Prevalence of extended-spectrum beta-lactamase-producing Enterobacter cloacae in the Asia-Pacific region: results from the SENTRY Antimicrobial Surveillance Program, 1998 to 2001

Characterization of the population structure, drug resistance mechanisms and plasmids of the community-associated Enterobacter cloacae complex in China

Objectives

To investigate the population structure, drug resistance mechanisms and plasmids of community-associated Enterobacter cloacae complex (CA-ECC) isolates in China.

Methods

Sixty-two CA-ECC isolates collected from 31 hospitals across China were typed by hsp60 typing and MLST. ESBL and AmpC-overexpression phenotype was determined by double-disc synergy test. Replicon typing and conjugation were performed for plasmid analysis. All ESBL-positive isolates and representative conjugants were subjected to detailed characterization by WGS.

Results

Enterobacter hormaechei and Enterobacter kobei were predominant in our collections. MLST distinguished 46 STs with a polyclonal structure. ST591 was the most prevalent clone detected in northern China. Twenty-two isolates (35.5%) were ESBL positive and half of them were E. kobei. ESBL positivity was related to ESBL production (15/22) and to AmpC overexpression (18/22). Core-genome phylogenetic analysis identified intra- and inter-regional dissemination of ESBL-producing E. kobei clones. ESBL producers were exclusively classified as E. hormaechei and E. kobei, and blaCTX-M-3 was the most prevalent ESBL genotype (10/15) detected in four different environments. In the ESBL-positive population, the ESBL producers encoded more drug resistance genes (8-24 genes) by carrying more plasmids (1-3 plasmids) than the non-ESBL-producing isolates, resulting in an inter-group difference in drug susceptibilities. IncHI-type plasmids were prevalent in the ESBL producers (12/15). All IncHI2-type plasmids (n = 11) carried ESBL genes and shared a similar backbone to p09-036813-1A_261 recovered from Salmonella enterica in Canada.

Conclusions

The species-specific distribution, species-dependent ESBL mechanism and endemic plasmids identified in our study highlight the necessity for tailored surveillance of CA-ECC in the future.

[Outbreak of multidrug-resistant CTX-M-9-producing Enterobacter cloacae complex in an intensive care unit]

INTRODUCTION

Clinical and epidemiological description of an outbreak in an intensive care unit (ICU) caused by a strain of multidrug-resistant Enterobacter cloacae complex carrying a CTX-M-9-type extended-spectrum β-lactamase (ESBL).

METHODS

A retrospective study of the clinical and epidemiological features of the outbreak caused by E.cloacae complex was performed. Identifying and studying the sensitivity of the strains were performed using the semi-automated system BD Phoenix™, and the characterisation of ESBL using PCR and sequencing. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE).

RESULTS

During February 2014, 6 patients (50% women; mean age: 61.5 years; age range: 44-76 years) admitted to the ICU of the Hospital of Pontevedra (CHOP) presented resistant E.cloacae complex isolates to extended-spectrum cephalosporins. Three patients developed infection; one had primary bacteraemia and septic shock, and 2 with ventilator-associated pneumonia. In the remaining three cases E.cloacae complex isolates were considered as colonisation. Phenotypic and genotypic analysis revealed that all isolates had the same PFGE profile and carried the same CTX-M-9 ESBL. The outbreak was controlled by improving universal precautions and contact isolation of patients infected and/or colonized.

CONCLUSION

The clinical and epidemiological features of an outbreak in an ICU caused by E.cloacae complex carrying CTX-M-9 are described.

A rapid and simple method to detect ESBL in Enterobacter cloacae based on MIC of cefepime

INTRODUCTION

The aim of this study was to identify a rapid and simple phenotypic method for extended-spectrum β-lactamase (ESBL) detection in Enterobacter cloacae.

METHODS

A total of 79 consecutive, non-repeated samples of E. cloacae were evaluated. Four phenotypic methods were applied for ESBL detection, results were compared to multiplex polymerase chain reaction (PCR) as the gold standard reference method: 1) ceftazidime and cefotaxime disks with and without clavulanate, both with boronic acid added; 2) disk approximation using cefepime and amoxicillin/clavulanate; 3) ESBL screening by minimum inhibitory concentration (MIC) ≥ 16µg/mL and 4) by MIC ≥ 2µg/mL for cefepime.

RESULTS

Method 4 showed the best combination of sensitivity (100%) and specificity (94%).

CONCLUSIONS

MIC ≥ 2µg/mL for cefepime would be very useful for the phenotypic detection of ESBL in samples of E. cloacae.

Distribution of extended-spectrum β-lactamases, AmpC β-lactamases, and carbapenemases among Enterobacteriaceae isolates causing intra-abdominal infections in the Asia-Pacific region: results of the study for Monitoring Antimicrobial Resistance Trends (SMART)

The increasing trend of β-lactam resistance among Enterobacteriaceae is a worldwide threat. Enterobacteriaceae isolates causing intra-abdominal infections (IAI) from the Study for Monitoring Antimicrobial Resistance Trends (SMART) collected in 2008 and 2009 from the Asia-Pacific region were investigated. Detection of extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, and carbapenemases was performed by multiplex PCR. A total of 699 Enterobacteriaceae isolates with positive genotypic results, included Escherichia coli (n = 443), Klebsiella pneumoniae (n = 187), Enterobacter cloacae (n = 45), Klebsiella oxytoca (n = 9), Citrobacter freundii (n = 5), Proteus mirabilis (n = 3), Enterobacter aerogenes (n = 2), Morganella morganii (n = 2), and one each of Enterobacter asburiae, Proteus vulgaris, and Providencia rettgeri were analyzed. Nearly 20% of these β-lactamase-producing Enterobacteriaceae isolates were from community-associated IAI. CTX-M (588 isolates, including 428 [72.8%] with CTX-M-15) was the most common ESBL, followed by SHV (n = 59) and TEM (n = 4). CMY (n = 110, including 102 [92.7%] with CMY-2) was the most common AmpC β-lactamase, followed by DHA (n = 46) and ACT/MIR (n = 40). NDM (n = 65, including 62 [95.4%] with NDM-1) was the most common carbapenemase, followed by IMP (n = 7) and OXA (n = 7). Isolates from hospital-associated IAI had more complicated β-lactamase combinations than isolates from the community. Carbapenemases were all exclusively detected in Enterobacteriaceae isolates from India, except that IMP β-lactamases were also detected in Philippines and Australia. CTX-M β-lactamases were the predominant ESBLs produced by Enterobacteriaceae causing IAI in the Asia-Pacific region. Emergence of CTX-M-15-, CMY-2-, and NDM-1-producing Enterobacteriaceae isolates is of major concern and highlights the need for further surveillance in this area.

Characterisation and clinical features of Enterobacter cloacae bloodstream infections occurring at a tertiary care university hospital in Switzerland: is cefepime adequate therapy?

Despite many years of clinical experience with cefepime, data regarding the outcome of patients suffering from bloodstream infections (BSIs) due to Enterobacter cloacae (Ecl) are scarce. To address the gap in our knowledge, 57 Ecl responsible for 51 BSIs were analysed implementing phenotypic and molecular methods (microarrays, PCRs for bla and other genes, rep-PCR to analyse clonality). Only two E. cloacae (3.5%) were ESBL-producers, whereas 34 (59.6%) and 18 (31.6%) possessed inducible (Ind-Ecl) or derepressed (Der-Ecl) AmpC enzymes, respectively. All isolates were susceptible to imipenem, meropenem, gentamicin and ciprofloxacin. Der-Ecl were highly resistant to ceftazidime and piperacillin/tazobactam (both MIC₉₀≥256 μg/mL), whereas cefepime retained its activity (MIC₉₀ of 3 μg/mL). rep-PCR indicated that the isolates were sporadic, but Ecl collected from the same patients were indistinguishable. In particular, three BSIs initially due to Ind-Ecl evolved (under ceftriaxone or piperacillin/tazobactam treatment) into Der-Ecl because of mutations or a deletion in ampD or insertion of IS4321 in the promoter. These last two mechanisms have never been described in Ecl. Mortality was higher for BSIs due to Der-Ecl than Ind-Ecl (3.8% vs. 29.4%; P=0.028) and was associated with the Charlson co-morbidity index (P=0.046). Using the following directed treatments, patients with BSI showed a favourable treatment outcome: cefepime (16/18; 88.9%); carbapenems (12/13; 92.3%); ceftriaxone (4/7; 57.1%); piperacillin/tazobactam (5/7; 71.4%); and ciprofloxacin (6/6; 100%). Cefepime represents a safe therapeutic option and an alternative to carbapenems to treat BSIs due to Ecl when the prevalence of ESBL-producers is low.

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.

Characterization of ertapenem-resistant Enterobacter cloacae in a Taiwanese university hospital

The emergence of carbapenem resistance in Enterobacteriaceae has become a great concern. The aim of this study was to characterize ertapenem-resistant Enterobacter cloacae isolates from a Taiwanese university hospital. A total of 355 nonduplicated E. cloacae isolates collected in 2007 were analyzed by antimicrobial susceptibility testing with and without an inhibitor of efflux pumps and AmpC β-lactamase. The phenotype of extended-spectrum β-lactamase (ESBL), profile of outer membrane proteins (OMPs), and clonal relatedness were investigated by the double-disk synergy test, urea/SDS-PAGE, and pulsed-field gel electrophoresis (PFGE), respectively. β-Lactamase genes were examined by PCR and sequencing, and the expression of efflux pump gene acrB was evaluated by reverse transcription-PCR. The contribution of porin deficiency to resistance was investigated by restoring functional porin genes on plasmids. We demonstrated that ertapenem resistance was prevalent (53/355; 14.9%) in E. cloacae. Among the strains, IMP-8, SHV-12, and TEM-1 β-lactamases were identified in 3 (5.7%), 40 (75.5%), and 46 (86.8%) isolates, respectively. PFGE showed clonal diversity among these isolates. Phenotypes of ESBL, AmpC β-lactamase overproduction, an active efflux pump, and change in the expression of OMPs were found in 18 (34%), 11 (20.8%), 51 (96.2%), and 23 (43.4%) of ertapenem-resistant strains, respectively. Ertapenem MICs were restored in strains with OmpC and OmpF expression plasmids. This study suggests that ESBL, AmpC β-lactamase overproduction, and decreased OMP expression combined with an active efflux pump contribute to the ertapenem resistance of E. cloacae. The presence of IMP-8 may also play a partial role in ertapenem resistance in Taiwan.

Characterization and molecular epidemiology of extended spectrum beta-lactamase producing Enterobacter cloacae isolated from a Tunisian hospital

In 2009, out of the 66 nonrepetitive Enterobacter cloacae collected at Charles Nicolle hospital in Tunisia, 44 were extended spectrum β-lactamase (ESBL) producers. The aim of the current study was to detect and characterize the genes encoding the ESBLs including blaTEM, blaSHV, and blaCTX-M groups by polymerase chain reaction and sequencing. Pulsed-field gel electrophoresis (PFGE) analysis was used to determine the genetic relatedness between isolates. All strains were susceptible to carbapenems. They were resistant to fluoroquinolones, gentamicin, tobramycin, and trimethoprim+sulfamethoxazole but variably resistant to netilmicin, amikacin, and tetracyclines. Sequence analysis of the polymerase chain reaction products revealed the presence of blaCTX-M-15 (39 strains), blaSHV-12 (6 strains), and blaSHV-27 (1 strain). The coexistence of two ESBLs was observed in two isolates harboring, respectively, SHV-12+CTX-M-15 and SHV-27+CTX-M-15. PFGE revealed 36 unrelated profiles. Diffusion of E. cloacae producing CTX-M-15 ESBL in our hospital is the consequence of dissemination of identical or related plasmids harboring the CTX-M-15 gene.

High prevalence of extended-spectrum β-lactamases and qnr determinants in Citrobacter species from Japan: dissemination of CTX-M-2

OBJECTIVES

Extended-spectrum β-lactamases (ESBLs) have become a problem among AmpC-producing Enterobacteriaceae and the emergence of concomitant quinolone resistance in β-lactamase-producing isolates poses a global threat. In this study we investigated the prevalence and regional variation of ESBLs in Japanese clinical isolates of Citrobacter spp. and analysed plasmid-mediated quinolone resistance (PMQR) determinants in ESBL-producing Citrobacter spp.

METHODS

A total of 348 clinical isolates of Citrobacter spp. collected throughout Japan were studied. Screening and the boronic acid disc test were performed to detect ESBLs in Citrobacter spp. with chromosomal AmpC β-lactamases. PCR and sequencing were done to identify ESBL and PMQR genes. For ESBL-producing Citrobacter spp., PFGE was performed using the SfiI restriction enzyme.

RESULTS

The number of ESBL-producing isolates confirmed phenotypically was 67 (19.3%). The prevalence of ESBL-producing Citrobacter koseri was significantly higher (32.1%) than that of ESBL-producing Citrobacter freundii (4.6%) (P < 0.01). Moreover, the prevalence of ESBLs was notably higher among C. koseri from southern Japan (60.0%). CTX-M-2 was predominant in C. koseri. Of the ESBL-producing C. koseri analysed, 23.2% possessed PMQR determinants, and there was a significant association between qnrB4 and bla(SHV-12). The 57 ESBL-producing Citrobacter spp. possessing bla(CTX-M), bla(SHV) or bla(TEM) were divided into 18 unique PFGE types.

CONCLUSIONS

This is the first report about the prevalence of PMQR determinants among ESBL-producing Citrobacter spp. from Japan. Our data suggest that ESBLs and PMQR determinants are spreading among C. koseri in Japan.

Bacteremia due to extended-spectrum-beta-lactamase-producing Enterobacter cloacae: role of carbapenem therapy

Enterobacter cloacae is an important nosocomial pathogen. However, few studies specifically dealing with the clinical characteristics and outcome of extended-spectrum beta-lactamase (ESBL)-producing E. cloacae infections have been published. During an 8-year period in a medical center, of 610 E. cloacae bacteremic isolates, 138 (22.6%) with ESBL genes were designated the ESBL group, and 120 (19.6%) cefotaxime-nonsusceptible isolates without the ESBL phenotype and genes were designated the control group. Of the former group of isolates, 133 (96.3%) carried the bla(SHV-12) gene, 3 (2.1%) had bla(CTX-M3), and 2 (1.4%) had both the bla(SHV-12) and bla(CTX-M3) genes. After patients under the age of 18 years were excluded, there were 206 adults with E. cloacae bacteremia, and these consisted of 121 patients in the ESBL group and 85 in the control group. More episodes of hospital-onset and polymicrobial bacteremia, increased severity of illness, more cases of bacteremia onset in intensive care units (ICUs), and longer stays in the hospital and ICU after bacteremia onset were noted in the ESBL group. However, the crude and sepsis-related mortality rates in two groups were similar. Of the ESBL group, the in-hospital sepsis-related mortality rate of patients definitively treated by a carbapenem was lower than that of those treated by noncarbapenem beta-lactams (5/53, or 9.4%, versus 13/44, or 29.5%; P = 0.01) though the difference was not significant in the hierarchical multivariate analysis (P = 0.46). Among 62 patients with follow-up blood cultures within 14 days of bacteremia onset, breakthrough bacteremia was more common in those treated by a noncarbapenem beta-lactam agent than in those treated by a carbapenem (18/31, or 58.0%, versus 3/31, or 9.6%; P < 0.001). Thus, carbapenem therapy for ESBL-producing E. cloacae that cause bacteremia may provide therapeutic benefits.

Cefepime: a reappraisal in an era of increasing antimicrobial resistance

Cefepime is a 'fourth-generation' cephalosporin with an in vitro extended-spectrum of activity against Gram-negative and Gram-positive pathogens. Cefepime is approved for the treatment of moderate-to-severe infections, such as pneumonia, uncomplicated and complicated urinary tract infections, skin and soft-tissue infections, intra-abdominal infections and febrile neutropenia. In this article, we provide a critical review of pharmacodynamics, clinical management, pharmacokinetics, metabolism, pharmacodynamic target analyses, clinical efficacy, safety and tolerability of cefepime after more than a decade of clinical use.

Boronic acid disk tests for identification of extended-spectrum beta-lactamase production in clinical isolates of Enterobacteriaceae producing chromosomal AmpC beta-lactamases

A study using boronic acid (BA) was designed to detect the extended-spectrum beta-lactamases (ESBLs) in Enterobacteriaceae producing chromosomal AmpC beta-lactamases. A total of 197 clinical isolates of Enterobacter spp. (n=100), Serratia marcescens (n=62) and Citrobacter freundii (n=35) were analysed. Genes encoding ESBLs were detected by polymerase chain reaction (PCR) amplification followed by direct sequencing of PCR products. The Clinical and Laboratory Standards Institute confirmatory test detected only 72.1% of the ESBL-producing isolates. When a > or =5mm increase in the zone diameter of either the cefotaxime/clavulanic acid and/or the ceftazidime/clavulanic acid disks tested in combination with BA versus cefotaxime and/or ceftazidime containing BA was considered to be a positive for ESBL, the method detected 60 (98.4%) of the 61 isolates that harboured ESBLs and showed no false-positive results for ESBL-non-producing isolates. In conclusion, the BA disk test is a highly sensitive and specific method for the detection of ESBLs in Enterobacteriaceae producing chromosomal AmpC beta-lactamases.

An epidemic of plasmids? Dissemination of extended-spectrum cephalosporinases among Salmonella and other Enterobacteriaceae

CTX-M- and AmpC-type beta-lactamases comprise the two most rapidly growing populations among the extended-spectrum cephalosporinases. The evolution and dissemination of resistance genes encoding these enzymes occur mostly through the transmission of plasmids. The high prevalence of clinical isolates of Enterobacteriaceae producing the plasmid-mediated extended-spectrum cephalosporinases resembles an epidemic of plasmids, and has generated serious therapeutic problems. This review describes the emergence and worldwide spread of various classes of plasmid-mediated extended-spectrum cephalosporinases in Salmonella and other Enterobacteriaceae, the transfer mechanism of the plasmids, detection methods, and therapeutic choices.

Characterisation and molecular epidemiology of extended-spectrum beta-lactamase-producing Enterobacter cloacae isolated from a district teaching hospital in Taiwan

Enterobacter cloacae (n = 110) isolates from a district hospital in Taiwan were screened for extended-spectrum beta-lactamases (ESBLs). In total, 17 ESBL-producers were identified, based on the combination-disk synergy test using cefotaxime and ceftazidime +/- clavulanic acid. Investigation of ESBL genes in 33 ceftazidime-resistant isolates revealed the SHV-12 gene in the same 17 ESBL-producers. In addition, one isolate also carried the CTX-M-3 gene, and two isolates also carried the CTX-M-9 gene. No major epidemic clone of ESBL-producers was identified by pulsed-field gel electrophoresis. Routine screening for the ESBL phenotype, focusing on ceftazidime-resistant E. cloacae, should be undertaken in this area.

Determinants of carriage of resistant Escherichia coli in the Indonesian population inside and outside hospitals

OBJECTIVES

Antibiotic resistance is a worldwide healthcare problem exacerbated by antibiotic use and transmission of resistant bacteria. Not much is known about resistance in commensal flora and about determinants for resistance in Indonesia. This study analysed recent antibiotic use as well as demographic, socioeconomic, disease-related and healthcare-related determinants of rectal carriage of resistant Escherichia coli in the community and in hospitals in Indonesia.

METHODS

Carriers of susceptible E. coli were compared with carriers of E. coli with resistance to any of the tested antibiotics. Logistic regression analysis was performed to determine which variables were associated with carriage of resistant E. coli. Individuals in the community with varying levels of contact with healthcare institutions and hospitalized patients were analysed as separate populations.

RESULTS AND CONCLUSIONS

Of 3275 individuals (community 2494, hospital 781), 54% carried resistant E. coli. Recent antibiotic use was the most important determinant of resistance in both populations [community: odds ratio (OR) 1.8, 95% confidence interval (95% CI) 1.5-2.3; hospital: OR 2.5, 95% CI 1.6-3.9]. In the community, hospitalization (OR 2.4, 95% CI 2.0-3.0), diarrhoeal symptoms (OR 1.9, 95% CI 1.3-2.7) and age under 16 years (adults: OR 0.4, 95% CI 0.3-0.5) were associated with carriage of resistant E. coli. For hospitalized patients, having no health insurance was associated with less resistance (OR 0.6, 95% CI 0.4-0.9) and differences were observed between hospitals (Semarang: OR 2.2, 95% CI 1.5-3.3) and departments (Paediatrics: OR 4.3, 95% CI 1.7-10.7). Further research is needed to investigate whether transmission is responsible for these differences.

Nosocomial outbreak due to extended-spectrum-beta-lactamase- producing Enterobacter cloacae in a cardiothoracic intensive care unit

Enterobacter cloacae has been associated with several outbreaks, usually involving strains that overproduce chromosomal beta-lactamase or, uncommonly, strains expressing extended-spectrum beta-lactamases (ESBL). Only sporadic cases of ESBL-producing E. cloacae have been identified in our hospital in recent years. We describe the epidemiology and clinical and microbiological characteristics of an outbreak caused by ESBL-producing E. cloacae in a cardiothoracic intensive care unit (CT-ICU). Prospective surveillance of patients with infection or colonization by ESBL-producing E. cloacae among patients admitted to the CT-ICU was performed during the outbreak. Production of ESBL was determined by decreased susceptibility to expanded-spectrum cephalosporins and a positive double-disk test result. Clone relatedness was determined by pulsed-field gel electrophoresis (PFGE). From July to September 2005, seven patients in the CT-ICU with ESBL-producing E. cloacae were identified (four males; median age, 73 years; range, 45 to 76 years); six patients had cardiac surgery. Four patients developed infections; three had primary bacteremia, one had ventilator-associated pneumonia, and one had tracheobronchitis. ESBL-producing E. cloacae showed resistance to quinolones and aminoglycosides. PFGE revealed two patterns. Five isolates belonged to clone A; two carried a single ESBL (pI 8.2 and a positive PCR result for the SHV type), and three carried two ESBLs (pIs 8.1 and 8.2 and positive PCR results for the SHV and CTX-M-9 types). Isolates belonging to clone B carried a single ESBL (pI 5.4 and a positive PCR result for the TEM type). Review of antibiotic consumption showed increased use of cefepime and quinolones during June and July 2005. The outbreak was stopped by the implementation of barrier measures and cephalosporin restriction. ESBL production could be increasingly common in nosocomial pathogens other than Escherichia coli or Klebsiella pneumoniae.

Prevalence and significance of a negative extended-spectrum beta-lactamase (ESBL) confirmation test result after a positive ESBL screening test result for isolates of Escherichia coli and Klebsiella pneumoniae: results from the SENTRY Asia-Pacific Surveillance Program

A negative extended-spectrum beta-lactamase (ESBL) confirmation test result obtained after a positive ESBL screening test result using Clinical and Laboratory Standards Institute methods has been a common occurrence among isolates of Escherichia coli and Klebsiella pneumoniae in the SENTRY Antimicrobial Surveillance Program in the Asia-Pacific region. Among isolates collected between 1998 and 2004 this screen-positive, nonconfirmed profile (failed to show clavulanate synergy) was observed in 8.9% of 4,515 E. coli isolates and 20.3% of 2,303 K. pneumoniae isolates. We then selected 52 E. coli isolates and 68 K. pneumoniae isolates with a negative ESBL confirmation test, as well as comparable number of isolates with confirmed ESBL-positive tests, and examined them for the presence of TEM, SHV, plasmid-borne ampC, and CTX-M genes. We found that 62% of nonconfirming E. coli isolates and 75% of nonconfirming K. pneumoniae harbored a plasmid-borne AmpC enzyme of the CIT or DHA type. The majority of nonconfirming E. coli and K. pneumoniae from the Asia-Pacific region harbor important beta-lactamases, and a positive screening test alone should be sufficient grounds to report resistance to extended-spectrum cephalosporins in this region.

Susceptibilities of ESBL-Producing Enterobacteriaceae to Ertapenem, Meropenem and Piperacillin-Tazobactam with and without Clavulanic Acid

BACKGROUND

Faced with the extended-spectrum beta-lactamase (ESBL) pandemic, we compared the susceptibilities of ESBL-producing Enterobacteriaceae to ertapenem, meropenem and piperacillin-tazobactam with and without clavulanate.

METHODS

121 strains of Escherichia coli and Klebsiella were studied. 70 strains were originally reported as resistant to ceftazidime based upon disk diffusion; 51 strains were originally reported as sensitive to ceftazidime based upon previous guidelines of the National Committee for Clinical Laboratory Standards, but subsequently shown to be ESBL producers. Minimal inhibitory concentrations (MICs) of the strains towards ertapenem, meropenem and piperacillin-tazobactam were determined by Etest. The effect of adding clavulanate on the MICs was determined by performing the Etest, using plates containing 2 microg/ml of clavulanate.

RESULTS

The MIC90 of all isolates was 0.094 and 0.25 microg/ml for ertapenem, 0.032 and 0.064 microg/ml for meropenem, and 16 and 256 microg/ml for piperacillin-tazobactam with and without clavulanate, respectively.

CONCLUSIONS

ESBL-producing organisms were more susceptible to meropenem than to ertapenem, although the MICs to ertapenem were well within clinically achievable levels. Piperacillin-tazobactam was ineffective in a large percentage of isolates. The presence of clavulanate resulted in a 5-fold decrease in the MIC of ertapenem and in a drastic reduction in the MIC of piperacillin-tazobactam. The decrease observed with ertapenem is unlikely to be of clinical significance. Thus, in our hospital, ertapenem could be a good meropenem-sparing agent for infections due to ESBL-producing organisms. Piperacillin-tazobactam appeared to be a poor choice, as our isolates produce ESBLs which are not successfully inhibited by tazobactam.

Identification of plasmid-mediated extended-spectrum and AmpC β-lactamases in Enterobacter spp. isolated from dogs

The genetic determinants involved in reduced susceptibility to third-generation cephalosporins and aztreonam were identified in ten canine Enterobacter isolates associated with opportunistic infections in three veterinary hospitals in Brisbane, Australia. All isolates were evaluated by a combination of phenotypic (broth microdilution and disc susceptibility, modified disc diffusion and IEF) and genotypic (PFGE, plasmid analysis, Southern blot hybridization, bacterial conjugation, PCR and sequencing) methods to investigate genetic relatedness and to identify plasmid-mediated resistance genes, in particular beta-lactamase genes responsible for extended-spectrum cephalosporin resistance. The ten canine isolates were genotypically diverse based on PFGE and belonged to either Enterobacter cloacae or Enterobacter hormaechei on the basis of 16S rRNA gene sequence analysis. Plasmid profiles were also diverse. Nine isolates contained a transmissible blaSHV-12-carrying plasmid (approximately 140 kb) that also conferred resistance to chloramphenicol, gentamicin, spectinomycin, tetracycline, trimethoprim and sulfonamides. In all plasmid-mediated extended-spectrum beta-lactamase (ESBL)-producing isolates including transconjugants, blaSHV-12 was shown to reside in a approximately 6.5 kb plasmid fragment. The remaining isolate that was not an ESBL producer possessed an AmpC beta-lactamase gene (blaCMY-2) on a approximately 93 kb transmissible plasmid. This plasmid did not contain any other antimicrobial resistance genes. Additional plasmid-mediated beta-lactamases identified in some isolates included bla(TEM) and blaOXA-10. This is the first report of canine Enterobacter isolates containing transmissible plasmid-mediated blaSHV-12 and blaCMY-2 resistance genes. Therefore, Enterobacter isolated from opportunistic infections in dogs may be an important reservoir of plasmid-mediated resistance genes, which could potentially be spread to other members of the Enterobacteriaceae.

Urinary tract infection caused by fluoroquinolone- and cephem-resistant Enterobacteriaceae

In 2001, fluoroquinolone-resistant Escherichia coli isolates emerged in Japan in patients with uncomplicated urinary tract infection (UTI), and accounted for ca. 8% of isolates. This is a worldwide occurrence as reported by the ECO.SENS study. The number of fluoroquinolone- and cephem-resistant Enterobacteriaceae isolates from patients with complicated UTI is increasing. Most cephem-resistant isolates of E. coli, Klebsiella pneumoniae and Proteus mirabilis produce extended-spectrum beta-lactamases (ESBLs). The rates of ESBL-producing Enterobacteriaceae differ between countries but there are ESBL producers in urinary Enterobacteriaceae isolates in most countries. More seriously, most nosocomial ESBL producers are also resistant to non-beta-lactams, such as the fluoroquinolones, fosfomycin and co-trimoxazole. This causes serious problems in the chemotherapy of cystitis.

Prevalence of extended-spectrum β-lactamases in isolates of the Enterobacter cloacae complex from German hospitals

In 2002, 119 isolates of the Enterobacter cloacae complex were collected randomly from 11 German laboratories nationwide. Antibiotic susceptibilities were tested by disk-diffusion tests according to CLSI guidelines, and MICs were determined using Etests. PCRs were performed to amplify all TEM and SHV, and most CTX-M and OXA beta-lactamase genes. PCR products were sequenced to identify the precise extended spectrum beta-lactamase (ESBL) types. Isoelectric focusing (IEF) and PM/PML Etests were used to confirm production of the respective ESBLs. According to susceptibility tests and CLSI criteria, 49 (40%) isolates were resistant to extended-spectrum cephalosporins. Seven (5.8%) isolates were positive in at least one of the PCR assays. Sequencing identified production of TEM-1 beta-lactamase genes by three (2.9%) isolates, and ESBL genes of the CTX-M and SHV beta-lactamase families by five (4.2%) isolates. IEF confirmed the production of beta-lactamases in the expected pI ranges of the respective ESBLs, and four of the five ESBL-producers were detected using the PM/PML Etest. All ESBL-producing isolates showed co-resistance to sulphonamides.

Treatment of infections with ESBL-producing organisms: pharmacokinetic and pharmacodynamic considerations

Susceptibility surveillance investigations have demonstrated an increased incidence of ESBL-producing Gram-negative bacilli. Case cohort studies have suggested clinical relevance associated with ESBL-producing Enterobacteriaciae infection. Yet, current laboratory reporting guidelines classify a large percentage of these organisms in the susceptible category. The regulatory agencies Clinical Laboratory Standards Institute (formly NCCLS) and EUCAST, which oversee these guidelines are in the process of re-evaluating the appropriateness of the current classification system. Pharmacokinetic and pharmacodynamic studies examine the relationship between drug exposure (pharmacokinetics), antibiotic potency (MIC), and treatment efficacy. PK/PD studies and analyses have been useful in demonstrating the relevance of increasingly less susceptible pathogens and specific emerging resistance mechanisms. Recent investigations have examined the impact of ESBL-producing Gram-negative bacilli relative to advanced generation cephalosporin pharmacokinetics. Animal model studies suggest that the pharmacodynamic target associated with efficacy in treatment of ESBL-producing organisms is the same as that in therapy against non-ESBL-producing bacteria (50% T>MIC). Simulation of human pharmacokinetics can predict the likelihood of achieving this PD target with specific cephalosporin dosing regimens. In general, the exposure from usual regimens of the advanced generation cephalosporins would not be anticipated to achieve the PD target for many of the organisms currently classified as susceptible. PK/PD analyses should be useful in re-evaluating current susceptibility breakpoints for ESBL-producing organisms and for optimising drug and regimen choice in treatment of these infections.

SHV-type extended-spectrum beta-lactamase production is associated with Reduced cefepime susceptibility in Enterobacter cloacae

Cefepime is a potentially useful antibiotic for treatment of infections with Enterobacter cloacae. However, in our institution the MIC(90) for E. cloacae bloodstream isolates is 16 microg/ml. PCR amplification of bla genes revealed that one-third (15/45) of E. cloacae bloodstream isolates produced SHV-type extended-spectrum beta-lactamases (ESBLs) in addition to hyperproduction of AmpC-type beta-lactamases. The majority (11/15) of ESBL producers also produced the TEM-1 beta-lactamase. The SHV types included SHV-2, -5, -7, -12, -14, and -30. All but two of the ESBL-producing E. cloacae isolates, but none of the non-ESBL-producing strains, had MICs of cefepime of >or=2 microg/ml. The MIC(90) for cefepime for ESBL-producing strains was 64 mug/ml, while for non-ESBL producers it was 0.5 microg/ml. Using current Clinical and Laboratory Standards Institute breakpoints for cefepime, two thirds (10/15) of ESBL-producing isolates would have been regarded as susceptible to cefepime. Phenotypic ESBL detection methods were generally unreliable with these E. cloacae isolates. Based on these results, pharmacokinetic, pharmacodynamic, and clinical reevaluation of cefepime breakpoints for E. cloacae may be prudent.

Occurrence of extended-spectrum beta-lactamases among chromosomal AmpC-producing Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens in Korea and investigation of screening criteria

We assessed the occurrence and screening criterion for extended-spectrum beta-lactamases (ESBLs) among AmpC-producing Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens. The 413 isolates (158 E. cloacae, 126 C. freundii, and 129 S. marcescens) isolated from 11 clinical laboratories in Korea were investigated. ESBL production was confirmed by double-disk synergy test and inhibitor-potentiated diffusion test using ceftazidime (CAZ), cefotaxime (CTX), aztreonam (AZT), and cefepime (FEP) with or without clavulanic acid. One hundred seven isolates (25.9%) were as ESBL producers. Of them, resistance was transferred by conjugation in 82 isolates. In transconjugants, structural genes for CTX-M (53.7%), TEM (46.3%), SHV (29.3%) were found. To evaluate the ESBL screening minimum inhibitory concentration (MIC) criteria, MICs for cefuroxime, CAZ, CTX, AZT, and FEP were determined and cutoff value was selected using receiver operator characteristic curve. The FEP MIC > or = 1 microg/mL had the highest sensitivity (95.3%), specificity (82.7%), and positive (65.8%) and negative predictive values (98.3%).

In vitro and in vivo activities of novel 6-methylidene penems as beta-lactamase inhibitors

Novel penem molecules with heterocycle substitutions at the 6 position via a methylidene linkage were investigated for their activities and efficacy as beta-lactamase inhibitors. The concentrations of these molecules that resulted in 50% inhibition of enzyme activity were 0.4 to 3.1 nM for the TEM-1 enzyme, 7.8 to 72 nM for Imi-1, 1.5 to 4.8 nM for AmpC, and 14 to 260 nM for a CcrA metalloenzyme. All the inhibitors were more stable than imipenem against hydrolysis by hog and human dehydropeptidases. Piperacillin was combined with a constant 4-microg/ml concentration of each inhibitor for MIC determinations. The combinations reduced piperacillin MICs by 2- to 32-fold for extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae strains. The MICs for piperacillin-resistant (MIC of piperacillin, >64 microg/ml) strains of Enterobacter spp., Citrobacter spp., and Serratia spp. were reduced to the level of susceptibility (MIC of piperacillin, < or =16 microg/ml) when the drug was combined with 4, 2, or 1 microg of these penem inhibitors/ml. Protection against acute lethal bacterial infections with class A and C beta-lactamase- and ESBL-producing organisms in mice was also demonstrated with piperacillin plus inhibitor. Median effective doses were reduced by approximately two- to eightfold compared to those of piperacillin alone when the drug was combined with the various inhibitors at a 4:1 ratio. Pharmacokinetic analysis after intravenous administration of the various inhibitors showed mean residence times of 0.1 to 0.5 h, clearance rates of 15 to 81 ml/min/kg, and volumes of distribution between 0.4 and 2.5 liters/kg. The novel methylidene penem molecules inhibit both class A and class C enzymes and warrant further investigation for potential as therapeutic agents when used in combination with a beta-lactam antibiotic.