Article

Complement Inhibitors from Scabies Mites Promote Streptococcal Growth – A Novel Mechanism in Infected Epidermis?

George Washington University, United States of America
PLoS Neglected Tropical Diseases (Impact Factor: 4.45). 07/2012; 6(7):e1563. DOI: 10.1371/journal.pntd.0001563
Source: PubMed

ABSTRACT

Scabies is highly prevalent in socially disadvantaged communities such as indigenous populations and in developing countries. Generalized itching causes discomfort to the patient; however, serious complications can occur as a result of secondary bacterial pyoderma, commonly caused by Streptococcus pyogenes (GAS) or Staphylococcus aureus. In the tropics, skin damage due to scabies mite infestations has been postulated to be an important link in the pathogenesis of disease associated with acute rheumatic fever and heart disease, poststreptococcal glomerulonephritis and systemic sepsis. Treatment of scabies decreases the prevalence of infections by bacteria. This study aims to identify the molecular mechanisms underlying the link between scabies and GAS infections.
GAS bacteria were pre-incubated with blood containing active complement, phagocytes and antibodies against the bacteria, and subsequently tested for viability by plate counts. Initial experiments were done with serum from an individual previously exposed to GAS with naturally acquired anti-GAS antibodies. The protocol was optimized for large-scale testing of low-opsonic whole blood from non-exposed human donors by supplementing with a standard dose of heat inactivated human sera previously exposed to GAS. This allowed an extension of the dataset to two additional donors and four proteins tested at a range of concentrations. Shown first is the effect of scabies mite complement inhibitors on human complement using ELISA-based complement activation assays. Six purified recombinant mite proteins tested at a concentration of 50 µg/ml blocked all three complement activation pathways. Further we demonstrate in human whole blood assays that each of four scabies mite complement inhibitors tested increased GAS survival rates by 2-15 fold.
We propose that local complement inhibition plays an important role in the development of pyoderma in scabies infested skin. This molecular link between scabies and bacterial infections may provide new avenues to develop alternative treatment options against this neglected disease.

Complement Inhibitors from Scabies Mites Promote
Streptococcal Growth A Novel Mechanism in Infected
Epidermis?
Angela Mika
1
, Simone L. Reynolds
1,2
, Darren Pickering
1
, David McMillan
1
, Kadaba S. Sriprakash
1
,
David J. Kemp
1
, Katja Fischer
1
*
1 Infectious Diseases Program, Biology Department, Queensland Institute of Medical Research, Herston, Brisbane, Australia, 2 School of Veterinary Sciences, The University
of Queensland, Gatton, Australia
Abstract
Background:
Scabies is highly prevalent in socially disadvantaged communities such as indigenous populations and in
developing countries. Generalized itching causes discomfort to the patient; however, serious complications can occur as a
result of secondary bacterial pyoderma, commonly caused by Streptococcus pyogenes (GAS) or Staphylococcus aureus. In the
tropics, skin damage due to scabies mite infestations has been postulated to be an important link in the pathogenesis of
disease associated with acute rheumatic fever and heart disease, poststreptococcal glomerulonephritis and systemic sepsis.
Treatment of scabies decreases the prevalence of infections by bacteria. This study aims to identify the molecular
mechanisms underlying the link between scabies and GAS infections.
Methodology/Principal Findings:
GAS bacteria were pre-incubated with blood containing active complement, phagocytes
and antibodies against the bacteria, and subsequently tested for viability by plate counts. Initial experiments were done
with serum from an individual previously exposed to GAS with naturally acquired anti-GAS antibodies. The protocol was
optimized for large-scale testing of low-opsonic whole blood from non-exposed human donors by supplementing with a
standard dose of heat inactivated human sera previously exposed to GAS. This allowed an extension of the dataset to two
additional donors and four proteins tested at a range of concentrations. Shown first is the effect of scabies mite
complement inhibitors on human complement using ELISA-based complement activation assays. Six purified recombinant
mite proteins tested at a concentration of 50
mg/ml blocked all three complement activation pathways. Further we
demonstrate in human whole blood assays that each of four scabies mite complement inhibitors tested increased GAS
survival rates by 2–15 fold.
Conclusions/Significance:
We propose that local complement inhibition plays an important role in the development of
pyoderma in scabies infested skin. This molecular link between scabies and bacterial infections may provide new avenues to
develop alternative treatment options against this neglected disease.
Citation: Mika A, Reynolds SL, Pickering D, McMillan D, Sriprakash KS, et al. (2012) Complement Inhibitors from Scabies Mites Promote Streptococcal Growth A
Novel Mechanism in Infected Epidermis? PLoS Negl Trop Dis 6(7): e1563. doi:10.1371/journal.pntd.0001563
Editor: Gary L. Simon, George Washington University, United States of America
Received October 27, 2011; Accepted January 27, 2012; Published July 17, 2012
Copyright: ß 2012 Mika et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by the Australian National Health and Medical Research Council (http://www.nhmrc.gov.au/, program grant 496600, project
grant 613626, and a fellowship to DJK). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: Katja.Fischer@qimr.edu.au
Introduction
The global prevalence of pyoderma from various bacterial
infections has been estimated to exceed 111 million children,
making it one of the most common skin afflictions along with
scabies and tinea [5]. In tropical climates, scabies predisposes to
secondary bacterial skin infections in particular by Streptococcus
pyogenes (group A streptococci, GAS), the causal agent of acute
rheumatic fever and rheumatic heart disease (ARF/RHD). This
association between scabies and pyoderma caused by GAS has
been well established [4]. Globally, GAS associated diseases, such
as RHD, acute post-streptococcus glomerulonephritis (APSGN)
and severe invasive diseases, affect an estimated 18 million
individuals and account for over 0.5 million deaths per year [6]. In
Australian Aboriginal communities RF/RHD prevalence has
steadily risen to almost 2% in 2008 [7], translating to the highest
incidences reported globally. Scabies and pyoderma have also
been linked with outbreaks of APSGN [4]. In remote Aboriginal
communities more than 70% of the children below two years of
age have presented with scabies and skin sores, respectively [8].
Community-wide treatment of scabies decreases pyoderma [9,10],
which suggests a key role of the burrowing mite.
Mechanical disruption of the stratum corneum caused by mites
and host scratching may be considered a primary prerequisite
promoting secondary skin infections; however contributing mo-
lecular interactions between host, parasites and bacteria have not
been investigated. An immediate, non-specific epidermal host
defense mechanism against microbes is the local activation of the
complement system [11]. Phagocytes migrate to the site of
infection and attempt to engulf and dispose of the invading
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organisms with the help of available antibodies and complement,
both present in the host’s serum, [12]. We have recently
established that scabies mites express extensive complement
evasion machinery disrupting the three complement pathways at
several levels. Two members of a large family of catalytically
inactive serine protease paralogues termed SMIPP-Ss [13,14]
inhibit all three pathways of human complement [15]. Further-
more two scabies mite serpins (SMSs) also function as effective
complement inhibitors, each binding to a range of complement
factors on several levels of the three complement pathways [16].
While the in vivo concentrations of these mite complement
inhibitors excreted into the confined space of the burrows have
not been determined, cumulative effects of multiple anti-comple-
ment activities can be expected. A logical question to ask is
whether this increased level of anti-complement activity has an
effect on the bacteria that colonize the burrows. Here we present a
set of in vitro data focusing on two SMIPP-Ss and two SMSs, which
indicate that under physiological conditions there is indeed a
considerable effect on the growth of Streptococcus pyogenes.
Methods
Ethics statement
Normal human serum for complement activation assays and
whole blood samples for bactericidal assays were prepared from
blood donated by healthy volunteers after informed consent and in
accordance with the principles in ethical conduct as stated in the
‘‘National Statement on Ethical Conduct in Human Research’’,
documented by the Australian National Health and Medical
Research Council.
Cloning
Five scabies mite inactive serine protease paralogues (SMIPP-S
D1, GenBank accession no. AY333085, SMIPP-S I1, AY333081;
SMIPP-S B2, AY333073; SMIPP-S G2, JN167504 and SMIPP-S G4,
AY333078;) were cloned into Pichia pastoris KM71H using vector
pPICZaA (Invitrogen) as described earlier [15]. Two scabies mite
serpins (SMSs; SMSB3a, cDNA clone Yv7088B02; GenBank
accession no. JF317220; SMSB4, cDNA clone Yv5004A04, Gen-
Bank accession no. JF317222) were amplified on cDNA libraries
made from human scabies mites Sarcoptes scabiei [17,18] and cloned
into the pQE9 expression vector (Qiagen) [16].
Heterologous expression and purification of SMIPP-Ss
and SMSs
Recombinant SMIPP-S proteins were expressed in P. pastoris as
secreted proteins and purified as described earlier [15]. Briefly,
mature SMIPP-S protein secreted from P. pastoris was purified
from the expression culture supernatant by hydrophobic interac-
tion chromatography on a 5 ml HiTrap phenyl-Sepharose column
(GE Healthcare) followed by dialysis and ion chromatography on a
5 ml HiTrap SP Sepharose FF column (GE Healthcare).
Recombinant SMS proteins were expressed in E. coli and purified
under denaturing conditions from thoroughly washed and
solubilised inclusion bodies by nickel immobilized metal affinity
chromatography (Qiagen). Purified SMS proteins were refolded
for 3 hours in 300 mM L- arginine, 50 mM Tris, 50 mM NaCl
and 5 mM DTT at pH 8.0 for SMSB3 and pH 10.5 for SMSB4.
Refolded SMS proteins were concentrated using an Ultrasette Lab
Tangential Flow Device (10 kDa cut off; PALL Life Sciences),
followed by further concentration in centrifugal filters (Amicon
Ultra, Millipore).
Molecular masses and purity of the purified recombinant mite
proteins were confirmed using SDS-PAGE analysis with silver and
Coomassie blue R-250 staining. Protein concentrations were
determined according to the Bradford method [19]. Prior to the
phagocytosis assays, the recombinant mite proteins were buffer
exchanged into the corresponding assay buffers using Zeba Desalt
Spin columns (Pierce).
Complement activation assays
Human serum complement levels were assessed using a Wieslab
Complement System Screen kit (EuroDiagnostica) according to
the manufacturer’s instructions. Normal human serum was
prepared from blood of eight healthy volunteers after informed
consent. Inhibition of complement by five SMIPP-Ss and one
SMS was measured in a total volume of 100
ml at serum
concentrations of 1%, 1% and 5.5% for the classical, lectin and
alternative complement pathways, respectively. These serum
concentrations represent recommended conditions, under which
each assay is most sensitive to changes. Normal human serum was
pre-incubated for 30 min at room temperature with 50
mg/ml of
purified scabies mite protein before addition to the ELISA
microtiter plate and immunodetection of the terminal membrane
attack complex (MAC, C5b-9). Absorbance was measured at a
wavelength of 405 nm on a POLARstar Optima fluorescent
microtiter plate reader (BMG Labtech, Melbourne, Australia).
The absorbance obtained in the absence of SMIPP-Ss was defined
as 100%.
Bacterial strain
S. pyogenes (GAS strain 2967, emm-type emm 1) was originally
isolated from a patient with APSGN in Townsville, Queensland,
Australia.
Bacterial growth in human whole blood
Informed consent was obtained from all blood donors. The
initial set of phagocytosis assays was performed using blood from
an individual previously exposed to GAS (D1) with a robust type-
specific immune response to the GAS strain 2967.
Author Summary
Australian Aborigines experience streptococcal invasive
diseases at a five times greater rate than the general
Australian population [1], contributing to an estimated life
expectancy gap of currently 13 years [2] with infectious
diseases being the major cause in remote areas. Alterna-
tive approaches to control skin infection and associated
complications in Aboriginal communities are imperative
[3]. A clear link between scabies and bacterial pyoderma
has been recognised as an underlying factor of Aboriginal
cases of rheumatic fever and heart disease (RF/RHD), skin
sepsis and renal disease [4]. Aiming to elucidate the causal
molecular mechanisms we identified multiple scabies
intestinal protein families functioning as inhibitors of
human complement pathways, thereby preventing com-
plement-mediated gut damage. The work presented here
is at the forefront of a new agenda, looking at the
interactions between scabies mites, bacteria and the host.
We show that scabies mite proteins act as complement
inhibitors and enhance GAS growth in whole blood assays,
presumably by inhibition of host innate immunity. Based
on this groundwork data we hypothesize that the
complement-inhibitory functions of excreted gut mole-
cules promote the growth of bacterial pathogens in the
microenvironment of the epidermal burrows.
Mite Complement Inhibitors Promote GAS Growth
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The standardized phagocytosis assays used blood from ‘‘non-
immune’’ human donors who did not exhibit type-specific
immunity to GAS 2967. Among several donors tested in
preliminary experiments, blood from most donors allowed growth
of the GAS strain, and blood from two such donors was used in
each set of phagocytosis experiments (D2 and D3). To reduce
differences in bacterial growth based on differences in anti-GAS
antibody levels of individual whole blood donors, bactericidal
assays were standardized for donors without or with low levels of
naı
¨
ve anti-GAS IgG by addition of antibodies from a donor
previously exposed to GAS (D1). Immediately prior to use added
antibody sera were heat-inactivated at 56uC for 15 min to abolish
complement activity.
The initial set of bactericidal assays was performed with human
whole blood collected in a standard BD vacutainer (Becton,
Dickinson and Company), using sodium heparin as anticoagulant
at a concentration of 15 USP Units/ml. Comparison of heparin-
versus hirudin-treated blood in bactericidal assays confirmed
earlier findings [20] that the anticoagulant heparin can alter
complement activation, thereby affecting bacterial survival. Thus,
further bactericidal assays were carried out using hirudin
(lepirudin) as anticoagulant, at a concentration of 25
mg/ml
(Dynabyte Informationssysteme GmbH, Munich, Germany).
The assays were performed as described previously [21] with
modifications. Bacteria were grown overnight without agitation at
37uC in 5 ml Todd-Hewitt Broth (THB). A dilution of this pre-
culture was grown in THB with agitation to early exponential
growth phase (OD
600
0.1), and then diluted in PBS to 10
22
or 10
23
,
representing on average 6610
3
colony forming units (CFU) per ml.
Per assay 100
ml human venous blood, 12.5 ml antibody serum,
which was heat-inactivated for 15 min 56uC in a water bath, 15
ml
of scabies mite protein as complement inhibitor or BSA as negative
control (final concentration 25–400
mg/ml) in GVB
2+
buffer (5 mM
veronal, pH 7.35, 140 mM NaCl, 0.1% (w/v) gelatin, 1 mM
MgCl
2
, 0.15 mM CaCl
2
) and 12.5 ml bacteria (containing on
average approximately 75 CFU) were added to a total volume of
140
ml. Assays were placed on a rotisserie and incubated by end
over end mixing for 3 h at 37uC. Subsequently 50
ml aliquots from
each tube were plated in duplicate on 2.5% (v/v) defibrinated
horseblood THB agar (Equicell, Australia) using the pour plate
method and incubated overnight at 37uC for enumeration of CFU.
Bacteria growth may vary between assays performed on different
occasions and between different donors. Hence the percentage
difference in bacterial growth was calculated by comparing CFU
recovered after addition of scabies mite proteins against CFU
recovered from buffer controls at the same time points in individual
experiments. Individual assays were performed in duplicates and
repeated independently between 4 and 12 times.
Statistical analysis
Statistical significance was determined using t tests (GraphPad
Prism software, version 5.0; GraphPad Software Inc. USA).
Values of p,0.05 were considered significant.
Results
SMIPP-Ss and SMSs inhibit all three human complement
activation pathways
A simple method comprising three ELISAs, originally devel-
oped to screen for complement deficiencies [22], was employed to
confirm the complement-inhibitory properties of the recombinant
mite molecules investigated here. The assays were performed with
normal human serum and detection of activation was determined
as the incorporation of C9 into the terminal membrane attack
complex. In this system six purified recombinant mite proteins
(five SMIPP-Ss and one SMS) at a final concentration of 50
mg/ml
inhibited all three complement activation pathways (Figure 1).
Standardization of whole blood bactericidal assays to
test the effect of SMIPP-Ss and SMSs on bacterial survival
Prior to phagocytosis assays samples from three individuals (D1,
D2, D3) were assessed for activation of the classical and alternative
pathways by ELISA for detection of the deposition of C5b-C9, i.e.
the terminal complement membrane attack complex. The
complement activation levels from the three donors were similar
to those of pooled normal human serum (Figure 2a), thereby
validating the suitability of the donors.
In whole blood bactericidal assays heparin treated blood
samples resulted in recovery of fewer GAS colonies than samples
from the same donor treated with hirudin (Figure 2b). This
confirmed earlier findings that the anticoagulant heparin can alter
complement activation, while hirudin (lepirudin) generally pre-
served the complement reactivity, making it more suited for in-vitro
studies [20,23]. Thus, further bactericidal assay analysis was
carried out using hirudin.
We aimed to investigate the effect of mite complement
inhibitors on bacterial growth in blood from several donors,
however most individuals tested did not show a type-specific
immune response to the GAS strain 2967 (data not shown). To
determine whether blood from ‘‘non-immune’’ donors (i.e. blood
that did not contain type-specific opsonizing antibodies) was
suitable, assays were conducted with or without the addition of
such antibodies. Assays testing one SMIPP-S and one SMS at a
concentration of 200
mg/ml generally resulted in increased
bacterial growth; however, the most striking effects of mite
proteins were seen in the presence of strain specific antibodies.
One exemplary set of these results is shown in Figure 2c.
Testing the effect of SMIPP-Ss and SMSs on bacterial
survival in whole blood assays
Initial experiments were performed with plasma from an
individual (D1) previously exposed to GAS and thus with a robust
type-specific immune response to the GAS strain. A dramatic
increase in the bacterial growth ranging from over 200 to almost
1500% was seen in the presence of SMSB3 (200
mg/ml), SMSB4
(25
mg/ml) and SMIPP-S I1 (200 mg/ml), compared to no effect of
BSA (200
mg/ml), indicating that the mite proteins efficiently
interfered with bacterial uptake by human phagocytes (Figure 3a).
As it was difficult to recruit further blood donors with high
antibody titers, whole blood from non-exposed human donors was
used and supplemented with a standard dose of heat-inactivated
human sera previously exposed to GAS (D1). This allowed an
extension of the dataset to two additional donors (D2 and D3) and
four proteins, tested at a range of concentrations. Similarly to what
was observed in the immune-competent donor, the presence of each
scabies mite complement inhibitor increased bacterial survival rates
considerably in a dose dependent manner (Figure 3b). The highest
increases ranged from 200–300% for SMSB3, 400–600% for
SMIPP-S I1 to over 1000% for SMSB4 and SMIPP-S D1, while
bacterial growth was unchanged when the same amount of BSA
bovine serum albumin was added instead.
Discussion
We have previously demonstrated that two SMIPP-Ss are
potent inhibitors of the human complement system, interfering
with all three pathways of the complement cascade [15]. To assess
the effect of additional mite molecules on complement, a microtiter
Mite Complement Inhibitors Promote GAS Growth
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Figure 1. Inhibition of human complement by excretory mite proteins. Shown are the effects of five recombinant, purified SMIPP-Ss (I1, D1,
B2, G2, G4) and one SMS (B3) on the Classical (CP), Lectin (LP) and Alternative (AP) pathways of the human complement system. In ELISA-based
complement activation assays 50
mg/ml of each recombinant protein showed strong complement inhibition. Data presented were obtained in
triplicates and is representative for three to five independent experiments for each mite protein. Shown is the percentage of complement activity as
the mean 6 SD.
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plate-based deposition assay was performed in which complement
activation was initiated by specific ligands for each pathway. After
addition of human serum, pre-treated with the purified recombi-
nant mite proteins, deposited complement proteins were detected
using specific Abs against the terminal membrane attack complex
(MAC, C5b-9). We showed that three further SMIPP-Ss from
additional clades within the phylogenetic tree of the SMIPP-S
family [14] and one scabies mite serpin expand the set of
complement-inhibiting mite proteins, as these also prevent activa-
tion of all complement pathways in these ELISA-based functional
assays. All SMIPP-Ss and SMSs investigated to date were previously
localized by immunohistology [16,24]. All are secreted into the mite
gut and subsequently excreted as components of feces into the
confined space of the mite burrows within the upper epidermal
layers of the human skin. Taken together, the mite produces an
astonishing repertoire of complement inhibitors to prevent comple-
ment activation within the mite gut and in its vicinity. While
complement factors C1q and C9 are localized within the mite
digestive system, the terminal complement MAC formation was not
detectable in the mite gut, indicating that this anti-complement
machinery may be very efficient in vivo [25]. By inference, such a
situation favors secondary infections by bacterial pathogens and
indeed, bacterial lawns are found to coat the mite burrows and
gram-positive cocci have been isolated from mite fecal pellets [26].
We now argue that effective inactivation of complement by
these scabies derived complement inhibitors may aid in efficient
growth of GAS in the microenvironment of the burrows. We
tested this in whole blood bactericidal assays employing functional
human phagocytes and complement. We found that the presence
of each of the four representatively chosen scabies proteins
enhanced growth of GAS in these assays. Three individuals with
normal activation levels of the two dominant complement
pathways (CP and AP, Figure 2a), which were previously shown
to be required for innate immunity to S. pyogenes [27], were
recruited as human blood donors. Generally, mite complement
inhibitors enhanced bacterial growth in GAS bactericidal assays
using naı
¨
ve donor blood, with or without added antibodies specific
to the GAS strain used. However, the most striking effects of mite
molecules were seen when strain specific antibodies were present.
Growth of GAS in the presence of blood from donor D1, with a
robust type-specific immune response to the GAS strain 2967, was
significantly increased in the presence of SMIPP-S I1, SMSB3 and
SMSB4. These results were similar with blood from donors (D2
and D3), who did not exhibit type-specific immunity to GAS 2967.
A standardized assay, using naı
¨
ve blood from donors D2 and D3
allowed testing of four mite proteins at a range of concentrations.
These experiments showed dose dependent bacterial growth.
Notably, the effects of some of the mite complement inhibitors
tested in this system were most dramatic at concentrations below
100
mg/ml, which may be more relevant in a physiological
context. Moreover, additive effects of multiple mite proteins
accumulated in fecal pellets within the human skin burrows would
be expected to cause strong local complement inhibition and may
play an important role in vivo. Under physiological conditions the
increase in bacterial survival may occur at relatively low
concentrations of individual mite complement inhibitors.
This is the first molecular study suggesting a mechanism that may
contribute to the positive association between scabies and GAS skin
Figure 2. Assessment of donor blood and the role of anticoagulant and antibody levels in bactericidal assays. (a) The three human
whole blood donors used in this study showed average complement activation levels representative of the normal population. Complement
activation of the Classical (CP) and Alternative (AP) pathways was determined by ELISA. Shown are means 6 SEM of n = 2 independent experiments,
each performed in duplicate. NHS P(2), inactivated; NHS P(+), active normal human serum (n = 8 donors); D1–D3, individual active serum donors. (b)
Effect of anticoagulant on human whole blood bactericidal assays. Comparison of heparin- and hirudin-treated blood in bactericidal assays indicates
that the anticoagulant heparin can alter complement activation at low concentrations, thereby affecting GAS growth. 6AB, with and without
addition of heat-inactivated anti-GAS sera containing type-specific antibodies; (c) Scabies mite proteins enhance bacterial growth in GAS bactericidal
assays under all conditions tested. Protein concentrations of 200
mg/ml were used. Shown are means 6 SEM of n = 4 experiments from one
representative blood donor with low naı
¨
ve levels of anti-GAS antibodies. 6AB, with and without addition of heat-inactivated anti-GAS sera; hep,
heparin; hir, hirudin. *, p,0.05; **, p,0.01; ***, p,0.001 by t test (GraphPad Prism software).
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infection. We propose that the collective complement-inhibitory
function of multiple scabies mite excretory proteins in combination
with complement inhibitors produced by GAS [28] promote the
survival of bacterial pathogens in the microenvironment of the
epidermal burrows (Figure 3c). Their co-localization and our
demonstration of their interactions clearly establish the potential
worth of a concerted intervention against scabies in the control of
secondary bacterial skin infections. These scabies mite proteins may
present themselves as new targets for protective intervention at the
onset of disease, both scabies and associated pyoderma.
As pyoderma is a condition caused by a combination of bacteria
species, extending the ground-breaking studies presented here to
further pathogens is imperative. Similar studies on Staphyococcus aureus
are currently underway and show comparable preliminary data (not
shown). Another important step will be to demonstrate the effect of
mite molecules in an in vivo setting. Our group has developed a
tractable experimental scabies porcine model [29]. We aim to study
pyoderma development in vivo and to investigate the synergism between
scabies mites and pathogenic bacteria in complement inhibition.
Our results strongly suggest that the misnomer ‘‘itch-mite’’
trivializes an important component of an increasingly urgent
public health issue worldwide. More clinical emphasis should be
given to the scabies component in controlling pyoderma in tropical
settings. Understanding the biological relationship between host,
mites and bacteria in vivo will promote the development of novel
preventive and therapeutic strategies to control scabies and
associated bacterial disease, likely translating into changes of
policy and practice.
Acknowledgments
We thank Yonghong Zhou for technical assistance.
Author Contributions
Conceived and designed the experiments: AM SLR DM KSS DJK KF.
Performed the experiments: AM SLR DP KF. Analyzed the data: AM DM
KSS DJK KF. Contributed reagents/materials/analysis tools: KSS DJK
KF. Wrote the paper: AM KSS DJK KF.
Figure 3. Scabies mite complement inhibitors enhance group A streptococcal growth in human whole blood. (a) Increased GAS growth in
whole blood from a human donor with a type-specific immune response to the GAS strain investigated (D1) in presence of SMSB4 [25
mg/ml], SMSB3, SMIPP-S
I1 or BSA [200
mg/ml]. Shown are means 6 SEM (n = 4 experiments). (b)Means6 SEMofn=6to12standardizedassayswith whole blood from two donors
who did not exhibit type-specific immunity to the GAS strain used in this study. (D2, D3) supplemented with heat-inactivated antibody serum from D1. (c)
Novel model on potential scabies, bacteria and host interactions. **p,0.01, ***p,0.001 by t test (GraphPad Prism). S. pyogenes strain 2967emm1 was isolated
from human skin.
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Mite Complement Inhibitors Promote GAS Growth
www.plosntds.org 7 July 2012 | Volume 6 | Issue 7 | e1563
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    • "The prevalence of rheumatic heart disease in Indigenous communities is amongst the highest in the world [4, 15]. Several recent studies provide molecular evidence of the scabies mite itself promoting streptococcal growth in pyoderma through complement inhibitors [1, 16, 17]. Association of scabies with these long-term health problems makes it an important factor to consider in Indigenous health. "
    [Show abstract] [Hide abstract] ABSTRACT: The scabies mite, Sarcoptes scabiei, is an obligate parasite of the skin that infects humans and other animal species, causing scabies, a contagious disease characterized by extreme itching. Scabies infections are a major health problem, particularly in remote Indigenous communities in Australia, where co-infection of epidermal scabies lesions by Group A Streptococci or Staphylococcus aureus is thought to be responsible for the high rate of rheumatic heart disease and chronic kidney disease. We collected and separately sequenced mite DNA from several pools of thousands of whole mites from a porcine model of scabies (S. scabiei var. suis) and two human patients (S. scabiei var. hominis) living in different regions of northern Australia. Our sequencing samples the mite and its metagenome, including the mite gut flora and the wound micro-environment. Here, we describe the mitochondrial genome of the scabies mite. We developed a new de novo assembly pipeline based on a bait-and-reassemble strategy, which produced a 14 kilobase mitochondrial genome sequence assembly. We also annotated 35 genes and have compared these to other Acari mites. We identified single nucleotide polymorphisms (SNPs) and used these to infer the presence of six haplogroups in our samples, Remarkably, these fall into two closely-related clades with one clade including both human and pig varieties. This supports earlier findings that only limited genetic differences may separate some human and animal varieties, and raises the possibility of cross-host infections. Finally, we used these mitochondrial haplotypes to show that the genetic diversity of individual infections is typically small with 1-3 distinct haplotypes per infestation.
    Full-text · Article · Feb 2016 · PLoS Neglected Tropical Diseases
  • Source
    • "Scabies cause discomfort to the patient and serious complication as a results of secondary bacterial infection caused by Streptococcus pyogenes (GAS) or Staphylococcus aureus [1]. Recently, a high burden of skin and soft tissue infections (a total of 7252 isolates), and 55% of methicillinresistant S. aureus (MRSA) bloodstream infections were reported and spread out in hospitals across different regions of the world. "
    [Show abstract] [Hide abstract] ABSTRACT: Infectious diseases are a significant cause of morbidity and mortality worldwide, accounting for approximately 50% of all deaths in tropical countries and as much as 20% of deaths in the USA. The emergence of multi-drug resistant (MDR) strains makes the risk of these infections even more threatening and an important public health problem thereby increasing need of new agents for fighting pathogens. In this review, the remarkable antibacterial properties possessed by various snake venoms (Crotalide, Elapidae, and Viperidae families) were discussed and in particular phospholipase A2s (PLA2s) that have emerged from various studies as potential in the last few years. Group IIA PLA2s are the most potent among the snake venom (sv)PLA2s against various types of bacteria. Further, antibacterial derivatives from PLA2s, e.g. peptides derived from the C-terminal sequence of Lys49-PLA2s (amino acids 115-129), kill bacteria and cause severe membrane-damaging effects. Mechanisms of binding to the bacterial surface and subsequent killing by peptides are based on positive charge, hydrophobicity, and length. These peptide candidates are easy to design and synthesize in pure form (~95% purity). Such peptides may be potentially useful in the clinic as new antimicrobials for combating infections due to antibiotic-resistant bacteria that include methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus in the near future.
    Full-text · Article · May 2014 · Mini-Reviews in Organic Chemistry
  • Source
    • "Because scabies mites ingest plasma [16], inactivating host complement may protect the mite gut from complement-mediated damage. Complement inhibition may promote the pyoderma caused by group A streptococci that is often associated with scabies lesions [20]. "
    [Show abstract] [Hide abstract] ABSTRACT: The ectoparasitic mite, Sarcoptes scabiei that burrows in the epidermis of mammalian skin has a long co-evolution with its hosts. Phenotypic studies show that the mites have the ability to modulate cytokine secretion and expression of cell adhesion molecules in cells of the skin and other cells of the innate and adaptive immune systems that may assist the mites to survive in the skin. The purpose of this study was to identify genes in keratinocytes and fibroblasts in human skin equivalents (HSEs) that changed expression in response to the burrowing of live scabies mites. Overall, of the more than 25,800 genes measured, 189 genes were up-regulated >2-fold in response to scabies mite burrowing while 152 genes were down-regulated to the same degree. HSEs differentially expressed large numbers of genes that were related to host protective responses including those involved in immune response, defense response, cytokine activity, taxis, response to other organisms, and cell adhesion. Genes for the expression of interleukin-1α (IL-1α) precursor, IL-1β, granulocyte/macrophage-colony stimulating factor (GM-CSF) precursor, and G-CSF precursor were up-regulated 2.8- to 7.4-fold, paralleling cytokine secretion profiles. A large number of genes involved in epithelium development and keratinization were also differentially expressed in response to live scabies mites. Thus, these skin cells are directly responding as expected in an inflammatory response to products of the mites and the disruption of the skin's protective barrier caused by burrowing. This suggests that in vivo the interplay among these skin cells and other cell types, including Langerhans cells, dendritic cells, lymphocytes and endothelial cells, is responsible for depressing the host's protective response allowing these mites to survive in the skin.
    Preview · Article · Aug 2013 · PLoS ONE
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