to-cell interac-
tions and twitching motility—a form of locomotion that
requires extension and retraction of the pilus filament
(Henrichsen 1983). Pili are essential for adhesion to epithelial
and endothelial cells adherence of bacteria to human cells and
for DNA transformation (Swanson 1973; Stephens and McGee
1981) and impart tissue tropism (Meyer et al. 1994; Merz and So
2000). Expression of type IV pili is also required for efficient
DNA uptake in transformation (Jyssum and Lie 1965; Sparling
1966; Davidsen and Tonjum 2006; Hamilton and Dillard 2006).
Pili as well as capsule and PorA are expressed during human
infection as documented by skin biopsies (Harrison et al. 2002).
Several proteins required for the assembly, extrusion, and
retraction of meningococcal type IV pili have been identified
(Carbonnelle et al. 2006). These include PilE (Parge et al. 1995),
ComP (Wolfgang et al. 1999), PilQ (Tonjum et al. 1998; Collins
et al. 2004; Assalkhou et al. 2007), lipoproteins PilP
(Balasingham et al. 2007) and PilW (Trindade et al. 2008), the
prepilin peptidase PilD (Strom et al. 1993), the ATPase PilT
(driving pilus retraction) (Wolfgang et al. 1998; Forest et al.
2004), and the adhesin PilC (Rudel et al. 1995).
The main structural constituent of the type IV pilus fiber is
pilin subunit, PilE. During infection, pilins undergo rapid phase
shifts and antigenic variation. PilE is encoded by a single gene;
however, expression of the PilE gene requires unidirectional
donation of coding sequences from multiple silent partial
pilS genes in a process similar to gene conversion. During
this process, an extensive repertoire of antigenic variants of
PilE is generated (Tonjum and Koomey 1997). The frequency
of antigenic pili variation can be as high as 10
. Pilin is
also posttranslationally modified with phosphorylcholine,
phosphoethanolamine, and variable acetylated O-linked glycans
(Power and Jennings 2003; Aas et al. 2006). N.meningitidis
expresses class I or class II pili, which are antigenically and
structurally distinct. Class II pili are encoded by a different pilE
gene that has no silent cassette counterparts.
Surface Proteins. The repertoire of the meningococcal surface
proteins is substantial (Meyer et al. 1994; Merz and So 2000).
Trimeric protein channels (porins) transport low-molecular-
weight nutrients across the outer membrane. N.meningitidis
can express two types of porins simultaneously: PorA and
PorB. PorA (class 1 protein, 44–47 kDa) is variably expressed,
and in some patients, the level of expression is below the
detection limit, implying that the gene is highly repressed,
inactivated by mutation, or that the protein is expressed
but sequestered and/or modified. Antigenic differences in PorA
(and PorB) are used to classify meningococci into serological
subtypes. Meningococcal PorB is equivalent to the gonococcal
408 18 Meningitis
PorB protein and is represented by one of two isoforms, PorB-IA
(class 2 protein, 40–42 kDa) or PorB-IB (class 3 protein,
37–39 kDa) (Meyer et al. 1994; Merz and So 2000).
Meningococci fail to survive unless they express PorA or PorB.
The neisserial RmpM protein (formerly protein III or class 4
protein) forms a complex with and likely stabilizes outer
membrane protein complexes including porins. The protein is
stably expressed by gonococci and meningococci. Its C-terminal
periplasmic region resembles the analogous protein domain in
E.coli OmpA, whose role involves binding peptidoglycan.
RmpM-specific antibodies interfere with the bactericidal
activity of antibodies against other surface antigens, thereby
increasing the risk of infection (Plummer et al. 1993).
Meningococci express opacity (Opa) proteins (20–28 kDa)
(Meyer et al. 1994; Merz and So 2000). Opa proteins are
structurally similar to one another but display considerable
intra- and interstrain variation in surface-exposed regions
and in level of expression. Intrastrain antigenic variation arises
by intragenomic recombination and horizontal gene transfer,
and variants are subject to selective pressure during infection.
High-frequency phase variation is due to translational
frame-shifting involving a pentameric repeat in the opa genes.
By this mechanism, Opa proteins are switched on and off,
independent of one another, enabling simultaneous expression
of multiple proteins (Meyer et al. 1994). The meningococcal
genome contains 3–4 opa genes. Opa proteins play an important
role in promoting adherence to and invasion of eukaryotic cells.
Because Opa proteins are subject to a high degree of phase
and antigenic variation, they have limited usefulness as
targets for vaccine-based interventions. Approximately 70 % of
meningococcal strains express the Opc protein. This protein also
confers colonial opacity and is functionally similar to Opa.
In addition to the aforementioned major outer membrane
proteins, meningococci express >80 other outer membrane
proteins. Among these, the pilus-related secretin complex PilQ
is one of the most abundant, representing approximately 10 % of
the total mass of the outer membrane protein fraction (Tonjum
et al. 1998). The level of expression of PilQ varies under different
growth conditions. Iron-regulated proteins are also expressed on
the surface of meningococci in vivo. Among these, transferrin-
binding proteins (Tbp-1 and Tbp-2) and the lactoferrin-binding
proteins (Lbp) facilitate transport and internalization of iron, an
essential nutrient for sustained infection. Additional conserved
proteins that provide exposed antigenic targets on the bacterial
cell surface include OMP85, NspA, NadA, GNA1870
(factor H-binding protein), and GNA2132 (hypothetical
lipoprotein); these are considered to be viable targets for vaccine
Lipooligosaccharide. Approximately 50 % of the neisserial
surface is covered by lipid-anchored oligosaccharide (LOS).
LOS lack repeating carbohydrate units (O-chain) of enterobac-
terial lipopolysaccharide (LPS). Neisserial LOS is composed of
hexa-acylated lipid A, two KDO molecules, and one or more
carbohydrate chains of 8–12 saccharide units, the core oligosac-
charide. The lipid A anchors LOS in the outer membrane and is
one of the most potent bacterial endotoxins.
The core oligosaccharide of neisserial LOS is divided into
an inner and outer core region. The composition of the
inner core is heterogeneous due to variable substitutions
(phosphoethanolamine, glycine, glucose, O-acetyl groups)
(Kahler et al. 2005), which occur in response to environmental
cues. The outer core is also variable and undergoes
high-frequency phase and antigenic variation due to frequent
targeted mutagenesis during replication of LOS biosynthesis
genes as well as horizontal gene transfer (Kahler and Stephens
1998). A single strain can simultaneously express up to six
related LOS. The terminal structure of neisserial LOS is sialylated
by bacterial sialyltransferase. Gonococci modify LOS using host
sialic acid (CMP-NeuNAc). In contrast, meningococci use an
endogenous source of CMP-NeuNAc. The terminal LOS of
the pathogenic Neisseria spp. often shares epitopes with host
glycolipids (Kahler and Stephens 1998). In this manner,
molecular mimicry is exploited by the pathogens, which gain
the ability to bind to host cell lectin receptors. This limits the
usefulness of LOS as a vaccine target.
Meningococcal LOS initially react with CD14 and
subsequently with TLR4 receptor which is critical to the
innate immune responses to bacterial endotoxins including
meningococcal LOS (Akira and Takeda 2004). Activation of
TLR4 by endotoxin requires association with the accessory
protein MD-2, an N-glycosylated (Viriyakosol et al. 2001)
19–27-kDa protein that is expressed in both a soluble and
a membrane-bound form. Binding of endotoxin LOS to MD-2
in association with TLR4 can lead to dimerization or oligomer-
ization of TLR4 receptors and subsequent cellular activation.
MD-2 directly interacts with lipid A of meningococcal
Peptidoglycan.Neisserial peptidoglycan consists of long
chains of repeated disaccharide units cross-linked via peptide
bridges. In E.coli, peptidoglycans are found covalently linked to
lipoproteins, but this is not thought to occur in meningococci.
Peptidoglycan metabolism involves both lytic and synthetic
enzymes. Initial synthesis is carried out using four penicillin-
binding proteins (PBPs) (Dillard and Hackett 2005), followed by
O-acetylation, which protects against autolysis by endogenous
lytic transglycosylates and host lysozymes. After release,
peptidoglycan fragments activate the innate immune response
through the intracellular NOD1 and NOD2 receptors and
contribute to inflammatory response.
Secreted Factors. The meningococcal genome is predicted to
encode autotransporter, two-partner, and type I and type II
secretion mechanisms (van Ulsen and Tommassen 2006).
The pathogenic Neisseria spp. secrete immunoglobulin
A1 (IgA1) protease. This serine protease directs its own
transport across the outer membrane into the environment.
The enzyme cleaves IgA1 in the hinge region, separating
Fab and Fc; this inactivates IgA function. IgA protease also
cleaves other proteins such as endosomal Lamp1, important
for intracellular vesicle trafficking. The functions of other
secreted proteins including the filamentous hemagglutinin
(FHA)-like protein TpsA and FrpA/C are largely unknown.
Asubset(80 %) of meningococcal and gonococcal strains
Meningitis 18 409
secrete DNA via a type IV secretion system
(Hamilton et al. 2005). The genes encoding this system are
located on the gonococcal genetic island, a DNA region that
is acquired by horizontal gene transfer. Unlike many other
bacterial pathogens, Neisseria spp. lack a type III secretion
Meningococcal Genome Characteristics
and Dynamics
Neisserial chromosomes are 2.2–2.3 Mb in length with an
average G+C content of 48–56 mol%. Approximately 95 %
of the genic material, excluding intergenic regions, is
shared between N.meningitidis and N.gonorrhoeae (Claus
et al. 2007). The vast majority of genes are also present in
nonpathogenic N.lactamica, but the same gene may be
differentially regulated in pathogenic and commensal strains.
The meningococcal and gonococcal genomes are considered to
be hyperdynamic (Davidsen and Tonjum 2006), and the high
level of genomic plasticity/instability is thought to contribute to
pathogenicity and development of hypervirulence. The most
important sources of neisserial genome instability are:
1. Phase variation, reflecting slip mispairing in homopolymer
nucleotide runs at or near the promoter or in open reading
frames (affect translation)
2. Recombination, integration, or rearrangement of DNA from
external or internal sources
3. Horizontal gene transfer via uptake of exogenous or
‘‘foreign’’ DNA, with subsequent RecA-mediated integration
into homologous region of the genome
4. Hypermutation due to error-prone DNA repair, replication
infidelity, or overexpression of error-prone translesion DNA
Meningococci are naturally competent for DNA uptake
throughout their growth cycle (Jyssum and Lie 1965; Sparling
1966; Hamilton and Dillard 2006; Ambur et al. 2009).
The pathogenic Neisseria spp. share several genomic regions
including up to nine prophage and eight genetic islands that
are absent from N.lactamica (Snyder et al. 2005). In contrast to
many other bacterial species, there are no classical pathogenicity
islands in N.meningitidis.N.meningitidis-specific DNA
sequences include the cps locus encoding the polysaccharide
capsule, genes that encode the RTX family of toxins, and an
ortholog of the filamentous hemagglutinin of Bordetella
pertussis. The genomes of disease and carriage isolates show no
consistent differences. Certain hypervirulent lineages contain
the filamentous prophage Nf1 (Bille et al. 2005). N.meningitidis
strains of serogroups W-135, H, and Z contain the ‘‘gonococcal
genetic island’’ (GGI, 57 kb) (Snyderand Saunders 2006). This is
an often chromosomally integrated conjugative plasmid that
encodes a type IV secretion system involved in DNA secretion.
The genome of Neisseria spp. has a variable number of
noncoding repeat arrays and insertion (IS) elements among
which IS1655 appears to be unique to N.meningitidis.
Most isolates of N.gonorrhoeae, but not of N.meningitidis,
carry plasmids (Roberts 1989). Nearly all gonococcal strains
carry a 4.2-kb cryptic plasmid of unknown function, and many
strains carry plasmids encoding b-lactamase, which confers
resistance to penicillin. The conjugative plasmid TetM
confers tetracycline resistance.
Genome-based phylogenetic reconstruction indicates that
pathogenic N.meningitidis emerged from a common
unencapsulated ancestor by acquisition of capsule genes has
several hundred years ago, probably from members of the family
Pasteurellaceae (Schoen et al. 2008).
Pathogenesis of Meningococcal Meningitis
Humans are the only host for the meningococcus and the
pneumococcus. N.meningitidis frequently colonizes the
human pharynx as well as buccal mucosa, rectum, urethra,
urogenital tract, and dental plaque. The most common natural
habitat of the meningococcus is the epithelial cells of the naso-
and posterior pharynx and the tonsils. N.meningitidis is carried
in the pharynx by 4–25 % of the human population. Thus, there
are hundreds of millions of carriers worldwide, and adolescents
are a principal reservoir (Rosenstein et al. 2001).
Invasive strains of meningococci express capsules, and
pathological meningococcal strains were originally distinguished
from nonpathological strains by differences in capsular polysac-
charide structure (Kim 2003). Virulence determinants include
the polysaccharide capsule, outer membrane proteins
including pili, the porins (PorA and PorB), the adhesion
molecule, Opc, iron sequestration mechanisms, and endotoxin
(lipooligosaccharide) (de Louvois et al. 2005).
N.meningitidis is classified into 13 serogroups based on the
immunogenicity and structure of the polysaccharide capsule.
Further classification into serosubtype, serotype, and
immunotype is based on class 1 outer membrane proteins
(PorA), class 2 or 3 (PorB) outer membrane proteins, and
lipopoly[oligo]saccharide structure, respectively (Chang et al.
2004; Jolley et al. 2012). PorA is an important target for
bactericidal antibodies. In addition to these specific virulence
factors, N.meningitidis has evolved and exploits genetic
mechanisms that result in high-frequency phase and antigenic
variation and molecular mimicry. Capsule switching, due to
allelic exchange of capsule biosynthesis genes by transformation,
is one mechanism by which meningococci evade immune
detection (Fothergill and Wright 1933).
Infection by N.meningitidis commonly develops in asymp-
tomatic individuals carrying bacteria in the oronasopharyngeal
cavity (Yazdankhah and Caugant 2004). Type IV pili facilitate
initial adherence and opacity-associated proteins (Opa and
Opc) and PorB trigger uptake of the bacteria into the cells,
largely by similar types of receptors (CEACAM, HSPG). Opa
variants are found in hyperinvasive meningococcal lineages. Opa
and Opc bind to heparin and interact with vitronectin and
410 18 Meningitis
fibronectin, promoting transport into cells via integrin receptors
(Duensing et al. 1999). This is accompanied by
a downregulation of pili and capsule enabling optimal contact
between bacterial adhesins and the host mucosa. Transferrin
(TbpA, TbpB) and hemoglobin (Hbp) bind and sequester iron
to support bacterial growth (Perkins-Balding et al. 2004).
Ciliated mucosal cells can be damaged by released peptidogly-
can fragments and LOS. However, the oropharyngeal
region has a relatively tolerance for foreign matter and is rela-
tively refractory to the typical inflammatory response charac-
teristic of more sterile anatomical niches such as the urethra.
This may explain why meningococcal (and gonococcal)
colonization of the oropharynx is rarely associated with
clinical disease.
The few phylogenetic groups of N.meningitidis that cause
meningococcal disease often carry a filamentous prophage in
their genome that is secreted from the bacteria via the type IV
pilin secretin (Bille et al. 2005). The prophage may promote the
development of new epidemic clones. The mechanism by which
meningococci penetrate and pass through the mucosa is only
partially understood (Merz and So 2000). Meningococci survive
and multiply during epithelial cell traversal. The IgA1 protease
and PorB may promote survival inside epithelial cells. Menin-
gococci isolated from the bloodstream invariably produce poly-
saccharide capsule. The capsule protects the bacterium from
phagocytosis and complement-mediated lysis by preventing
insertion of the terminal complement attack complex. Invasive
meningococci express sialylated LOS which influences binding
of C4b, while the proteins PorA and GNA1870 recruit the
negative regulators of complement activation C4BP and
factor H (Schneider et al. 2007). Individuals with inherited
deficiencies in the late complement components (C5–C9) have
a high risk in developing meningococcal disease. Intriguingly,
they acquire the infection at a much later age and have frequent
recurrences, and the case fatality rate is much lower than for
normocomplementemic individuals.
In the blood, N.meningitidis replicates to high levels (up to
/mL plasma) and sheds outer membrane vesicles (blebs)
(Stephens and Greenwood 2007). The blebs may subvert the
complement system, and high levels of circulating LOS
overactivate the innate immune system. Circulating levels of
proinflammatory mediators (TNF-a, IL-1, and IL-6) strongly
correlate with development of lethal septic shock (Stephens et al.
2007; Brandtzaeg and van Deuren 2012).
Meningococci and pneumococci most often enter the CSF
likely by the hematogenous route via the capillaries and veins in
the subarachnoid space (the blood–CSF barrier) and the choroid
plexi rather than through the brain parenchyma (blood–brain
barrier). Encapsulated N.meningitidis invade the CSF probably
via the transcellular route (Nikulin et al. 2006). The absence of
non-opsonophagocytosis in CSF initially enables uncontrolled
bacterial growth and inflammation of the leptomeninges and
subarachnoid space. In the CSF, N.meningitidis produce poly-
saccharide capsule and pili and stimulate proinflammatory cyto-
kine (Il-6, IL-8, MCP-1) and chemokine (RANTES, GM-CSF)
production in meningeal cells (Christodoulides et al. 2002).
Attracted polymorphonuclear cells aggravate the inflammatory
response and release cytotoxic mediators.
Immunity to invasive meningococcal disease depends upon
the presence of bactericidal IgG antibodies directed against
capsule (except serogroup B), PorA, PorB, Opa, LOS,
iron-regulated proteins, and minor surface proteins. Carriage
of nonpathogenic Neisseria spp. (e.g., N.lactamica) in the
nasopharynx elicits cross-reactive antibodies that contribute to
development of immunity against N.meningitidis. In vivo phase
and antigen variation of meningococcal surface antigens indi-
cate selective immunological pressure during natural infection.
Pathogenesis of Pneumococcal Meningitis
The mechanisms underlying pneumococcal meningitis are not
fully understood, but involve bacterial, host, as well as environ-
mental factors. The route from the initial site of infection to the
meninges is believed to occur via a bacteremic phase and
subsequent traversal of the organism from the circulation across
the blood–brain barrier (BBB) into the subarachnoid space.
However, animal experiments suggest direct axonal retrograde
transport to the brain without detectable bacteremia, in
a process requiring pneumococcal interactions with gangliosides
(van Ginkel et al. 2003). There is some epidemiological support
for this, in that pneumococcal CSF isolates belong to a multitude
of serotypes more reflective of the commensal nasopharyngeal
flora than to blood isolates (Henriques Normark et al. 2001).
It is believed that pneumococci exploit selective tropism
towards brain endothelial cells to invade into the CSF. The
main pathogens causing bacterial meningitis, S.pneumoniae,
N.meningitidis, and H.influenzae all interact with the laminin
receptor on rodent as well as HBMECs. In pneumococci, this
interaction is mediated by choline-binding protein CbpA
(PspC) on the pneumococcal surface. The binding site on
CbpA for the laminin receptor was localized to a highly
conserved, surface-exposed loop not involved in other known
CbpA–host interactions (Orihuela et al. 2009).
All pneumococcal isolates possess the nanA gene encoding
a cell-wall-anchored neuraminidase that cleaves sialic acid from
host cells and proteins. The lectin moiety of NanA rather than
the sialidase region promotes pneumococcal adherence to and
entry into HBMECs, suggesting that bacterial binding to
sialylated glycoconjugates might represent an early step in the
BBB translocation process (Uchiyama et al. 2009). In addition,
lectin-bound NanA activates brain endothelial chemokine
expression and recruits neutrophils, promoting a local inflam-
matory response at the site of infection even the absence of
invasion (Banerjee et al. 2010). This proinflammatory response
of pneumococcal NanA requires unmasking of an inhibitory
sialic acid-binding receptor on the surface of immune cells
(Chang et al. 2012). Other data also suggest that local
proinflammatory events that trigger endocytosis and/or locally
damage HBMECs facilitate transport across the BBB.
Cell surface phosphorylcholine on pneumococci can bind
the human platelet-activating factor receptor, activating
Meningitis 18 411
beta-arrestin-mediated uptake of pneumococci into cells within
the BBB (Radin et al. 2005). Pneumococcal-induced death of
brain endothelial cells can be mediated by cell-wall components
via TLR2 signaling and/or via the pore-forming cytotoxin
pneumolysin and the unusually high levels of hydrogen peroxide
produced by this catalase-negative organism (Bermpohl et al.
2005). TLR stimulation mediated by pneumococci is sufficient
to promote translocation of the organism as well as its inflam-
matory components across the epithelium by downregulation of
genes involved in the formation of tight junctions (Clarke et al.
2011). It is, however, not known whether innate immune
activation by pneumococci opens tight junctions in the brain
endothelium, even though early work demonstrated that
intracisternal infection in rats by S.pneumoniae serotype 3 caused
morphological changes in cerebral endothelium including
completely separated cell junctions (Quagliarello et al. 1986).
Once pneumococci have entered the CSF, they proliferate
easily and release large quantities of proinflammatory compo-
nents that are recognized by resident immune cells via cell
surface and intracellular pattern recognition receptors such as
TLRs. This leads to high production of cytokines and
chemokines that accumulate in CSF, contributing to inflamma-
tion-mediated brain damage. Several cytokines increase in CSF
from meningitis patients including IL-1beta. In CSF, IL-1beta
concentration correlates with CSF leukocyte count and clinical
outcome (Mustafa et al. 1989). IL-1beta activation results from
induction of the precursor pro-IL-1beta typically mediated by
TLR signaling and inflammasome-controlled activation of
caspase 1 cleaving the pro-IL-1beta into active IL-1beta. It has
been demonstrated that the ASC and NLRP3 components of the
inflammasome promote inflammatory damage in a murine
pneumococcal meningitis model and that pneumococcal
pneumolysin is the main inducer of IL-1beta expression and
inflammasome activation upon pneumococcal challenge
(Hoegen et al. 2011). However, infection of human dendritic
cells revealed that pneumolysin inhibits human dendritic cell
maturation, induction of proinflammatory cytokines, and acti-
vation of the inflammasome testifying to important differences
between human and murine immune cells in their responses to
pneumolysin (Littmann et al. 2009).
Pneumolysin and other cytolysins can also have a direct toxic
effect on cortical neurons independent on leukocyte infiltration
and caspase activation as demonstrated in an infant rat
meningitis model. The damaging effect on cortical neurons
due to pore-forming cytolysins was shown to be age dependent
and more pronounced in 7- as compared to 11-day-old rats
(Reiss et al. 2011). The cytolytic effects of pneumolysin on
brain tissue astroglia were significantly enhanced by reducing
the calcium concentration (Wippel et al. 2011).
The large quantities of H
produced by the catalase-
negative pneumococci besides causing oxidative damage have
also been shown to affect brain tissue in other ways. Thus, H
produced by pneumococci contributed to regional hyperemia in
an experimental meningitis model (Hoffmann et al. 2007).
Pneumococcal production of H
was also responsible for
the observed transcriptional activation of brain thrombopoietin
and its receptor (c-Mpl) after intrathecal infection.
Thrombopoietin is known to exhibit proapoptotic effects on
neurons, and its upregulation upon pneumococcal infection
may therefore have neurotoxic effects (Hoffmann et al. 2011).
The high expression of H
is normally attributed to the
pneumococcal spxB gene encoding a pyruvate oxidase. In vivo
transcriptomic analyses of mouse brain tissue, after induction of
pneumococcal meningitis, revealed an upregulation of the glpO
gene encoding an alpha-glycerophosphate oxidase that was cyto-
toxic for HBMECs via generation of H
.AglpO deletion
mutant was defective in the progression from the blood to the
brain during in vivo infection, and mutant bacteria caused
a significantly lower meningeal inflammation and brain pathol-
ogy compared with wild type. Interestingly, GlpO immunization
protected against pneumococcal invasive disease (Mahdi et al.
Even though brain lesions appear to result from local men-
ingeal infection, experimental infection demonstrates that the
systemic bacteremic component in pneumococcal meningitis
significantly contributes to clinical disease presentation and the
pathophysiology of BBB breakdown and ventricle expansion
(Brandt et al. 2008).
By comparing host response proteins in the CSF from
survivors with non-survivors with pneumococcal invasive
disease, it was found that complement C3 levels were fivefold
lower in non-survivors, suggesting that C3 depletion in CSF is a
major factor contributing to death in pneumococcal meningitis.
Also, transferrin levels in CSF were higher in the group of
non- survivors suggesting a more extensive damage of the
blood–brain barrier. There were however no differences in the
level of cortical necrosis in the two patient groups as monitored
by the CSF levels of creatinine kinase BB (Goonetilleke et al.
2012). The central role played by the complement system in
protecting the CNS against pneumococcal growth has also
been demonstrated in a murine meningitis model. Thus, 24 h
after intracisternal infection, bacterial titers in the CNS were
almost 12- and 20-fold higher in C1q- and C3-deficient mice,
respectively, than in wild-type mice (Rupprecht et al. 2007).
The cell-wall component lipoteichoic acid has been
suggested to be a pattern recognition molecule and inflamma-
tory mediator; however, the receptor for this interaction
remains controversial. Interestingly, intrathecal treatment with
antibodies against phosphorylcholine recognizing teichoic and
lipoteichoic acids decreases neuronal damage in experimental
pneumococcal meningitis.
Clinical Features
Severity of illness on presentation, infection with antimicrobial-
resistant organisms, and incomplete knowledge of the
pathogenesis of meningitis are factors that contribute signifi-
cantly to mortality and morbidity associated with bacterial
meningitis (Chang et al. 2004; Davidsen et al. 2007). When
bacterial meningitis is suspected, immediate action is imperative
to establish a definitive diagnosis, and antimicrobial treatment
412 18 Meningitis
must be initiated as soon as possible as a precautionary measure,
because the mortality rate for untreated bacterial meningitis
approaches 100 %; even with optimal treatment, mortality and
morbidity remain high.
However, especially in children, the symptoms and signs
depend on the age of the child, the duration of illness, and the
host response to infection (Tonjum et al. 1983). Notably, the
clinical features of bacterial meningitis in infants and children
can be subtle, variable, nonspecific, or even absent. In infants,
they might include fever, hypothermia, lethargy, irritability, poor
feeding, vomiting, diarrhea, respiratory distress, seizures, or
bulging fontanelles. However, at a certain stage, even infants
develop nuchal rigidity. In older children, clinical features include
fever, headaches, photophobia, nausea, vomiting, confusion,
lethargy, or irritability. Other signs of bacterial meningitis on
physical examination include neck and back rigidity, Kernig’s
sign (flexing the hip and extending the knee to elicit pain in the
back and legs), Brudzinski’s sign (passive flexion of the neck elicits
flexion of the hips), focal neurological findings, and increased
intracranial pressure. Signs of meningeal irritation are present in
75 % of children with bacterial meningitis at the time of
presentation (Levy et al. 1990; Borchsenius et al. 1991). Absence
of meningeal irritation in children with bacterial meningitis is
substantially more common in those younger than 12 months.
The constellation of systemic hypertension, bradycardia,
and respiratory depression (Cushing’s triad) is a late sign of
increased intracranial pressure. Neurological sequelae are
relatively common in survivors of meningitis, especially in
individuals infected by a pneumococcal microorganism
(Arditi et al. 1998; Roine et al. 2008).
Meningococcal Meningitis. The clinical spectrum of systemic
meningococcal disease includes meningitis/meningoencephalitis,
fulminant septic shock, the combination of the two, or mild
meningococcemia without clinically distinct meningitis. Occasion-
ally, the bacteremia leads to localized joint infection, pericarditis,
panophthalmitis, and subchronic or chronic meningococcemia
(Rosenstein et al. 2001; Stephens et al. 2007; Brandtzaeg and
van Deuren 2012).
The most frequent form of meningococcal infection is acute
pyogenic meningitis due to inflammation of the meninges.
Based on distinct clinical symptoms of 862 patients in three
prospective studies with documented meningococcal disease,
37–49 % had meningitis without shock, 13–20 % meningitis
with shock, 10–18 % shock without meningitis, and 18–33 %
mild meningococcemia without meningitis or shock
(Brandtzaeg and van Deuren 2012). Using the same classifica-
tion of meningococcal patients admitted to a tertiary academic
hospital, the blood culture was positive in 50 % of patients with
meningitis without shock, 87 % of patients with meningitis
and shock, 93 % of patients with shock without clinically dis-
tinct meningitis, and 77 % of patients without meningitis or
shock. Interestingly, the CSF culture was positive in 84 % with
meningitis without shock, 83 % in those with meningitis and
shock, 59 % in shock without clinically distinct meningitis, and
in 47 % in those without clinically distinct meningitis or shock
(Brandtzaeg 2006).
N.meningitidis has the propensity to invade the meninges
and will do so in most cases left untreated. Even in the most
fulminant cases of septic shock reaching the hospital in Europe
within median 12 h, 59 % had a positive CSF culture. Invasive
meningococcal infections lead to compartmentalized bacterial
proliferation. In patients with clinically distinct meningitis, the
levels of meningococci and inflammatory mediators are several
logs higher in the CSF than the blood. Conversely, in patients
presenting with septic shock, the bacterial proliferation and the
inflammatory response mainly occur in the circulation with
bacterial load and inflammatory response several logs higher
than the subarachnoid space. Thus, the clinical presentation
depends on the velocity of proliferation in the blood. Low-graded
proliferation leads gradually to meningitis within median 24 h
(van Deuren 2001; Brandtzaeg 2006; Stephens 2007; Brandtzaeg
2012). Bacterial load and level of LOS in the circulation
are below the shock (10 endotoxin units/mL) threshold.
In those developing septic shock, the proliferation is very
rapid, the bacterial load massive with up to 10
/mL, and
LOS activity as high as 2150 endotoxin unites/mL (van Deuren
2001; Brandtzaeg 2006; Stephens and Greenwood 2007;
Brandtzaeg 2012).
For unknown reasons, patients in the large meningococcal
epidemics in sub-Saharan Africa usually develop meningitis
without shock and severe DIC, leading to large hemorrhagic
skin lesions and thrombosis and subsequent gangrene of
peripheral extremities.
On admission, 60 % of cases have experienced symptoms for
less than 24 h and 12–20 % for less than 2 days (Tønjum et al.
1986). These symptoms can occur discretely or can blend into
one another during clinical disease progression. The disease
usually begins abruptly with headache, meningeal signs includ-
ing stiffness of the neck, and fever. However, classic signs of
meningitis (i.e., confusion, headache, fever, and nuchal rigidity)
are seen in only about one-half of infected patients. Very young
children often have only nonspecific signs including fever,
abdominal pain, and vomiting. Other signs include reduced
consciousness and photophobia. Mortality approaches 100 %
in untreated cases but is around 10 % when appropriate antibi-
otic therapy is instituted. The incidence of neurological sequelae
is low, with hearing deficits, epilepsy, and arthritis most com-
monly noted. These sequelae are most probably underreported.
In CSF, the number of bacteria is higher than in plasma,
leading to a large compartmentalized inflammatory response in
the subarachnoid space, with pronounced increase in the
concentration of endotoxin, tumor necrosis factor-a(TNF-a),
interleukins (IL-1b, IL-6, IL-8, and IL-10), chemokines, and
other mediators. The overall inflammatory response in the
systemic vasculature, as indicated by activation of cytokines
and complement, is modest (Turner et al. 1990; Latorre et al.
2000; Chang et al. 2004; Dubos et al. 2008). Meningococcemia
can manifest as pink maculopapular petechial eruptions
(Stephens et al. 2007). Rapidly progressive infections can be
accompanied by in purpuric/petechial or ecchymotic skin
lesions that are hemorrhagic and necrotic. However, skin lesions
can be atypical, evanescent, or even entirely absent in patients
Meningitis 18 413
who have blood culture-positive meningococcal sepsis. Fulmi-
nant shock can dominate the clinical picture in patients with
acute meningococcal sepsis (Stephens et al. 2007; Brandtzaeg
and van Deuren 2012). Sepsis can progress to disseminated
intravascular coagulation (DIC) characterized by increasing
petechiae or purpura fulminans, resulting in extensive areas of
tissue destruction secondary to coagulopathy, rapid onset of
hypotension, and adrenal hemorrhage (Waterhouse–
Friderichsen syndrome). Gangrenous cases in the extremities
can occur due to thrombosis, and death is usually caused by
cardiovascular collapse (>Fig. 18.3).
The clinical diagnosis of meningococcal meningitis begins with
recognition of fever, petechial rash, meningeal signs, and altered
mental status and is confirmed by pleocytosis, Gram stain with or
without culture of CSF, or blood or skin lesions. The early diag-
nosis of meningococcemia is difficult when rash and meningeal
signs are not present. General symptoms of sepsis (leg pains, cold
hands and feet, abnormal skin color) develop first in patients with
severe meningococcemia (Borchsenius et al. 1991; Tonjum et al.
1983). However, these symptoms are not specific to meningo-
coccal and pneumococcal disease. Parents and relatives should
be instructed to undress and inspect a febrile child, adolescent,
or young adult for rash, and physicians and health-care
providers should heed the concern of parents or relatives, if and
when they describe abrupt or rapid deterioration of a patient.
Laboratory Diagnosis of Meningitis
It is of paramount importance to examine the CSF in order to
properly diagnose all forms of meningitis. Cerebrospinal fluid
(CSF), blood, skin biopsies, nasopharyngeal swabs, and aspirates
are relevant specimens for the diagnosis of meningococcal and
pneumococcal disease. Synovial fluid, sputum, and conjunctival
swabs can also be cultured, if clinically indicated. Because
meningococci and pneumococci are susceptible to desiccation
and temperature extremes, specimens should be cultured as
soon as possible after collection.
For presumptive diagnosis, specimens are examined by Gram
and acridine orange stain. Gram- and acridine orange-stained
smears are made directly from CSF, if the CSF is cloudy or after
centrifugation when the CSF is clear. The majority of the smears
will show Gram-negative diplococci inside and outside polymor-
phonuclear cells when the CSF bacterial count is >10
Approximately 25 % of smears will stain positively with Gram
stain when the bacterial density in the CSF is <10
mL; on
average, 60–90 % of CSF specimens that are culture positive
are stain positive. Gram-stained smears combined with culture
from disease-related petechial skin lesions detect meningococci
in 62 % of cases (Stephens and Greenwood 2007).
Meningococcal capsular polysaccharides are detected directly
in CSF by performing latex agglutination and coagglutination
with polyclonal antibodies for serogroups A, B, C, Y, and W-135
(Chanteau et al. 2007). These methods can detect 0.02–0.05 mg of
antigen per mL, with a sensitivity of approximately 50 %, com-
pared to 82–90 % for direct detection of meningococci in CSF and
.Fig. 18.3
(a) A young woman with sepsis and hemorrhagic skin lesions in the face caused by S.pneumoniae. She also had ecchymosis on the
extremities. (b) Hemorrhagic skin lesions in a man with fulminant S.pneumoniae sepsis. (c) Hemorrhagic skin lesions in the face
of a man with fulminant S.pneumoniae sepsis. He also had similar lesions on the body and extremities (Petter Brandtzæg)
414 18 Meningitis
blood by NAATs/PCR (Taha and Fox 2007). The latter tests are
also useful for confirming the diagnosis in patients treated with
antibiotic prior to sample collection or who tests negative in all
prior testing (i.e., Gram stain, antigen test, and culture).
Positive Gram stain is observed in approximately 90 % of
children with pneumococcal meningitis, 80 % of children with
meningococcal meningitis, half of patients with Gram-negative
bacillary meningitis, and a third of patients with Listeria
meningitis (La Scolea and Dryja 1984). When CSF is first
clarified by Cytospin centrifugation, the fraction of samples
that stain positively increases (Shanholtzer et al. 1982). CSF
cell count and differential, and concentrations of protein and
glucose often help with differential diagnosis of various forms of
meningitis. The proportion of polymorphonuclear cells in CSF
from patients who have meningitis ranges from 49 % to 98 %
(mean of 86 %). The prognosis is poor when patients present
with low white blood cell count and positive Gram staining
in CSF. CSF culture can be negative in children who receive
antibiotic treatment before CSF examination. During a course
of antibiotic treatment, the CSF leukocyte count, glucose and
protein concentration, and antigen tests are abnormal for several
days, even though bacteria might not be evident on smear or by
CSF culture. Blood cultures test positive in only 50 % of
the patients with meningococcal and pneumococcal disease.
In those who have received antibiotics prior to the collection
of blood for culture, blood cultures are sterile. A nasopharyngeal
swab from young children will provide valuable information in
cases of suspected meningococcal and pneumococcal disease.
For isolation of N.meningitidis, the clinical specimen should
be inoculated on selective and nonselective growth media
(Tonjum 2005). Appropriate nonselective media are 5 % sheep
or human blood agar and chocolate agar. Meningococci and
pneumococci are grown on agar media in a 5–10 % carbon
dioxide-enriched atmosphere with rather high humidity at
35–37 C (95–98.6 F). After 18–24 h, flat, gray–brown,
translucent, smooth, 1–3 mm colonies of N.meningitidis or
S.pneumoniae are present which can be analyzed by Gram
stain (Tonjum 2005). The finding of oxidase- and catalase-
positive Gram-negative diplococci is sufficient to support
a tentative diagnosis of meningococcal disease. Differentiation
characteristics are the production of acid from glucose
and maltose. Optochin-sensitive bacteria with a characteristic
central umbilicus indicate S.pneumoniae. Isolation of
N.meningitidis and S.pneumoniae can also be finally confirmed
by nucleic acid amplification technique (NAATs/PCR), DNA
sequence, or MALDI/TOF analysis.
Non-culture Methods. Non-culture tests are particularly
important for patients who need rapid identification of
pathogens or have previously received antibiotics, or whose
initial CSF Gram stain is negative with negative culture at 72-h
incubation. Such tests include latex agglutination, PCR,
loop-mediated isothermal amplification method, microarray
or biochip, and immunochromatography. Latex agglutination
uses latex beads adsorbed with microbe-specific antibodies.
In the presence of homologous antigen, there is visible aggluti-
nation of the antibody-coated latex beads (Gray and Fedorko
1992). In a multicenter pneumococcal meningitis surveillance
study, latex agglutination was positive in 49 (66 %) of 74 CSF
samples that grew S.pneumoniae and in four of 14 CSF samples
that were culture negative. The use of standard or sequential-
multiplex PCR has been shown to be useful in identification of
infecting pathogens in patients who have previously received
antibiotics or in resource-poor settings (Corless et al. 2001;
Schuurman et al. 2004; Saha et al. 2008; Chiba et al. 2009).
Multiplex real-time PCR or broad-range PCR aimed at the 16S
ribosomal RNA gene of eubacteria is promising for the detection
of pathogens from CSF. The detection rate was substantially
higher with PCR than with cultures in patients who had previ-
ously received antibiotics (Chiba et al. 2009). However, the limit
of detection differs between assays. Real-time PCR has been
shown to detect as few as two copies of N.meningitidis,S.
pneumoniae,and E.coli, 16 copies of L.monocytogenes, and 28
copies of group B streptococcus, whereas the sensitivity for
broad-range 16S ribosomal DNA PCR was about 10–200 organ-
isms per mL CSF (Lu et al. 2000; Schuurman et al. 2004). The
time needed for the whole process from DNA extraction to the
end of real-time PCR was 1.5 h (Chiba et al. 2009), an attractive
timeframe for its application in clinical practice. A Gram-stain-
specific probe-based real-time PCR using 16S ribosomal RNA
has been shown to allow simultaneous detection and discrimi-
nation of clinically relevant Gram-positive and Gram-negative
bacteria directly from blood samples (Wu et al. 2008), which
might provide more rapid and accurate diagnosis of bacterial
meningitis. In addition, sequential PCR-based serotyping of S.
pneumoniae using serotype-specific primers could improve
ascertainment of pneumococcal serotype distribution in settings
in which prior use of antibiotics is high (Saha et al. 2008).
A recently developed NAAT, loop-mediated isothermal amplifi-
cation, which amplifies DNA under isothermal conditions
(63 C), is a promising tool, particularly in resource-poor set-
tings, because it does not require a thermocycling apparatus and
the results can be read with the naked eye (based on turbidity or
color development by SYBR Green dye for staining nucleic
acids) (Seki et al. 2005). The assay detected ten or more copies
of S.pneumoniae in oral mucosa swab samples (Seki et al. 2005),
but its use in the diagnosis of bacterial meningitis has not been
tested. Identification of pathogens by use of a microarray or
biochip involves extraction of genomic DNA from CSF, ampli-
fication of targeted DNA, and hybridization of labeled DNAwith
oligonucleotide probes (pathogen-specific or virulence genes)
immobilized on a microarray. A rapid immunochroma-
tographic test for S.pneumoniae was evaluated in 122 children
with pneumococcal meningitis (Saha et al. 2005). Compared
with CSF culture (sensitivity of 71 %) and latex agglutination
(86 %), immunochromatography was 100 % sensitive for the
diagnosis of pneumococcal meningitis, suggesting that
immunochromatography might be useful in the diagnosis of
pneumococcal meningitis.
PCR or other non-culture tests can be especially useful for
diagnosis in regions where patients frequently receive antibiotics
before reaching the hospital. Recent WHO reports may have
underestimated the real disease burden, because bacteremia and
Meningitis 18 415
severe (fatal) disease are often not reported. Further underesti-
mation may be due to limited resources for establishing
a diagnosis. In many, but not all, developing countries, at least
one laboratory is available for the surveillance of meningococcal
disease, but limitations in the availability of diagnostic and
typing methods may further result in underestimation of disease
Molecular Typing of N.meningitidis
Phenotypic classification of N.meningitidis is based upon
antigenic differences of the major surface antigens which
provides information about the serogroup (capsule, e.g., B),
serotype (PorB porin, e.g., 15), serosubtype (PorA porin, e.g.,
P1.7), and LOS immunotype (e.g., L3) of a particular strain.
This results in the classification: B, 15, P1.7, and L3. Multiple
epitopes can be recognized depending upon the presence
of phase or antigen variants in the bacterial population.
Antigen-based typing is currently only relevant for vaccine
efficacy studies.
A genetic typing system based upon polymorphisms in mul-
tiple housekeeping genes (multilocus sequence typing or MLST)
is the gold standard for molecular typing and has defined
hypervirulent meningococcal lineages (Maiden et al. 1998).
Why hypervirulent meningococcal lineages are more pathogenic
has been a subject of considerable interest. Based on sequencing
of eight genomes, the chromosome is between 2.0 and 2.1 Mb in
size and contains about 2,000 genes (Parkhill et al. 2000; Tettelin
et al. 2000; Schoen et al. 2008). Each new strain sequenced has
identified 40–50 new genes, and the meningococcus shares
about 90 % homology at the nucleotide level with either
N.gonorrhoeae or N.lactamica. Mobile genetic elements includ-
ing IS elements and prophage sequences make up 10 % of the
genome (Parkhill et al. 2000). Other than the capsule locus, no
core pathogenome has been identified, suggesting that virulence
can be clonal group dependent. Given that transformation is an
efficient mechanism of genetic exchange and that meningococci
have acquired DNA from commensal Neisseria spp. and other
bacteria (e.g., Haemophilus) as well as phages, the gene pool for
adaptation and evolution is quite large. Genome plasticity and
phenotype diversity through gain and loss of DNA or, for exam-
ple, through DNA repeats are characteristics of meningococcal
evolution. This is in contrast to the relatively conserved genomes
of, for example, Bacillus anthracis. The acquisition of the capsule
locus by horizontal transfer possibly from Pasteurella multocida
or P.haemolytica (Schoen et al. 2008) appears to be a major event
in the evolution of the pathogenicity of the meningococcus.
Many molecular methods are being used to characterize
the structure and evolution of the N.meningitidis genome.
These include multilocus enzyme electrophoresis (ET) typing,
DNA restriction analysis, randomly amplified polymorphic DNA
(RAPD), restriction fragment length polymorphism (RFLP),
and ribotyping (Yazdankhah and Caugant 2004). The current
strain typing method, MLST, shows that epidemics are often
caused by specific complexes of related hypervirulent lineages
(Maiden et al. 1998; Yazdankhah and Caugant 2004). MLST is
presently the best method for global typing of meningococci and
for understanding the impact of vaccination. As has been the
case for the W-135 epidemic in Africa, surveillance can direct the
preparation of vaccines against new clonal strains or specific
serogroups (Khatami and Pollard 2011). However, the
robustness of MLST in predicting antigenic profile needs further
analysis. Especially in the context of new protein-based menin-
gococcal vaccines, the expansion of current typing protocols
needs consideration. Because MLST uses conserved core
sequences, it may not necessarily predict associations between
many vaccine antigens because of the lack of concordance
introduced by recombination. Targeted and complete
genome sequencing is now the method of choice for genotyping
(Jolley et al. 2012).
Molecular Typing of S.pneumoniae
S.pneumoniae is highly diverse genetically, due to an efficient
transformation system. Some of the many clonal lineages in the
genus cause severe pneumonia with invasive disease or
meningitis. On the other hand, other lineages are colonizers
that are less virulent and being less lethal, and they instead
tend to promote the spread of antibiotic resistance. Comparative
genomic analyses and functional studies reveal that a significant
fraction of the pneumococcal genome is variable and not
conserved in all strains. These genomic regions encode
nonessential ‘‘accessory’’ gene products, which, at least in
mouse models, alter virulence (Blomberg et al. 2009).
A number of pneumococcal genomes have been sequenced
completely, revealing that the core pneumococcal genome, the
portion that is conserved between strains, comprises approxi-
mately 50 % of all pneumococcal genes (Hiller et al. 2007).
Hence, the accessory genome is of considerable size and may
provide different pneumococcal strains (clones) with different
properties. Molecular tools such as pulse field gel electrophoresis
(PFGE) and multilocus sequence typing (MLST) (partial
sequencing of seven housekeeping genes) have allowed direct
strain comparisons from the same or different geographic areas
(Blomberg et al. 2009). Together, these studies show that the
capsule and its accessory components are the major virulence
attribute of the pneumococcus. Based on difference in capsular
components, at least 93 capsular serotypes have been identified.
Epidemiological studies that compared carrier and invasive iso-
lates from the same geographic area over the same time period
revealed that different serotypes have different odds ratios (ORs)
of causing invasive disease (Brueggemann et al. 2003; Sandgren
et al. 2004). However, strains of different MLST (ST) but with
the same serotype display different degrees of virulence in mice
(Sandgren et al. 2005). Thus, the OR for risk of invasive disease
varies between strains of the same serotype and between strains
of the same ST type as well as by some host characteristics
including age and health status, as discussed above (Sjostrom
et al. 2006). Therefore, disease severity and disease outcome are
affected by the capsular type as well as by other pneumococcal
416 18 Meningitis
properties, especially those encoded by the variable accessory
genome, and by characteristics of the host.
The serotype and clonal distribution for pneumococcal
meningitis is broader than for cases of septicemia caused by
the same organism (Henriques et al. 2000; Henriques Normark
et al. 2001; Darenberg and Henriques Normark 2009). Clinical
presentation and outcome of pneumococcal meningitis also
vary for pneumococcal strains of different genotypes (van
Hoek et al. 2012). For example, Burckhardt et al. found in
a prospective population-based study that serotype 23F was an
independent risk factor for pneumococcal meningitis
(Burckhardt et al. 2010). In France et al. showed that despite
a high vaccination rate, the incidence of pneumococcal menin-
gitis did not decline between 2001–2002 and 2007–2008, due to
a wide diversity of serotypes causing pneumococcal meningitis
after vaccine introduction (see below) (Levy et al. 2011). How-
ever, they observed a decline in cases in children younger than
2 years of age, which was offset by an increase in older children.
Host Susceptibility to Meningococcal
and Pneumococcal Meningitis
Genetic Cofactors. Absence of protective bactericidal antibodies
is the most important single predisposing factor for systemic
meningococcal and pneumococcal disease, but genetic polymor-
phisms and other host cofactors contribute to disease (Sanders
et al. 2011). Complement deficiency and polymorphisms in
other innate host determinants, such as the FcII receptor, play
important roles as risk factors for meningococcal disease. Com-
plement is required both for meningococcal bactericidal activity
and for opsonophagocytosis (Fijen et al. 2000). Individuals
deficient in both the early and late components of the comple-
ment system are at increased risk for meningococcal disease
(Sjoholm et al. 1982; Fijen et al. 1999; Emonts et al. 2003).
Compared to the general population, these patients usually
experience less severe, more recurrent disease at an older age
with less common serogroups. Ten to 20 % of invasive menin-
gococcal disease in adults is associated with a complement
defect. The mannose-binding lectin (MBL) pathway of comple-
ment activation can be genetically variable and is associated with
difference in susceptibility to meningococcal disease in one third
of all cases (Hibberd et al. 1999). Other genetic polymorphisms
affecting the risk of acquiring meningococcal disease have also
been described (TNF, FcgRIIA, FcgRIII, PAI-1, ACE-1, IL-1Ra,
IL-1b, TLR4) (Stephens et al. 2007).
It is well known that genetic variation in innate immune
response genes contributes to interindividual differences in
meningococcal and pneumococcal disease manifestations
(Sanders et al. 2011). Disappearance of antibody acquired
from the mother increases the risk for infants and young chil-
dren. For example, homozygotes for codon variants in the man-
nose-binding lectin, an important mediator of host innate
immunity, representing about 5 % of north Europeans and
North Americans and larger proportions of populations in
many developing countries, have a substantially increased risk
of invasive pneumococcal disease (Roy et al. 2002). In contrast,
little is known about genetic variation affecting susceptibility to
pneumococcal meningitis, but polymorphisms in Toll-like
receptors 2, 4, and 9 were recently linked to hearing loss in
patients who survived meningococcal or pneumococcal menin-
gitis (van Well et al. 2012).
Polymorphisms in genes coding for the Fcg-receptor II
(CD32), Fcg-receptor III (CD16), mannose-binding lectin, and
TLR4 are associated with increased risk (Hibberd et al. 1999;
Fijen et al. 2000; Read et al. 2001; Smirnova et al. 2003; Faber
et al. 2006; Tully et al. 2006). Mannose-binding lectin is a plasma
opsonin that initiates complement activation; specific polymor-
phisms in this gene are enriched in children with meningococcal
disease relative to controls (Hibberd et al. 1999). Expression of
plasminogen activator inhibitor (PAI-1) affects severity and
mortality of meningococcal sepsis, suggesting that impaired
fibrinolysis is an important factor in the pathophysiology of
meningococcal sepsis (Emonts et al. 2003). Meningococcal
disease is occasionally linked to immune suppressive disorders
such as the nephrotic syndrome, hypogammaglobulinemia,
splenectomy, and HIV/AIDS (10-fold increased risk for spo-
radic disease vs 100-fold increased risk for infection with the
pneumococcus or meningococcus in HIV/AIDS). However, the
risk of an epidemic outbreak of meningococcal disease in coun-
tries with high rates of HIV does not appear to be elevated.
Congenital and acquired antibody deficiencies, and possibly
blocking of IgA immunoglobulin, also increase risk.
Opsonization and phagocytic function are important host
defense mechanisms that influence disease incidence as well;
for example, pp[as shown by disease reduction after polysaccha-
ride vaccination in individuals with complement deficiencies.
Rapidly progressive, fatal meningococcemia can arise in patients
deficient in properdin (Sjoholm et al. 1982), and there is
a significant increased risk of recurrent meningococcal infec-
tions for those with defects in the terminal complement pathway
(C5–C9) (Fijen et al. 1999).
Epigenetic Cofactors. There is limited knowledge concerning
the cofactors that influence the spread and severity of meningo-
coccal and pneumococcal disease. Low absolute humidity can
damage the nasopharyngeal mucosa, allowing meningococci to
pass the mucosal barrier more easily or be transmitted by
coughing. In countries with a temperate climate, susceptibility
to meningococcal and pneumococcal disease is highest in the
winter when absolute humidity is low. There is also evidence
that viral (influenza) and mycoplasma respiratory infections can
predispose to meningococcal and pneumococcal disease,
perhaps by damaging mucosal surfaces; altering dynamics of
adherence, colonization, and spread; and impairing mucosal
immunity. The role of mucosal immunity in preventing
or enhancing meningococcal disease requires more analysis in
the future.
The association between HIV and meningococcal disease is
not well studied. Population-based studies in the USA indicate
an increased risk (7-fold) (Stephens et al. 1995), but this has
not been noted for African outbreaks. However, the high prev-
alence of HIV in African and Asian countries might influence
Meningitis 18 417
carriage or susceptibility to and severity of meningococcal disease,
as demonstrated for pneumococcal infections.
Therapy and Management
Antimicrobial Treatment of Meningococcal
and Pneumococcal Meningitis
Eradication of the infecting organism from the CSF is entirely
dependent on antibiotics, and bactericidal antibiotics should be
administered intravenously at the highest clinically validated
doses to patients with suspected bacterial meningitis (Tunkel
et al. 2004). Several retrospective and prospective studies showed
that delay in antibiotic treatment was associated with adverse
outcomes (Miner et al. 2001; Auburtin et al. 2006). In patients
with suspected bacterial meningitis for whom immediate
lumbar puncture is delayed due to pending brain imaging
study or the presence of disseminated intravascular coagulation,
blood cultures must be obtained, and antimicrobial treatment
should be initiated immediately. Selection of empirical antimi-
crobial regimens is designed to cover the likely pathogens, based
on age of the patient and specific risk factors, with modifications
if CSF Gram stain is positive.
The recommended treatment for patients who have meningo-
coccal or pneumococcal meningitis is benzylpenicillin or a third-
generation cephalosporin (e.g., ceftriaxone) (Stephens et al. 2007).
For most cases of uncomplicated bacterial meningitis, 7-day
treatment is adequate. When the etiology is not known at
admission, ceftriaxone or cefotaxime is used for the first
24–48 h to cover the possibility of other bacterial pathogens
(Stephens et al. 2007). Beta-lactamase-producing strains have
occasionally been recovered, harboring a penicillinase-encoding
plasmid. In addition, there are N.meningitidis strains that are
not b-lactamase positive, but have decreased sensitivity to
penicillin due to reduced affinity of penicillin to penicillin-
binding proteins 2 and 3, resulting from an altered penA gene
(Spratt et al. 1989; Bowler et al. 1994). Studies have reported
isolates of S.pneumoniae with penicillin MICs of 0.12–1.0 mg/
mL that had mutations in the target penicillin-binding proteins
(Spratt et al. 1989; Bowler et al. 1994; Dowson et al. 1989).
Similarly, penicillin has been the standard treatment for
meningococcal meningitis, but penicillin resistance has evolved,
with an implication of treatment failures. An increased
incidence in penicillin non-susceptible strains of N.meningitidis
(e.g., MICs 0.1–0.5 mg/mL) from 9.1 % in 1986 to 81.4 % in
Spain and South America (Latorre et al. 2000; Ibarz-Pavon
et al. 2012). By contrast, relative resistance to penicillin
(MIC 0.1 mg/mL) has been shown to occur in 3–4 % of the
meningococcal isolates in the USA and in 2 % of the 137 isolates
recovered between 2000 and 2006 from equatorial sub-Saharan
Africa (Brigham and Sandora 2009). These findings support the
use of a third-generation cephalosporin for meningococcal
meningitis in areas where penicillin resistance is prevalent,
at least until penicillin susceptibility is known. Although the
frequency of relatively penicillin-resistant meningococci is low,
continued surveillance is necessary. Cefotaxime or ceftriaxone is
used when relatively penicillin-resistant strains are isolated.
The ability of an antimicrobial agent to penetrate the blood–
brain barrier is the most important factor that determines
whether efficient bacterial killing in the CSF will happen.
Blood–brain barrier penetration is affected by lipophilic prop-
erty, molecular weight, and protein-binding ability of drugs,
inflammation of the meninges, water transport, and efflux
transporters (Loscher and Potschka 2005). Lipophilic agents
(i.e., fluoroquinolones and rifampicin) penetrate relatively well
into the CSF even if the meninges are not inflamed, whereas
hydrophilic agents (i.e., b-lactams and vancomycin) have
decreased penetration into CSF in the absence of meningeal
inflammation (Ahmed et al. 1999). An important factor in the
choice of empirical antimicrobial agents is the emergence of
antimicrobial-resistant organisms, including N.meningitidis
and S.pneumoniae that is resistant to penicillin or third-
generation cephalosporins, and Gram-negative bacilli that are
resistant to many b-lactam drugs. For example, the prevalence of
S.pneumoniae strains that are relatively resistant to penicillin
(minimum inhibitory concentration [MIC] 0.1–1.0 mg/mL) or
highly resistant to penicillin (MIC greater than 1.0 mg/mL) is
increasing, and many of the penicillin-resistant pneumococci
have reduced susceptibility to third-generation cephalosporins
(i.e., cefotaxime and ceftriaxone) (Tunkel et al. 2004). Treatment
failures in bacterial meningitis as a result of multiresistant
organisms have been reported (John 1994). Therefore, empirical
treatment for patients with bacterial meningitis in areas where
resistant S.pneumoniae strains are prevalent must include the
addition of vancomycin. However, penetration of vancomycin
into the CSF can be reduced in the absence of meningeal inflam-
mation and also in patients who receive adjunctive dexametha-
sone treatment.
Before passive immune or antibiotic treatment was available,
the mortality of systemic meningococcal and pneumococcal
disease was 70–90 %. The case fatality rate is now around 10 %
in many countries. However, early recognition by parents and
health professionals of the importance of fever and headache
with a non-blanching rash (the glass test), prehospital antibiotic
treatment, rapid transportation to a local hospital, and stabili-
zation in an intensive care unit has substantially reduced the case
fatality rate in children (Levy et al. 1990; Borchsenius et al.
1991). For patients in intensive care, recognition of the different
pathophysiological processes associated with meningococcal
meningitis (which causes death predominantly by cerebral
edema) and meningococcal septic shock (which causes death
predominantly through hypovolemia, capillary leak, myocardial
dysfunction, and multiorgan failure) has led to major changes in
treatment and management strategies for these two different
forms of disease (Stephens et al. 2007; Brandtzaeg and van
Deuren 2012). Aggressive management of raised intracranial
pressure reduces mortality.
Prehospital antibiotic treatment is advocated in many coun-
tries, to reduce the case fatality rate for patients with fulminant
meningococcal or pneumococcal disease. If antibiotic treatment
is initiated before admission, benzylpenicillin, ceftriaxone, or
418 18 Meningitis
another effective antibiotic should be injected intravenously
or intramuscularly in adults and intramuscularly in children
(Stephens et al. 2007). During epidemics in developing
countries, a single injection of long-acting chloramphenicol
injected intramuscularly can be sufficient treatment for patients
with meningitis, and this simple treatment has saved
many thousands of lives. A single injection of ceftriaxone is
equally effective and could become the preferred treatment
for epidemic meningitis.
Pneumococcal infections have been treated with penicillin
since decades. However, an emerging increase in resistance rates
to penicillin and to other common antibiotics is now being
observed, affecting treatment outcome. So far resistance has
been found to most antibiotic drugs except for vancomycin.
Resistance rates to penicillin and macrolides can be high and
above 50 % in some areas (Prymula et al. 2011). Also, pneumo-
cocci with reduced susceptibility to penicillin often carry
other resistance determinants. In countries with low antibiotic
resistance rates such as Norway and Sweden, pneumococcal
isolates with reduced susceptibility to penicillin are
multiresistant (resistant to more than two antibiotic classes) in
30–60 % of cases. The spread of antibiotic resistance is mainly
due to the spread of successful international clones carrying
resistance traits. The wide use of antibiotics also influences
resistance rates. Milder infections caused by pneumococci with
low MIC values to penicillin can usually be treated with a higher
dose of penicillin. However, pneumococcal meningitis caused by
pneumococci with a reduced susceptibility to penicillin needs to
be treated with other antibiotics than penicillin.
Adjunctive Treatment
Neurological sequelae are common in survivors of meningitis
and include hearing loss, cognitive impairment, and develop-
mental delay. For example, bacterial meningitis has been iden-
tified as the leading postnatal cause of developmental
disabilities, including cerebral palsy and mental retardation
(Kim 2012). Hearing loss happens in 22–30 % of survivors
of pneumococcal meningitis compared to 1–8 % after
meningococcal meningitis (Andersen et al. 1997). In a recent
meta-analysis, adjunctive treatment with dexamethasone was
associated with lower case mortality, and lower rates of severe
hearing loss and long-term neurological sequelae (van de Beek
et al. 2010). The beneficial effect of adjunctive dexamethasone
treatment was also evident in adults with bacterial meningitis.
The outcome of bacterial meningitis has been suggested to
be related to inflammation of the subarachnoid space. Hence,
it has also been suggested that in addition to antibiotics, menin-
gococcal and pneumococcal meningitis can be treated with
corticosteroids. Data in the literature are controversial where
some studies show an effect on sequelae such as hearing loss and
mortality, while others do not.
Dexamethasone given shortly before or when antibiotics
were first given has been shown to reduce the rate of hearing
loss in children with H.influenzae type b meningitis, but its
beneficial effects on hearing and other neurological sequelae are
not as clear against meningitis caused by other organisms (van
de Beek et al. 2010). Dexamethasone treatment might be con-
sidered for infants and children older than 6 weeks with pneu-
mococcal meningitis after considering the potential benefits and
possible risks. There is, however, no evidence from randomized
controlled clinical trials that dexamethasone reduces death
caused by brain edema, which can take place in patients with
meningococcal meningitis. The widespread use of dexametha-
sone in children with bacterial meningitis needs careful moni-
toring of clinical (e.g., fever curve, resolution of symptoms and
signs) and bacteriological responses to antimicrobial treatment,
particularly for patients with meningitis caused by pneumococci
that are resistant to third-generation antibiotics, in whom bac-
teriological killing in the CSF depends on vancomycin. Moni-
toring of the clinical response (e.g., fever curve) can be
complicated by the use of dexamethasone. In addition, concom-
itantly given dexamethasone and vancomycin can reduce
penetration of vancomycin into the CSF by virtue of the anti-
inflammatory activity of dexamethasone, resulting in treatment
failure. However, CSF bactericidal activity has been shown in
children who have meningitis due to cephalosporin-resistant
pneumococci, and such cases should be treated with dexameth-
asone as well as vancomycin and ceftriaxone (Klugman et al.
1995). Another issue with adjunctive dexamethasone treatment
is the possibility of neuronal injury, including hippocampal
apoptosis in experimental animals with pneumococcal menin-
gitis who received dexamethasone (Leib et al. 2003). Long-term
follow-up studies are thus needed to address the effect of dexa-
methasone treatment on any cognitive and neuropsychological
outcomes in patients with bacterial meningitis.
Prevention of Meningococcal
and Pneumococcal Disease
Prevention of meningococcal and pneumococcal disease is based
on chemoprophylaxis and vaccination (Rosenstein et al. 2001).
The advancement of vaccine design in enhancing immunoge-
nicity has been shown to be important in preventing meningitis
caused by N.meningitidis and S.pneumoniae. Protein-
conjugated capsular polysaccharide vaccines have almost
completely eliminated meningitis caused by vaccine serotypes.
Meningococcal Capsular Vaccines. Meningococcal polysac-
charide vaccines reduce the incidence of infection among mili-
tary recruits, reduce the progress of epidemics of serogroup
A disease, and protect susceptible complement-factor-deficient
individuals (Stephens et al. 2007). Capsule polysaccharide vac-
cines are available for the pathogenic meningococcal serogroups
A, C, Y, and W-135. These vaccines are safe with mild local
adverse events and have good efficacy (>85 %) in older children
and adults. However, due to lack of a T-helper response, the
vaccines are poorly immunogenic below 2 years of age, fail to
induce immunological memory, and provide protection for only
3–5 years. Polysaccharide vaccines are used by travelers visiting
countries with a high incidence of meningococcal disease.
Meningitis 18 419
A polysaccharide vaccine against serogroup B meningococci is
not available due to carbohydrate mimicry and poor
Capsular polysaccharide vaccines to decrease A, C, Y, and W-
135 meningococcal disease were introduced in the 1970s and
1980s on the basis of Gotschlich, Gold, Goldschneider, and
Artenstein’s classic studies (Snape and Pollard 2005). These
vaccines are safe with mild local adverse events, are effective
(>85 %) in children (older than 2 years) and adults, but are
less immunogenic (C less than A) in children younger than 24
months. Immunity to the polysaccharide vaccines is limited to
3–5 years of protection, and immunological hyporesponsiveness
is induced by repeated doses of the group C and possibly group
A polysaccharides. Polysaccharide vaccines do not induce
immunological memory and have little or no effect on nasopha-
ryngeal carriage. Despite their limitations, meningococcal poly-
saccharide vaccines have been used extensively to control
epidemics in countries of the African meningitis belt, and they
have saved many lives. However, they have often been deployed
too late in the course of an outbreak to achieve maximum effect.
A major advance in the prevention of meningococcal disease
has been the development of meningococcal polysaccharide and
protein conjugate vaccines and their introduction into the UK,
other parts of Europe, Canada, and the USA (Snape and Pollard
2005; Borrow 2012). These vaccines are safe and immunogenic
in young children, induce immunological memory, and decrease
nasopharyngeal carriage of meningococci. In the UK, introduc-
tion of the C conjugate meningococcal vaccines in 2000 to all
children and young adults greatly reduced the rate of serogroup
C disease (90 % vaccine effectiveness at 3 years for patients aged
11–18 years) (Vipond et al. 2012). A major protective effect of
the C conjugate vaccine is mediated through herd immunity.
Rates of serogroup C carriage and disease in non-vaccinated
individuals are reduced by more than 50 %. However, the
three-dose schedule of group C immunization in infancy orig-
inally used in the UK provided only transitory protection, and
a booster dose or alternative immunization schedule was
needed. Thus, the UK has changed to a schedule of two doses
of meningococcal C conjugate vaccine given at 3 and 4 months
of age, followed by a booster at 12 months. In the Netherlands,
meningococcal C conjugate vaccination is not started until the
second year of life. A serogroup A, C, Y, and W-135 polysaccha-
ride-conjugate meningococcal vaccine has been introduced in
the USA for adolescents (Vipond et al. 2012). In addition to
children and adolescents, populations who should benefit from
the new conjugate vaccines are military recruits, patients with
complement or other immune deficiencies, microbiologists who
are routinely exposed to isolates of N.meningitidis, and people
who travel to or reside in countries where N.meningitidis is
The immunogenicity of polysaccharide vaccines is greatly
improved by chemical conjugation to a protein carrier.
The resulting polysaccharide-conjugate vaccines are safe
and immunogenic in young infants and induce long-term
memory. Conjugate polysaccharide vaccines against serogroups
A, C, W-135, and Y are now available. These vaccines are so far
safe and immunogenic, are anticipated to provide long duration
of protection (as they induce a T-cell-dependent response), and
are effective in young children (Bilukha and Rosenstein 2005).
Introduction of the C conjugate meningococcal vaccines in 2000
markedly reduced the incidence of serogroup C disease in the
UK with estimated vaccine efficacies of 88 % in young children
and 95 % in young adolescents. Immunization also decreased
nasopharyngeal carriage by 66 % and transmission of the path-
ogen (herd immunity) (Snape and Pollard 2005; Vipond et al.
2012). However, widespread use of monovalent serogroup con-
jugate vaccines can become ineffective when the capsule types
switch due to genetic exchange or strains arise that show reduced
capsule expression.
Additional research on meningococcal conjugate vaccines
holds great potential for control of meningococcal disease in
areas (e.g., sub-Saharan Africa) where epidemics are frequent.
A serogroup A conjugate vaccine has been carried out by
a nonprofit organization, the Meningitis Vaccine Program,
which is supported by the Bill & Melinda Gates Foundation
(Borrow 2012; Caugant et al. 2012). The results of the first trials
of this vaccine in Africa are promising, and researchers hope that
this vaccine shortly will be ready for widespread deployment.
A combined pediatric vaccine that contains serogroup A and
C meningococcal conjugates has also been tested in Africa
(Borrow 2012).
Pneumococcal Capsular Vaccines. Year 2000, a pneumococcal
vaccine (PCV7) based on 7 out of the 93 capsular serotypes,
associated to a protein in a so-called conjugated vaccine, was
introduced in the United States. The 7 capsular types (types 4,
6B, 9V, 14, 18C, 19F, and 23F) were chosen because they were the
most prominent causing invasive pneumococcal disease in the
United States. The vaccine introduction led to a decrease of
invasive pneumococcal disease among infants and children
younger than 5 years and also a herd immunity effect in the
adult population (Hsu et al. 2009). Here, Hsu et al. showed
a decline of pneumococcal meningitis in eight sites in the Unites
States between 1998–1999 and 2005 from 1.13 cases to 0.79 cases
per 100, 000. In children younger than 2 years of age and in those
65 years of age or older, the incidence of pneumococcal menin-
gitis decreased by 64 % and 54 % respectively during the study
period. Furthermore, importantly since pneumococcal carriage
is a prerequisite for a pneumococcal invasive disease, a reduction
of vaccine type carriage was observed. Use of these protein-
conjugated vaccines has also reduced H.influenzae type b and
pneumococcal meningitis among unvaccinated populations
through herd immunity. At present, limitations with PCV7
conjugate vaccines include an apparent increase in the incidence
of invasive pneumococcal disease, including meningitis caused
by non-PCV7 serotypes, such as serotype 19A (a penicillin and
third-generation cephalosporin-resistant non-PCV7 serotype),
and an apparent decline in bactericidal antibody against
N.meningitidis in infants, requiring a booster immunization in
the second year of life (Borrow 2012). The conjugated pneumo-
coccal vaccines have now been introduced into the childhood
vaccination program in several countries worldwide, and
a decrease of invasive disease has been noticed in most countries.
420 18 Meningitis
However, recently, it was shown that serotypes not included in
the vaccine are increasing as well as certain lineages harboring
antibiotic resistance determinants (serotype replacement and
serotype shift) (Grijalva and Pelton 2011). An increase has
been seen, for example, of serotype 19A causing invasive disease
and carrying antibiotic resistance markers creating treatment
problems (McGee 2007). In some countries, the decline in
invasive disease has been hampered because of an increase of
non-vaccine types. Moreover, some studies show that the decline
in colonization has been hampered by an increase of non-
vaccine-type carriage (Tocheva et al. 2011). Recently, second-
generation conjugated vaccines including 10 (PCV10 including
also serotypes 1, 5, and 7F) or 13 (PCV13 including in addition
types 3, 6A, and 19A) serotypes have been launched.
Outer Membrane Protein Vaccines. The development of vac-
cines for serogroup B N.meningitidis remains a challenge
(Borrow 2012). The serogroup B capsule has an identical struc-
ture to polysialic structures expressed in fetal neural tissue and
does not induce a protective IgG response. Thus, strategies have
focused on non-capsular antigens such as outer membrane porins
and vesicles and lipooligosaccharides. The diversity of major
outer membrane structures in meningococci has, however, lim-
ited these approaches (Snape and Pollard 2005; Bjune et al. 1991).
Complement-mediated killing of encapsulated strains is also
achieved with cross-reactive antibodies directed against outer
membrane components. Developed outer membrane vesicle
(OMV) vaccines with a low LOS composition show efficacies
of 50–80 % in clinical trials, but do not protect young children
and are in general too strain specific; that is, the vaccines can be
used against clonal disease outbreaks but not for prevention of
sporadic diseases caused by diverse strains. Multivalent vaccine
strains based on common variants of PorA (a major inducer and
target of bactericidal antibodies) may provide protection against
multiple subtypes of N.meningitidis. Recently, novel conserved
candidate vaccine antigens have been identified using a ‘‘reverse
vaccinology’’ approach (Rappuoli 2000; Giuliani et al. 2006;
Palumbo et al. 2012). First, the lipoproteins GNA1870 and
GNA2132; the conserved surface proteins OMP85, NspA, and
NadA; but also PorA, pilin, and LOS conjugates were evaluated
for their vaccine potential. The resulting vaccine, referred to as
the four-component MenB (4CMenB) vaccine, currently con-
tains the OMV (PorA) from the New Zealand vaccine along with
three recombinant proteins identified by reverse vaccinology:
factor H-binding protein (fHbp), neisserial adhesin A (NadA),
and Neisseria heparin-binding antigen (NHBA) (Major et al.
The aim of chemoprophylaxis is to reduce secondary cases of
meningococcal and pneumococcal disease and to arrest out-
breaks. The risk of a secondary case among close contacts in
the household setting is 150–1,000 times higher than that in the
general population. Children are at greatest risk, but secondary
disease can occur at all ages. Risk is maximal in the week
following recognition of the index case but extends for several
Many antibiotics used for therapy do not effectively eradi-
cate or prevent carriage of meningococci because of inadequate
levels in oropharyngeal secretions (Deghmane et al. 2009).
Rifampicin, ceftriaxone, azithromycin, and the quinolones are
effective against meningococci in the naso- and oropharynx
(Stephens et al. 2007). However, rifampicin resistance can
develop rapidly, and quinolone resistance in meningococci has
recently been reported. Ceftriaxone as a single intramuscular
dose is 97 % effective in household contacts 1–2 weeks after
infection. The advantage of ceftriaxone is that it can be used in
pregnancy and in small children.
Chemoprophylaxis can be helpful in the control of localized
outbreaks in residential schools, barracks, etc., but is generally
not recommended for the control of epidemics because of cost
and drug resistance. For example, widespread distribution of
rifampicin would be unwise in communities in which tubercu-
losis is prevalent. Many meningococcal strains are sulfur
resistant (folP mutation), and so sulfur drugs, once highly
effective, can no longer be used for chemoprophylaxis. Rifam-
picin, ceftriaxone, azithromycin, and quinolones all have activity
against meningococci in the nasopharynx. However, resistance
to rifampicin can develop rapidly, and quinolone resistance
in meningococci has been reported (Gorla et al. 2011).
Chemoprophylaxis is sometimes recommended for patients
given penicillin or chloramphenicol for treatment since
pharyngeal carriage may not be eliminated by intravenous
administration of these antibiotics and the patient could remain
colonized with a virulent strain.
Future Challenges and Opportunities
Bacterial meningitis continues to be an important cause of mor-
tality and morbidity throughout the world, with differential risk
for disease among small children, individuals living in low-income
countries, and due to infection with antimicrobial- or multidrug-
resistant pathogen. Vaccination with protein-conjugated
H.influenzae type b, S.pneumococcus PCV, and N.meningitidis
Mencevax ACWY has successfully reduced worldwide incidence
of meningitis; this raises the hope that other conserved
bactericidal epitopes exist and can be identified and exploited
in a similar manner. Unfortunately, conjugated vaccines have so
far been introduced only in the developed world, even though
the highest incidence of meningococcal and pneumococcal
invasive diseases occurs in less affluent countries.
Host receptors and signal transduction pathways involved in
the microbial invasion of the BBB might represent potential
targets for novel therapeutic approaches for meningococcal
and pneumococcal disease (Huang and Jong 2009). Using
a model system that analyzed penetration of the BBB by E.coli,
a proof-of-concept study suggested that the HBMEC receptor
for CNF1 (RPSA) and cytosolic phospholipase A2amight
represent such ‘‘druggable’’ targets, at least for E.coli,
but potentially also for meningococci and pneumococci
Meningitis 18 421
(Plant et al. 2006; Orihuela et al. 2009). Other studies suggest
that the cell-wall component lipoteichoic acid is a pattern rec-
ognition molecule and inflammatory mediator that plays a role
in pneumococcal disease; however, the identity of the receptor
for lipoteichoic acid remains controversial. Interestingly, intra-
thecal treatment with antibodies that recognize phosphor-
ylcholine, teichoic acid, and lipoteichoic acid was effective in
reducing neuronal damage in experimental pneumococcal
meningitis (Gerber et al. 2012).
Basic understanding of the molecular mechanisms of
meningococcal and pneumococcal pathogenesis is still lacking
and is urgently needed to support advances on novel therapeutic
and preventive approaches for meningitis. Such basic research
will enhance our understanding of bacterial emergence,
pathogenic genome structure, horizontal genetic exchange, and
innate and adaptive immune responses. N.meningitidis and
S.pneumoniae are valuable low-complexity model organisms
for such studies, at least in part because they only colonize and
infect human beings. Further studies of the genetics and patho-
genicity of N.meningitidis and S.pneumoniae should reveal
much about how they evolved, spread worldwide, and how
and why they cause disease only in humans. This research is
important in the quest to define fundamental mechanisms of
microbial pathogenesis and to facilitate design of novel strategies
for managing emerging or reemerging microbial threats.
In summary, earlier clinical recognition and more effective
treatment of meningococcal and pneumococcal disease will be
critical to further reduce morbidity and mortality associated
with these diseases. Improved understanding of the pathophys-
iology of infection by meningitis-causing bacteria will
undoubtedly lead to innovative new approaches for the
management also of patients with meningococcal and
pneumococcal septicemia, which could further reduce case
fatality and/or case morbidity. The ultimate control of menin-
gococcal and pneumococcal disease will require widespread and
expanded use of effective vaccines. Worldwide surveillance, the
expanded use of polysaccharide-conjugate vaccines, and the
development of broadly effective serogroup B vaccines could
eliminate N.meningitidis and S.pneumoniae as major threats
to human health in industrialized countries within the next
decade. However, strong, sustained, and coordinated
support will be needed from the international community, if
meningococcal and pneumococcal disease is to be controlled in
Africa and other developing areas, where the infection poses the
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