Prevalence and mechanisms of cephalosporin resistance in Enterobacteriaceae in London and South-East England.
ABSTRACT To investigate the molecular epidemiology of Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) in London and South-East England.
A prospective study involving 16 hospital microbiology laboratories in London and South-East England was undertaken over a 12 week period. Each laboratory submitted up to 100 consecutive cephalosporin-resistant Enterobacteriaceae isolates judged clinically significant by microbiology staff. Centralized testing was undertaken to confirm organism identification and cephalosporin resistance and to analyse resistance mechanisms.
The predominant mechanism of cephalosporin resistance in isolates from both hospital and community settings was the production of CTX-M-type ESBLs, with CTX-M-producing Escherichia coli as the most numerous resistant organism overall. Other major mechanisms of cephalosporin resistance included production of non-CTX-M ESBLs and AmpC beta-lactamases. Most ESBL (both CTX-M and non-CTX-M) producers were multiply resistant to non-beta-lactam antibiotics, including trimethoprim, ciprofloxacin and gentamicin.
CTX-M enzymes, which were unrecorded in the UK prior to 2000, have become the major mechanism of cephalosporin resistance in Enterobacteriaceae in South-East England. E. coli has overtaken Klebsiella and Enterobacter spp. to become the major host for ESBLs. Due to the multiple antibiotic resistance exhibited by many ESBL-producers, these changes have major implications for antimicrobial therapy.
- SourceAvailable from: Fritz Sörgel[Show abstract] [Hide abstract]
ABSTRACT: The efficacies of tigecycline and ceftazidime against fatal pneumonia in rats caused by an extended-spectrum β-lactamase (ESBL)-positive Klebsiella pneumoniae strain or its wild-type (WT) progenitor were compared. Ceftazidime at 12.5 or 50 mg/kg of body weight twice daily (b.i.d.) was effective (50% or 100% rat survival) in pneumonia caused by the WT isolate but unsuccessful (100% rat mortality) in pneumonia caused by the ESBL-positive variant. In contrast, tigecycline at 6.25, 12.5, or 25 mg/kg b.i.d. showed dosage-dependent efficacy up to 100% rat survival irrespective of the ESBL character of the infecting organism.Antimicrobial Agents and Chemotherapy 01/2013; 57(1). · 4.45 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: To describe the prevalence and risk factors for infection due to AmpC β-lactamase-producing Escherichia coli (AmpC-EC). For the prevalence study, all clinical isolates of E. coli with reduced susceptibility to third-generation cephalosporins were prospectively included from June 2010 to November 2011. For risk factor analysis, a case-control study was conducted. Cases were patients with an infection due to AmpC-EC. Controls were patients infected with cephalosporin-susceptible E. coli, matched 1 : 2. Detection of blaAmpC genes was done with a multiplex AmpC-PCR, and hyperproduction of E. coli chromosomal blaAmpC by quantitative RT-PCR. Alteration of the blaAmpC promoter was studied by PCR and sequencing. We identified 243 (1.1%) AmpC-EC strains out of 21 563 clinical isolates. Three cases with strains carrying ESBLs, 18 strains that were considered due to colonization and 8 cases lost to clinical follow-up were excluded. Finally, 214 cases were included in the analysis. Ninety-one cases (42.5%) and 269 (62.8%) controls were strictly community acquired (P < 0.001). Thirty-five (16.3%) cases and 186 controls (43.5%) did not have any identifiable risk factor (P < 0.001). Among cases, 158 (73.8%) were found to harbour an acquired AmpC (73.4% CMY-2). Previous use of fluoroquinolones [OR 2.6 (95% CI 1.12-3.36); P = 0.008] was independently associated with AmpC-EC in the multivariate analysis. Prevalence of AmpC in E. coli remains low in our area. Plasmid acquisition (CMY type) represents the main mechanism of AmpC production. A high proportion of community-acquired isolates and patients with no identifiable risk factors were found. Previous use of fluoroquinolones was identified as a risk factor. © The Author 2014. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: firstname.lastname@example.org.Journal of Antimicrobial Chemotherapy 12/2014; 70(3). · 5.44 Impact Factor
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ABSTRACT: In order to assess the prevalence and sensitivity pattern of urinary pathogens, 634 midstream urine samples from patients at the Niger Delta University Teaching Hospital, Okolobiri, Nigeria were analysed. Samples were examined microscopically and cultured on blood agar, MacConkey agar and CLED agar. Standard techniques were used for identification of micro-organisms and the Kirby-Bauer disk diffusion method was used for antibiotic testing. Of the 634 urine samples, 237 yielded significant growth meaning a prevalence of 37.38%. There was female preponderance of urinary tract infection. The prevalence increased with age in the female patients peaking in the 21 to 30 years age group. Gram negative bacteria accounted for 82.28% of isolates, with E. coli being the predominant microorganism isolated. The bacterial isolates were most sensitive to nitrofurantoin and most resistant to amoxicillin-clavulanate and cloxacillin. There was a significant proportion of isolates that were resistant to multiple antibiotics, and the resistance levels to most antibiotics was above 50%. There were no differences in resistance pattern between age groups and sex. We recommend periodic assessment of sensitivity patterns of urinary pathogens, rational drug use and institution of infection control measures in the Niger Delta area of Nigeria. We also recommend the use of nitrofurantoin in the treatment of uncomplicated UTI.African journal of microbiology research 01/2012; 6(23):4976-4982. · 0.54 Impact Factor
Journal of Antimicrobial Chemotherapy (2006) 58, 320–326
Advance Access publication 30 May 2006
Prevalence and mechanisms of cephalosporin resistance in
Enterobacteriaceae in London and South-East England
Nicola A. C. Potz1*, Russell Hope2, Marina Warner2, Alan P. Johnson1and David M. Livermore2
on behalf of the London & South East ESBL Project Group
1Healthcare-Associated Infection and Antimicrobial Resistance Department, Health Protection Agency Centre
for Infections, 61 Colindale Avenue, London NW9 5EQ, UK;2Antibiotic Resistance Monitoring and Reference
Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK
Received 20 January 2006; returned 13 March 2006; revised 5 May 2006; accepted 8 May 2006
Objectives: To investigate the molecular epidemiology of Enterobacteriaceae producing extended-
spectrum b-lactamases (ESBLs) in London and South-East England.
Methods: A prospective study involving 16 hospital microbiology laboratories in London and South-East
England was undertaken over a 12 week period. Each laboratory submitted up to 100 consecutive
cephalosporin-resistant Enterobacteriaceae isolates judged clinically significant by microbiology staff.
analyse resistance mechanisms.
Results: The predominant mechanism of cephalosporin resistance in isolates from both hospital and
community settings was the production of CTX-M-type ESBLs, with CTX-M-producing Escherichia coli
as the most numerous resistant organism overall. Other major mechanisms of cephalosporin resistance
included production of non-CTX-M ESBLs and AmpC b-lactamases. Most ESBL (both CTX-M and non-
CTX-M) producers were multiply resistant to non-b-lactam antibiotics, including trimethoprim, ciprofloxa-
cin and gentamicin.
Conclusions: CTX-M enzymes, which were unrecorded in the UK prior to 2000, have become the major
mechanism of cephalosporin resistance in Enterobacteriaceae in South-East England. E. coli has over-
taken Klebsiella and Enterobacter spp. to become the major host for ESBLs. Due to the multiple antibiotic
resistance exhibited by many ESBL-producers, these changes have major implications for antimicrobial
Keywords: ESBLs, CTX-M enzymes, E. coli
Oxyimino-cephalosporins are the ‘workhorse’ antibiotics in many
UK hospitals and are widely used in the therapy of urinary,
respiratory and intra-abdominal infections. Inevitably, this
usage exerts a great selection pressure for resistance which,
among bacteria of the family Enterobacteriaceae, most often
arises via hyperproduction of chromosomal ‘AmpC’ b-lactamases
in Enterobacter spp. and Citrobacter freundii or by the acquisi-
tion of transferable extended-spectrum b-lactamases (ESBLs).1
Until 2003, most ESBL-positive bacteria referred to the Health
Protection Agency’s Centre for Infections were Klebsiella spp.
with mutant forms of the long-known TEM and SHV penicil-
linases. These mutations modify the enzyme’s active site, allow-
ing attack on the cephalosporins, which are stable to the classical
penicillinases. The producers were almost exclusively nosoco-
mial, often from specialist units.2–4
Since 2003, in contrast, multidrug-resistant ESBL-producing
Escherichia coli (especially) and Klebsiella pneumoniae have
been repeatedly confirmed in non-hospitalized patients, both in
the UK and elsewhere in Europe.5,6Many of these have CTX-M
rather than mutant TEM or SHV ESBLs. CTX-M enzymes rep-
resent a distinct class of ESBLs, which arose by gene escape from
a medically unimportant genus, Kluyvera.7Molecular typing
*Corresponding author. Tel: +44-208-327-7217; Fax: +44-208-205-9185; E-mail: nicola.potz@HPA.org.uk
? The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
For Permissions, please e-mail: email@example.com
by guest on June 13, 2013
reveals that some E. coli isolates with CTX-M enzymes belong to
widely disseminated clones, whereas others are diverse.5,8In
either case, most producer isolates are multiresistant not only
to b-lactams but also to quinolones, trimethoprim, tetracyclines
and most aminoglycosides. This complicates therapy, sometimes
necessitating hospitalization of patients for infections that
would otherwise have been managed with oral antibiotics in
The molecular epidemiology, incidence and clinical features
of these organisms have not been adequately studied before in
the UK and were investigated here for London and South-East
Materials and methods
Collection of bacteria
A total of 16 hospital microbiology laboratories participated, 8 in
London and 8 elsewhere in South-East England (see Acknowledge-
ments). These served urban and rural areas and were attached to
hospitals of various sizes. Each laboratory was asked to test all
clinically significant isolates of Enterobacteriaceae against either
cefpodoxime or both cefotaxime and ceftazidime by their routine
method and to submit isolates resistant to any of these agents to
the Antibiotic Resistance Monitoring and Reference Laboratory
(ARMRL). In addition, those laboratories using CLSI (formerly
NCCLS) methods were asked to submit all Enterobacteriaceae giving
zones smaller than the ESBL screening criteria, not only those found
resistant. Laboratories using automated (Vitek or Phoenix) systems
sent isolates indicated by the expert system to have an ESBL and any
found resistant to cefpodoxime, ceftazidime or cefotaxime. Repeat
isolates from the same patient within 30 days were excluded.
Participating laboratories identified isolates using their routine
methods; the provisional identification of ‘coliform’ was considered
acceptable for referred specimens. The study commenced on 1 August
2004 for a 12 week period. A maximum of 100 submissions was
allowed per laboratory. For each isolate submitted, patient demo-
graphic and microbiology laboratory information were collected.
Any isolate submitted without this information was excluded.
Data detailing the number of Enterobacteriaceae isolates tested
in each laboratory during the study period were collected and
sub-divided by specimen type and organism where possible.
Isolates received by ARMRL were identified to the species level
using Chromogenic UTI agar (Oxoid, Basingstoke, UK) to distin-
guish E. coli and using API20E strips (bioMe ´rieux, Marcy l’E´toile,
France) to identify non-E. coli isolates. Antibiotic susceptibility was
assessed by determination of MICs by the British Society for Anti-
microbial Chemotherapy (BSAC) method.9For those agents where
breakpoints are only available for urinary isolates, only urinary isol-
ates were analysed. For agents with differing breakpoints for urinary
and non-urinary isolates, the two groups were analysed separately
using the appropriate breakpoints. Cephalosporins were tested with
and without 4 mg/L clavulanic acid, and isolates where clavulanate
reduced the cephalosporin MIC ‡8-fold were inferred to have
ESBLs, except in the case of those Klebsiella oxytoca isolates
with resistance profiles that otherwise implied hyperproduction of
K1 enzyme.10,11All isolates interpreted as being ESBL-producers
underwent a PCR for blaCTX-M groups.12AmpC-production was
inferred by interpretive reading using identification and MIC
data10and by the detection of plasmid-mediated genes using a
multiplex PCR.13Outer membrane proteins were examined by
SDS–PAGE14for a number of isolates where, based on their anti-
biogram, impermeability was suspected to contribute to resistance.
c2Tests to assess associations between pairs of categorical variables
were calculated using STATA v8.2. Patients with unrecorded age or
sex were excluded from tests for associations with these factors.
Isolates were categorized as either community-associated (those
referred by GPs or from Accident and Emergency Departments)
or hospital-associated (in-patient and out-patient isolates). Specimen
type categories used for analyses were blood, urine and other.
Of 1253 isolates submitted to the ARMRL as cephalosporin
resistant, 1122 (89.5%) were confirmed as resistant by MIC
determination to at least one of cefpodoxime, cefotaxime or
ceftazidime. Of these, 51.2% were E. coli, 21.7% Klebsiella
spp. and 17.9% Enterobacter spp. (Table 1) along with smaller
proportions of Citrobacter, Hafnia, Morganella, Pantoea, Pro-
teus and Serratia spp. The remaining 131 isolates failed to grow,
were contaminated on arrival, were not Enterobacteriaceae or
were not confirmed as resistant to any oxyimino-cephalosporin.
Cephalosporin resistance was attributed to the following
mechanisms, singularly or in combination: (i) production of a
CTX-M-type ESBL, based on positive cephalosporin/clavulanate
synergy tests and a PCR product with universal primers for
blaCTX-M; (ii) production of a non-CTX-M ESBL, based on pos-
itive synergy tests but no PCR product with primers for blaCTX-M;
(iii) production of AmpC b-lactamase, based on resistance to
cefoxitin, cefotaxime and ceftazidime, but not cefepime and
cefpirome, without cephalosporin/clavulanate synergy; and (iv)
other resistance mechanisms. Almost half the isolates confirmed
as cephalosporin resistant (502, 44.7%) produced CTX-M
ESBLs, compared with 149 (13.3%) that had other ESBLs and
190 (16.9%) with high-level AmpC b-lactamase. Two hundred
and eighty-three isolates (25.2%) had mechanisms other than
ESBL or AmpC enzymes. These mostly (n = 273) comprised
isolates with borderline resistance (i.e. MICs one or two dilutions
above the breakpoint) to only one or two cephalosporins
(most often cefpodoxime), but also included 11 K. oxytoca
and Proteus vulgaris inferred to hyperproduce their chromosomal
Of the 574 E. coli, 292 (50.9%) had CTX-M enzymes and 88
(15.3%) had other ESBLs (Table 1); most others (153, 26.7%)
had only borderline cephalosporin resistance but 41 hyperpro-
duced AmpC enzymes, either probably chromosomal (28) or
known acquired types with genes detected in a multiplex PCR
(13). Of 243 cephalosporin-resistant klebsiellae, 199 (81.9%) had
CTX-M enzymes and 27 (11.1%) other ESBLs. Two had an
acquired AmpC enzyme along with a non-CTX-M ESBL and
eight (3.3%) showed only borderline cephalosporin resistance.
Nine (3.7%) were K. oxytoca with a phenotype indicating a
hyperproduced chromosomal K1 b-lactamase. CTX-M enzymes
were much less common in Enterobacter spp. and Citrobacter
spp., accounting for 4.0% (8/201) and 4.1% (2/49) of ceph-
alosporin resistance, respectively, with most cephalosporin res-
istance due to hyperproduced AmpC enzymes (46.3% and 57.1%,
by guest on June 13, 2013
respectively) or non-CTX-M ESBLs (12.9% in Enterobacter spp.
and 6.1% in Citrobacter spp). Two enterobacters had both a
hyperproduced AmpC enzyme and a non-CTX-M ESBL. Border-
line cephalosporin resistance, generally affecting cefpodoxime
but not cefotaxime and ceftazidime, was seen in 74 (36.8%)
Enterobacter spp. and 16 (32.7%) Citrobacter spp.
Prevalence of cephalosporin resistance
Since only cephalosporin-resistant Enterobacteriaceae were col-
lected and different sites used different laboratory and testing
systems the calculation of denominators was complicated. Only
4 of 16 laboratories identified all Enterobacteriaceae isolates to
the species level and these comprised the minority using auto-
mated Phoenix or Vitek systems. Based on these laboratories
alone, it was estimated that 2.5% of all E. coli were cephalosporin
resistant and that 1.1% had CTX-M enzymes (Table 2).
Cephalosporin-resistance rates for Klebsiella and Enterobacter
spp. were 9.7% and 15.7%, respectively, with CTX-M and
other ESBLs present in 7.6% of the Klebsiella spp. and
derepressed AmpC in only 6.7% of Enterobacter spp.
Twelve laboratories provided data on specimen type for all
Enterobacteriaceae isolates (often identified only as ‘coliforms’)
tested during the collection period, but the only two specimen
types consistently categorized by all laboratories were urine and
blood. Of 18685 urinary isolates tested during the study period,
Table 1. Distribution of species and mechanisms of cephalosporin resistance in collected Enterobacteriaceae (n = 1122)
isolates of genusa(95% CI)
total (95% CI)
Citrobacter spp.49 AmpC
CTX-M + OMP losse
other ESBL + AmpC
AmpC + impermeabilityf
CTX-M + OMP loss
other ESBL + impermeability
other ESBL + AmpC
90 Enterobacter spp. 201
Morganella morganii 24
Serratia spp. 24
aWhere total no. of isolates of genus ‡30.
bMechanisms are grouped as follows: (i) CTX-M ESBL, (ii) other ESBL, (iii) AmpC and (iv) other mechanism.
cOther ESBL = non-CTX-M ESBL, predominantly SHM- and TEM-derived.
dOther mechanism = borderline resistance, impermeability, chromosomal b-lactamase.
eOMP, outer membrane protein.
fImpermeability = impermeability profile with unconfirmed OMP loss.
Potz et al.
by guest on June 13, 2013
305 (1.6%) produced CTX-M enzymes, 109 (0.6%) had other
ESBLs and 72 (0.4%) hyperproduced AmpC enzymes. The rate
of cephalosporin resistance was significantly higher (P = 0.001)
amongst the 567 blood isolates tested, at 5.8%; rates for indi-
vidual mechanisms among blood isolates were 3.4% (CTX-M
enzymes), 0.7% (other ESBLs) and 0.7% (hyperproduced
All 16 laboratories participating in the study submitted isolates
of E. coli and K. pneumoniae with CTX-M ESBLs, and the
proportion of CTX-M-producers among all Enterobacteriaceae
tested varied from 0.6% to 4.3% among the 12 laboratories
with known testing denominators (Figure 1); the corresponding
range for non-CTX-M ESBLs was 0.1% to 2.7%. There was
no relationship between prevalence rates for CTX-M and
Multiresistance among cephalosporin-resistant isolates
Most Enterobacteriaceae with CTX-M or non-CTX-M ESBLs
were also resistant to ciprofloxacin, trimethoprim and gentamicin
(Table 3). Nitrofurantoin remained active against many of the
ESBL-producing E. coli but not Klebsiella spp. Mecillinam
appeared active against many ESBL-producers of both genera
but its MICs are prone to inoculum effects and its value against
infections due to ESBL-producers is undetermined.15Enterobac-
teriaceae with a derepressed AmpC were less often resistant to
non-b-lactam antibiotics than were ESBL-producers, probably
because hyperproduction of AmpC is often a consequence of
chromosomal mutation, at least in Enterobacter and Citrobacter
spp., rather than the presence of a multiresistance plasmid.
None of the 1122 isolates with confirmed cephalosporin res-
istance was resistant to the carbapenems imipenem and merope-
nem but a few required ertapenem MICs of ‡4 mg/L. Specifically,
six AmpC-producing Enterobacter spp., one E. coli with an
ESBL and two K. pneumoniae with ESBLs required ertapenem
MICs of 4 to >16 mg/L. Examination revealed that these isolates
had lost outer membrane proteins in the range typical for porins
(31–45 kDa),14implying permeability lesions (not shown).
Descriptive epidemiology of source patients
Among 1116 cephalosporin-resistant isolates for which the sex of
the source patient was available, 36.0% (402) were from males.
This proportion did not significantly change with the mechanism
of resistance (Table 4). The mean patient age was 67.1 years
(range <1–100), with 72.1% of patients aged over 60 years, again
varying insignificantly with the resistance mechanism.
Table 5 shows the distribution of isolates submitted by the
participating laboratories, grouped by hospital- or community-
association. Almost half (49.4%) of the cephalosporin resistance
Table 2. Prevalence of cephalosporin resistance in E. coli, Klebsiella spp. and Enterobacter spp. at four laboratories undertaking full species
identification of all Enterobacteriaceae
Mechanism of cephalosporin resistance
CTX-Mother ESBLhigh-level AmpC other mechanismCephalosporin-susceptible
specimenTotaln % (95% CI)n % (95% CI)n % (95% CI)n % (95% CI)n % (95% CI)
12 0.3 (0.1,0.4)
86.3 (73.7, 94.3)
84.9 (80.7,88.5) 11
aWhere an isolate had more than one mechanism of cephalosporin resistance, each was counted individually. This results in the sum of the individual mechanisms
being greater than the total number of isolates.
CTX-M Non-CTX-MAll ESBLs
ESBL production (%)
Figure 1. Variability among 12 laboratories in prevalence rates of ESBL pro-
duction (%) among Enterobacteriaceae. Individual laboratory prevalence rates
are indicated by filled circles with the mean shown as a short horizontal line.
by guest on June 13, 2013
in hospital-associated isolates was due to CTX-M enzymes.
CTX-M enzymes were also the dominant cephalosporin-
resistance mechanism in community-based isolates, but to a
significantly lesser degree (37.9%, P < 0.001). Prevalence
rates of cephalosporin resistance due to non-CTX-M ESBLs
respectively). If borderline resistance without defined mecha-
nisms was discounted, the proportions of cephalosporin-resistant
isolates with CTX-M enzymes rose to 59.8% and 57.7%
Until at least 2001, ESBLs in the UK were mostly found in
nosocomial Klebsiella spp. and were virtually all TEM and SHV
mutants. However, CTX-M ESBLs were first detected in the UK
in 2000 and their spread has been gathering pace since then, both
in the hospital and community settings.4,5,16This work, the first
prospective study of ESBLs in clinically significant Enterobac-
teriaceae in the UK, confirms their now wide distribution and
dominance among cephalosporin-resistance mechanisms amongst
the Enterobacteriaceae. Over 65% of cephalosporin-resistant
Table 3. Prevalence of resistance among Enterobacteriaceae resistant to one or more of cefotaxime, cefpodoxime and ceftazidime (%)
Percentage resistant (intermediate)
(n = 502; urine n = 395,
non-urine n = 107)
E. coli (n = 292; urine n = 239,
non-urine n = 53)
K. pneumoniae (n = 190;
urine n = 138, non-urine n = 52)
(n = 149; urine n = 120,
non-urine n = 29)
E. coli (n = 89; urine n = 79,
non-urine n = 10)
K. pneumoniae (n = 25;
urine n = 20, non-urine n = 5)
Serratia spp. (n = 144;
urine n = 71, non-urine n = 73)
AmpC-producing E. coli
(n = 41; urine n = 38,
non-urine n = 3)
39.2 89.496.3 (0) 60.2 (1.2) 51.688.6 87.9 (2.8)28.90.0 0.00.4
34.991.696.2 (0) 46.9 (1.4)25.187.483.0 (0)7.50.00.00.3
42.1 91.396.2 (0) 80.0 (1.1) 96.4 90.692.3 (5.8)61.6 0.0 0.00.5
49.067.5 48.3 (0)59.7 (1.4) 37.584.2 55.2 (10.3)49.20.0 0.0 0.7
30.3 74.7NC 57.3 (2.2)13.9 84.8 NC36.7 0.00.0 0.0
60.0 70.0 NC 44.0 (0) 85.075.0 NC 75.00.0 0.00.0
95.8 7.0 16.4 (5.5)15.3 (1.4) 64.836.6 26.0 (15.1)28.2 0.00.04.2
100.0 36.8 NC 22.0 (2.4)21.1 57.9 NC13.20.0 0.0 0.0
aUrinary tract isolates only; the antimicrobial activity against ESBL-producers in this setting is unproven.
bNon-urinary tract isolates only.
Italicized = ESBL-producers should always be reported as cephalosporin resistant.
NC, resistanceratesnotcalculateddueto smallnumberofisolates;FOX,cefoxitin; CIP,ciprofloxacin; GEN,gentamicin;NIT,nitrofurantoin; TMP,trimethoprim;
MEC, mecillinam; IPM, imipenem; MEM, meropenem; ERP, ertapenem.
Table 4. Demographics of patients included in the study
of resistance CTX-M ESBL
Mean age – SD
Age range (years)
% >60 years
67.1 – 22.6
70.5 – 18.8
71.4 – 21.9
66.0 – 24.4
68.8 – 21.1
Potz et al.
by guest on June 13, 2013
E. coli harboured ESBLs, and CTX-M ESBLs outnumbered
non-CTX ESBLs by more than 10:3 in this species. These pro-
portions were even higher among Klebsiella spp. at 93% and 7:1,
ESBLs, while historically restricted to hospital-associated isol-
ates, were shown here to now occur in significant numbers among
isolates from the community, defined here as those submitted by
GPs or by A&E departments. The primary source of such isolates
remains uncertain, with both hospital exposure and food being
possible candidates. Recent studies from both the UK8and Spain6
point to growing gut carriage of ESBL-producing Enterobacteri-
aceae outside of hospitals. Carriage by food animals has also
been noted, though it appears uncommon in the UK and has
not been shown to involve the particular CTX-M-producing
E. coli clones that are most prevalent in humans.17
For all mechanisms of cephalosporin resistance, the mean age
of patients was >60 years and most were females. Similar age and
sex distributions for patients with ESBL-producing bacteria have
been seen in case–control studies investigating ESBL production
in E. coli and Klebsiella spp. in non-hospitalized patients,18,19
and a patient age of over 60 years was shown to be an inde-
pendent risk factor for infection by ESBL-producing bacteria.18,19
ESBL-producing Enterobacteriaceae were seen in greater pro-
portions in blood than urine. This may reflect inadequate treat-
ment of those urinary tract infections where an ESBL-producer is
present, leading to an ‘overspill’ bacteraemia. A BSAC study of
blood pathogens in the UK in 2002 reported ESBLs in 3.2% of
E. coli and 5.0% of Klebsiella spp.20By 2004 these figures had
increased to 6.0% and 18.3%, respectively.21Differences in the
rates observed here may be due to the smaller numbers of isolates
collected in the BSAC study or because it covers the whole of the
British Isles, not just South-East England. No comparable UK
data are published on the proportion of urinary Enterobacteri-
aceae isolates harbouring ESBLs, though one abstract relating to
Leeds22reported 258/2246 urinary isolates (11.5%) resistant to
cefpodoxime, with 83 (3.7%) having ESBLs. There has also been
an increase in ciprofloxacin resistance in recent years in E. coli,
Klebsiella and Enterobacter spp., with a dramatic increase in
E. coli in particular since 2000 from just over 4% in that year
to almost 16% in 2004.23,24
E. coli has also proved to be a surprisingly frequent host for
AmpC-mediated resistance, accounting for over a fifth of the
isolates with high-level AmpC activity in this study. At least
one-third of these isolates had plasmid-coded AmpC genes of
types originating from C. freundii (data not shown),13but the
majority apparently had non-plasmidic AmpC activity probably
arising via overproduction of chromosomal enzymes. Predictably,
AmpC hyperproduction was commonest in Enterobacter spp.,
where it arises readily by a simple high frequency mutation.1
Multiresistance was common among the organisms with
ESBLs, regardless of species and enzyme type. This association
is well recognized and is partly because ESBLs are mostly
encoded by multiresistance plasmids. Treatment with any of sev-
eral antibiotics might therefore select for organisms with ESBLs.
Recent studies on infections with ESBL-producers outside of
hospitals identify prior treatment with cephalosporins, quinolones
and penicillins as risk factors, along with recent hospitalization.25
Inadequate initial antimicrobial therapy is strongly associated
with multidrug resistance and is an independent risk factor for
mortality in severe infections due to ESBL-producing E. coli and
Klebsiella spp.26While resistance to multiple antibiotics limits
the therapeutic options for infections with ESBL-producing
organisms, none of the isolates in the present study was resistant
to imipenem or meropenem and very few were resistant to
ertapenem. It is therefore comforting to observe the continuing
efficacy of the carbapenems against these problematic isolates,
though it is disturbing that the changing nature of resistance in
E. coli (especially) will force more front-line use of these agents.
We thankmembers of theSteering Group(G. Duckworth, HCAI &
AMR Dept., HPA, London; G. Fraser, HPA London; E. Haworth,
HPA South-East), Andre Charlett for his advice on statistical ana-
We also express our thanks and appreciation to the following
colleagues at participating laboratories, without whom this study
would not have been possible:
Ashford (Kent) Microbiology Laboratory: M. Baker, G. Calver;
Hillingdon Hospital: P. Kumari; Kingston Hospital: J. Leach, S.
Patel; Milton Keynes General Hospital: D. Bardell; Northwick
London: I. Balakrishnan, A. Ghafur; Royal Hampshire County
Hospital, Winchester: M. Dryden, M. Grover, S. Lowden;
Queen Elizabeth Hospital, Woolwich: M. Millett, G. Vosper;
Table 5. Isolate submission by participating microbiology
Number of isolates submitted
aNHS Trust categories as defined by the Department of Health (http://www.dh.
bSome laboratories collected isolates for the 12 week period, but their delayed
be cephalosporin-resistant Enterobacteriaceae. Collection periods given are for
all isolates confirmed as cephalosporin-resistant Enterobacteriaceae.
by guest on June 13, 2013
St Peter’s Hospital, Chertsey: S. Baillie; St Thomas Hospital,
London: G. French, K. Shannon; Southampton HPA Laboratory:
H. Humphrey; University College Hospital, London: C. Palmer,
N. Shetty; Worthing Hospital: H. Plumb. This study was partly
sponsored by Merck, Sharp & Dohme (US & UK).
N. A. C. P. received funds from Merck, Sharp & Dohme to present
some of these data at the 15th ECCMID, Copenhagen, 2005.
D. M. L. and A. P. J. have received research grants and/or speaking
honoraria from manufacturers of carbapenem agents. D. M. L.
has shares, inter alia, in GlaxoSmithKline and AstraZeneca.
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