Molecular and clinical characterization of plasmid-mediated AmpC β-lactamase-producing Escherichia coli bacteraemia: a comparison with extended-spectrum β-lactamase-producing and non-resistant E. coli bacteraemia

Plasmid-mediated AmpC β-lactamase-producing Escherichia coli (AmpC-E) bacteraemia was characterized by comparison with bacteraemia caused by extended-spectrum β-lactamase (ESBL)-producing E. coli (ESBL-E) and non-resistant E. coli (NR-E) in the era of the worldwide spread of the CTX-M-15-producing O25b-ST131-B2 clone. Of 706 bloodstream E. coli isolates collected between 2005 and 2010 in three Japanese university hospitals, 111 ESBL screening-positive isolates were analysed for AmpC and ESBL genes by PCR. A case–control study was performed in which the cases consisted of all of the patients with AmpC-E bacteraemia. Phylogenetic groups, sequence types and O25b serotype were determined. Twenty-seven AmpC-E isolates (26 of which were of the CMY-2 type) were identified, and 54 ESBL-E and 54 NR-E isolates were selected for the controls. Nineteen AmpC-E isolates were also positive for ESBL. CTX-M-14 was the most prevalent ESBL type among both the AmpC-E and ESBL-E isolates. The O25b-ST131-B2 clone was the most prevalent among the ESBL-E isolates (26%) and the second most prevalent among the NR-E isolates (13%), but only one O25b-ST131-B2 clone was found among the AmpC-E isolates. Twenty-three different sequence types were identified among the AmpC-E isolates. When compared with bacteraemia with ESBL-E, previous isolation of multidrug-resistant bacteria and intravascular catheterization were independently associated with a lower risk for AmpC-E. When compared with NR-E bacteraemia, prior use of antibiotics was the only significant risk factor for AmpC-E. Unlike the spread of the O25b-ST131-B2 clone between ESBL-E and NR-E, the AmpC-E isolates were not dominated by any specific clone.     

Epidemiology of extended-spectrum β-lactamase-producing Escherichia coli in Sweden 2007–2011

Extended-spectrum β-lactamase (ESBL) -producing Enterobacteriaceae have been notifiable according to the Swedish Communicable Disease Act since 2007. A major increase in the number of cases has been observed, with 2099 cases in 2007 and 7225 cases in 2012. The majority of the isolates are Escherichia coli. Additionally, Swedish data on the prevalence of ESBL-producing invasive isolates of E. coli are available through EARS-Net, and through biannual point prevalence studies, where molecular characterization of isolates from the entire country is carried out. This paper describes major trends in the Swedish epidemiology of ESBL-producing E. coli in the period 2007–2012. Isolates from the point prevalence studies were subjected to antimicrobial susceptibility testing, ESBL genotyping, pulsed-field gel electrophoresis, multi-locus sequence typing and phylogenetic grouping with PCR. The distribution of sequence types, resistance genes and susceptibility levels were all stable over the three study periods. The dominating resistance gene conferring ESBL was bla_CTX-M-15, found in 54–58% of the isolates. ST131 represented 34–38% of the isolates. Other major sequence types were ST38, ST69, ST405, ST617 and ST648, each representing 2–6% of the isolates. Phylogenetic group B2 was the most common, and was observed in 41–47% of the isolates. However, among ST131 isolates the B2 phylogenetic group represented 90–98% of the isolates. The most important epidemiological difference seen over time was that the median age of infected women decreased from 62 to 52 years (p <0.0001) and infected men from 67 to 64 years. A potential explanation might be the shift towards a higher proportion of community-acquired infections in individuals lacking comorbidities.     

Activity of doripenem against extended-spectrum β-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates

The in vitro activity of doripenem was evaluated against a recent collection of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates (201 ESBL-producing Enterobacteriaceae [153 Escherichia coli and 48 Klebsiella pneumoniae] and 201 P. aeruginosa). Comparator agents included amikacin, tobramycin, ciprofloxacin, cefepime, cefotaxime, ceftazidime piperacillin-tazobactam, imipenem, and meropenem. Both doripenem and meropenem inhibited 100% of the ESBL-producing Enterobacteriaceae at ≤0.5 μg/mL. For these isolates, the MIC₉₀ of doripenem (0.12 μg/mL) was 4-fold lower than that of imipenem (0.5 μg/mL). Against P. aeruginosa, the MIC₉₀ of doripenem and meropenem was 2 μg/mL, 4-fold lower than that of imipenem (8 μg/mL). At an MIC of ≤2 μg/mL, doripenem, meropenem, and imipenem inhibited 90.5%, 89.6%, and 82.1% of P. aeruginosa isolates, respectively. Doripenem maintained activity against imipenem-nonsusceptible isolates of P. aeruginosa; at an MIC of ≤4 μg/mL, it inhibited 15 of the 25 isolates with MICs for imipenem of >4 μg/mL. Doripenem is active against ESBL-producing Enterobacteriaceae and P. aeruginosa isolates. Its activity is similar to that of meropenem and slightly better than that of imipenem. The results of this study suggest that doripenem could be an alternative therapeutic agent for infections caused by these organisms.     

Epidemiology and risk factors of community onset infections caused by extended-spectrum β-lactamase-producing Escherichia coli strains

Limited clinical information is available regarding community onset infections caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. A case-control study was performed to evaluate the epidemiology and risk factors of these types of infections. A case patient was defined as a person whose clinical sample yielded ESBL-producing E. coli. For each case patient, one control was randomly chosen from a group of outpatients from whom non-ESBL-producing E. coli had been isolated and for whom a clinical sample had been sent to the same laboratory for culturing during the following week. Of 108 cases of ESBL-producing E. coli, 56 (51.9%) were classified as health care associated (HCA). Univariate analysis showed male gender, HCA infection, severe underlying illness, and a prior receipt of antibiotics to be associated with ESBL-producing E. coli. In the multivariate analysis, HCA infection (odds ratio [OR], 3.18; 95% confidence interval [CI], 1.67 to 6.06; P < 0.001) and previous use of antibiotics (OR, 4.88; 95% CI, 2.08 to 11.48; P < 0.001) were found to be significantly associated with the ESBL group. In a multivariate analysis that included each antibiotic, previous use of fluoroquinolone (OR, 7.32; 95% CI, 1.58 to 34.01; P = 0.011) was significantly associated with ESBL-producing E. coli. Of 101 isolates in which ESBLs and their molecular relationships were studied, all isolates produced ESBLs from the CTX-M family (CTX-M-14, 40 isolates; CTX-M-15, 39 isolates; and other members of the CTX-M family, 22 isolates). In conclusion, this study confirms that ESBL-producing E. coli strains are a notable cause of community onset infections in predisposed patients. HCA infection and previous use of fluoroquinolone were significant factors associated with ESBL-producing E. coli in community onset infections.     

Molecular characteristics of extended-spectrum β-lactamase-producing Escherichia coli from Rio de Janeiro,Brazil

Twenty-five extended-spectrum β-lactamase (ESBL)-producing Escherichia coli clinical isolates from Rio de Janeiro, Brazil were characterized by isoelectric focusing, PCR and sequencing of bla^ESBL genes, plasmid-mediated quinolone resistance determinants, phylogenetic groups, replicon typing, pulsed-field electrophoresis, and multilocus sequencing typing. Twenty-three (92%) ESBL-producing E. coli isolates were positive for bla^CTX-M genes, aac(6′)-Ib-cr, and qnrB. Genetic relatedness of ESBL producers clustered seven (28%) CTX-M-15-producing isolates as sequence type (ST)410, clonal complex (CC) 23, and two (8%) as clone O25-ST131. Our results illustrate the predominance of phylogroup A (52%), ST410 (CC 23) and CTX-M-15 among ESBL-producing E. coli isolates from hospitals in Rio de Janeiro.     

Iberian wolf as a reservoir of extended-spectrum β-lactamase-producing Escherichia coli of the TEM, SHV, and CTX-M groups

The intensive use of antibiotics in human and veterinary medicine, associated with mechanisms of bacterial genetic transfer, caused a selective pressure that contributed to the dissemination of antimicrobial resistance in different bacteria groups and throughout different ecosystems. Iberian wolf, due to his predatory and wild nature, may serve as an important indicator of environmental contamination with antimicrobial resistant bacteria. The aim of this study was to characterize the diversity of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates within the fecal microbiota of Iberian wolf. Additionally, the identification of other associated resistance genes, phylogenetic groups, and the detection of virulence determinants were also focused on in this study. From 2008 to 2009, 237 fecal samples from Iberian wolf were collected in Portugal. E. coli isolates with TEM-52, SHV-12, CTX-M-1, and CTX-M-14-type ESBLs were detected in 13 of these samples (5.5%). This study reveals the presence of ESBL-producing E. coli isolates, in a wild ecosystem, which could be disseminated through the environment. Moreover, the presence of resistant genes in integrons and the existence of virulence determinants were shown. The association between antibiotic resistance and virulence determinants should be monitored, as it constitutes a serious public health problem.     

Emergence of extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae during the years 2000 and 2004 in Helsinki,Finland

The molecular epidemiology of 33 Escherichia coli and 81 Klebsiella pneumoniae extended-spectrum β-lactamase-producing health-care-associated and community-acquired isolates collected in the Helsinki district during 2000–2004 was investigated. Clonality studies, antimicrobial susceptibility and genotyping of the isolates were performed. Newly emerging CTX-M-producing E. coli and bla_SHV-12-producing K. pneumoniae isolates were detected. Clonal clusters of both species persisted throughout the study period.     

Shift of CTX-M genotypes has determined the increased prevalence of extended-spectrum β-lactamase-producing Escherichia coli in south-western Sweden

The prevalence of Escherichia coli producing extended-spectrum β-lactamases (ESBLs) markedly increased during 2004–2008 in south-western Sweden, with a greater increase in urinary isolates in hospitals (0.2–2.5%) than in the community (0.2–1.6%). ESBLs of genotype CTX-M predominated, with a significant (p <0.02) shift from the CTX-M-9 to CTX-M-1 phylogroup occurring among urinary ESBL-producing E. coli isolated early (n = 41) as compared with late (n = 221) in the study period. The increase in ESBL-producing E. coli was polyclonal, and only partly attributable to an increase (0–24%) in the number of O25b-ST131 isolates carrying CTX-M-15. The increase was prominent in men and in elderly patients, and warrants continued surveillance.     

Rapid typing of extended-spectrum β-lactamase- and carbapenemase-producing Escherichia coli and Klebsiella pneumoniae isolates by use of SpectraCell RA

Enterobacteriaceae are important pathogens of both nosocomial and community-acquired infections. In particular, strains with broad-spectrum beta-lactamases increasingly cause problems in health care settings. Rapid and reliable typing systems are key tools to identify transmission, so that targeted infection control measures can be taken. In this study, we evaluated the performance of Raman spectroscopic analysis (RA) for the typing of multiresistant Escherichia coli and Klebsiella pneumoniae isolates using the SpectraCell RA bacterial strain analyzer (River Diagnostics). Analysis of 96 unrelated isolates revealed that RA generated highly reproducible spectra and exhibited a discriminatory power that is comparable to pulsed-field gel electrophoresis. Furthermore, adequate results were obtained for three collections of clinical isolates. RA was able to discriminate outbreak-related isolates from isolates that were not involved in an outbreak or transmission. Furthermore, it was found that the RA approach recognized clones, irrespective of the extended-spectrum β-lactamase type. It can be concluded that RA is a suitable typing technique for E. coli and K. pneumoniae isolates. Combining high reproducibility, speed, and ease-of-use, this technique may play an important role in monitoring the epidemiology of these important nosocomial species.     

Molecular characterization of vancomycin-resistant enterococci and extended-spectrum β-lactamase-containing Escherichia coli isolates in wild birds from the Azores Archipelago

To study the prevalence of vancomycin-resistant enterococci (VRE) and extended-spectrum β-lactamase (ESBL)-containing Escherichia coli isolates, and the mechanisms of resistance implicated, 220 faecal samples from wild birds were collected between 2006 and 2010 in the Azores Archipelago. Samples were spread on Slanetz–Bartley agar plates supplemented with 4 mg/l vancomycin and on Levine agar plates supplemented with 2 mg/l cefotaxime for VRE and ESBL-containing E. coli isolation, respectively. vanA-containing enterococcal isolates (four Enterococcus faecium and two Enterococcus durans) and vanC-1 Enterococcus gallinarum isolates were detected in six and seven faecal samples, respectively. VRE isolates showed ampicillin (n=11), ciprofloxacin (n=9), tetracycline (n=6), erythromycin (n=5), quinupristin/dalfopristin (n=3) and high-level kanamycin resistance (n=1). The tet(L) and/or tet(M) gene was found in all tetracycline-resistant isolates and the erm(B) gene in all erythromycin-resistant isolates. Three vanA-containing E. faecium and two E. gallinarum presented specific sequences of the Tn5397 transposon. Four VRE isolates harboured the ace virulence gene. One faecal sample revealed one ESBL-containing E. coli isolate that belongs to the A phylogenetic group, showed a phenotype of resistance to β-lactams and tetracycline, and harboured the bla _CTX-M-14, bla _SHV-12 and the tet(A) genes. To our knowledge, this is the first study to focus on defining the prevalence of VRE and/or ESBL-containing E. coli strains in wild birds from the Azores. The data recovered are essential to improve knowledge about the dissemination of resistant strains through wild ecosystems and their possible implications by transferring these resistances to other animals or to humans.     

Emergence of CTX-M-15 extended-spectrum β-lactamase-producing Klebsiella pneumoniae isolates in Bosnia and Herzegovina

Fifty-seven nosocomial Klebsiella pneumoniae isolates producing extended-spectrum β-lactamases (ESBLs) were collected between February 2007 and November 2007 in different wards of the Sarajevo (Bosnia-Herzegovina) reference hospital. These isolates comprise two major epidemic pulsed-field electrophoresis-defined clones plus two minor clones. In addition to the ESBL-mediated resistance, all strains uniformly showed resistance to ciprofloxacin, gentamicin and tobramycin. The β-lactamases involved in this resistance phenotype were TEM-1, SHV-1, and CTX-M-15, as demonstrated by isoelectric focusing, PCR amplification, and sequencing. TEM-1 and CTX-M-15 β-lactamases, as well as the aminoglycoside resistance determinants, were encoded in plasmids that could be transferred to Escherichia coli by conjugation. In three of the infected patients with the predominant clone, cefoxitin resistance development (MICs >128 mg/L) was documented. The analysis of the outer membrane proteins of the cefoxitin-susceptible and cefoxitin-resistant isolates revealed that the former expressed only one of the two major porins, OmpK36, whereas in the latter, the expression of Ompk36 was altered or abolished. This is the first report of CTX-M-15-producing K. pneumoniae in Bosnia-Herzegovina. Furthermore, we document and characterize for the first time cefoxitin resistance development in CTX-M-15-producing K. pneumoniae.     

Efficacy of pivmecillinam for treatment of lower urinary tract infection caused by extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae

To evaluate the clinical and bacteriological efficacy of pivmecillinam against lower urinary tract infection (UTI) caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae, patients treated for lower UTI with pivmecillinam (n=8) were studied. Patients treated with nitrofurantoin (n=3) and trimethoprim (n=3) or a combination of these agents with pivmecillinam (n=3) were included as a control group. Antimicrobial susceptibility was determined with EUCAST methodology. Bacteriologic cure was defined as <10(3) CFU/ml at follow-up (30 days), and clinical cure as resolved UTI symptoms after completed treatment. All patients receiving pivmecillinam had good clinical response (8/8), but bacteriological cure rates were low (2/8). However, none of the patients with persisting bacteriuria had a relapse of UTI symptoms within 6 months. All isolates were susceptible to the given antimicrobial. Most isolates belonged to the CTX-M-1 group (n=11, 65%) or CTX-M-9-group (n=4, 24%). Four E. coli isolates belonged to the international clone O25b-ST131 (25%). In conclusion, pivmecillinam had good clinical activity against lower UTI caused by ESBL-producing Enterobacteriaceae, but bacteriological cure rates were low. The persistent bacteriuria appears to be of little clinical importance, but larger clinical studies are needed to determine the usefulness of pivmecillinam in infections caused by ESBL-producing bacteria.     

Infections caused by extended-spectrum β-lactamase-producing Enterobacterales after rectal colonization with ESBL-producing Escherichia coli or Klebsiella pneumoniae

ObjectivesInfections as a result of extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E) are considered infections with a high public health burden. In this study, we aimed to identify incidences of and risk factors for healthcare-associated infections (HAIs) after rectal colonization with ESBL-producing Escherichia coli (ESBL-EC) or Klebsiella pneumoniae (ESBL-KP).MethodsThis prospective cohort study was performed in 2014 and 2015. Patients colonized with ESBL-EC or ESBL-KP were monitored for subsequent HAI with ESBL-E and other pathogens. In the case of an ESBL-E infection, rectal and clinical isolates were compared using pulsed-field gel electrophoresis (PFGE), and whole-genome sequencing (WGS) for ESBL-KP isolates. Proportional hazard models were applied to identify risk factors for HAIs, and to analyse competing risks.ResultsAmong all patients admitted to the hospital during the study period, 13.6% were rectally screened for third-generation cephalosporin-resistant Enterobacterales (3GCREB). A total of 2386 rectal carriers of ESBL-EC and 585 of ESBL-KP were included in the study. Incidence density (ID) for HAI with ESBL-E was 2.74 per 1000 patient days at risk (95% confidence interval (CI) 2.16–3.43) among carriers of ESBL-EC, while it was 4.44 per 1000 patient days at risk (95% CI 3.17–6.04) among carriers of ESBL-KP. In contrast, ID for HAI with other pathogens was 4.36 per 1000 patient days at risk (95% CI 3.62–5.21) among carriers of ESBL-EC, and 5.00 per 1000 patient days at risk (95% CI 3.64–6.69) among carriers of ESBL-KP. Cox proportional hazard regression analyses identified colonization with ESBL-KP (HR = 1.58, 95% CI 1.068–2.325) compared with ESBL-EC as independent risk factor for HAI with ESBL-E. The results were consistent over all competing risk analyses.ConclusionsClinicians should be aware of the increased risk of ESBL-E infections among patients colonized with ESBL-KP compared with ESBL-EC that might be caused by underlying diseases, higher pathogenicity of ESBL-KP and other factors.     

Clinical significance of infections caused by extended-spectrum β-lactamase-producing Enterobacteriaceae blood isolates with inducible AmpC β-lactamase

Few studies have investigated the clinical features and outcomes for extended-spectrum β-lactamase (ESBL)-producing Enterobacter spp., Citrobacter spp., Serratia spp., and Morganella morganii (ECSM) bloodstream infections. This study was performed to investigate the clinical features and outcomes for ESBL-producing ECSM bloodstream infections. Patients with ECSM bloodstream infection were enrolled from October 2006 to March 2008. Of 124 patients with ECSM bacteremia, 30 cases (24.2%) were ESBL-producing isolates. Immunosuppressive drugs use within 30 days (p=0.028), indwelling device at the time of bacteremia (p=0.042) and antibiotics use within 3 months (p=0.022) were independently associated with ESBL production in multivariate analysis. Overall 30-day mortality rate was 19.4% (24/124). When the 30-day mortality rate was evaluated, no significant difference was found between the ESBL group (16.6%; 5/30) and non-ESBL group (20.2%; 19/94). Hospitalization was longer in the ESBL group than in the non-ESBL group (65.4±92.8 vs. 32.9±37.8 days, respectively; p=0.007). The recent use of antibiotics (especially broad-spectrum cephalosporins and other β-lactam antibiotics) was an important risk factor for ESBL among ECSM bacteremia. ESBL production of ECSM isolates was not significantly associated with mortality but ESBL-producing organisms have an important impact on the duration of hospital stay and subsequent medical cost.     

Extended-spectrum β-lactamase-producing Escherichia coli bacteremia: Comparison of pediatric and adult populations

Background/Purpose

The prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is increasing worldwide. This study investigated the clinical features and bacteriology of pediatric patients with ESBL-producing E. coli bacteremia and compared their characteristics with those of adult patients.

Impact of changes in CLSI and EUCAST breakpoints for susceptibility in bloodstream infections due to extended-spectrum β-lactamase-producing Escherichia coli

The impact of recent changes in and discrepancies between the breakpoints for cephalosporins and other antimicrobials, as determined by CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST), was analysed in patients with bloodstream infections caused by extended-spectrum β-lactamase (ESBL) producing Escherichia coli in Spain, was analysed. We studied a cohort of 191 episodes of bloodstream infection caused by ESBL-producing E. coli in 13 Spanish hospitals; the susceptibility of isolates to different antimicrobials was investigated by microdilution and interpreted according to recommendations established in 2009 and 2010 by CLSI, and in 2011 by EUCAST. Overall, 58.6% and 14.7% of isolates were susceptible to ceftazidime, and 35.1% and 14.7% to cefepime using the CLSI-2010 and EUCAST-2009/2011 recommendations, respectively (all isolates would have been considered resistant using the previous guidelines). Discrepancies between the CLSI-2010 and the EUCAST-2011 recommendations were statistically significant for other antimicrobials only in the case of amikacin (98.4% versus 75.9% of susceptible isolates; p <0.01). The results varied depending on the ESBL produced. No significant differences were found in the percentage of patients classified as receiving appropriate therapy, following the different recommendations. Four out of 11 patients treated with active cephalosporins according to CLSI-2010 guidelines died (all had severe sepsis or shock); these cases would have been considered resistant according to EUCAST-2011. In conclusion, by using current breakpoints, extended-spectrum cephalosporins would be regarded as active agents for treating a significant proportion of patients with bloodstream infections caused by ESBL-producing E. coli.     

An abbreviated MLVA identifies Escherichia coli ST131 as the major extended-spectrum β-lactamase-producing lineage in the Copenhagen area

Rapid bacterial typing is a valuable and necessary tool in the prevention and detection of outbreaks. The purpose of this study was to adapt a multilocus variable number of tandem repeats analysis (MLVA) for analysis on a benchtop capillary electrophoresis instrument and compare the modified assay with multilocus sequence typing (MLST) for typing cefpodoxime-resistant Escherichia coli (E. coli). Further, we identified the causative resistance mechanisms and epidemiological type of infection for isolates producing extended-spectrum β-lactamases (ESBLs). A collection of E. coli resistant to cefpodoxime was typed by MLST and a modified MLVA assay using a benchtop capillary electrophoresis instrument. Resistance mechanisms were identified by polymerase chain reaction (PCR) and sequencing. Patient history was examined to establish the epidemiological type of infection for ESBL-producing E. coli. MLVA yielded typing results homologous with MLST and it correctly identified E. coli sequence type (ST) 131 that was accounting for 45 % of all ESBL-producing isolates in the sample collection. The majority (76.7 %) of ESBL-producing isolates was healthcare-related and only 23.3 % of the ESBL-producing isolates were community-onset infections (COI), regardless of the ST. Patients with COI were significantly more often of female gender and younger age compared to healthcare-associated infections (HCAI) and hospital-onset infections (HOI). In conclusion, the modified MLVA is a useful tool for the rapid typing of E. coli and it identified ST131 as the predominating ESBL-producing lineage in Copenhagen. Healthcare-related infections were the predominant infection setting of ESBL-producing E. coli and the demographic characteristics differed between patients with COI and healthcare-related infections.     

High prevalence of blaCTX-M extended-spectrum β-lactamase genes in Escherichia coli isolates from pets and emergence of CTX-M-64 in China

As a cause of community-acquired infections, extended-spectrum β-lactamase (ESBL)-producing Escherichia coli constitute an emerging public-health concern. Few data on the molecular epidemiology of ESBL-producing E. coli isolates from pets are available in China. Detection and characterization of ESBL genes (bla_CTX-M, bla_SHV and bla_TEM) was conducted among 240 E. coli isolates recovered from healthy and sick pets in South China from 2007 to 2008. The clonal relatedness of ESBL-producing E. coli isolates was assessed by pulsed field gel electrophoresis. ESBL-encoding genes were identified in 97 (40.4%) of the 240 isolates and 96 (40.0%) of them harbored CTX-M. The most common CTX-M types were CTX-M-14 (n = 45) and CTX-M-55 (n = 24). The recently reported CTX-M-64 was identified in three isolates. Isolates producing CTX-M-27, -15, -65, -24, -3 and -9 were also identified. Ten isolates carried two or three CTX-M types, with the combination of CTX-M-14 and CTX-M-55 being the most frequent (n = 6). ISEcp1 was identified in the upstream region of 93 out of the 107 bla_CTX-M genes (86.9%). The sequence of the spacer region (45 bp) between ISEcp1 and the start codon of all bla_CTX-M-55 genes (except four) was identical to that of bla_CTX-M-64. No major clonal relatedness was observed among these CTX-M producers. It is suggested that the horizontal transfer of bla_CTX-M genes, mediated by mobile elements, contributes to their dissemination among E. coli isolates from pets. Our finding of high prevalence of ESBL in E. coli of companion animal origin illustrates the importance of molecular surveillance in tracking CTX-M-producing E. coli strains in pets.