Utility of NCCLS guidelines for identifying extended-spectrum beta-lactamases in non-Escherichia coli and Non-Klebsiella spp. of Enterobacteriaceae

Extended-spectrum β-lactamase infections during pregnancy: a growing threat

Extended-spectrum β-lactamases (ESBLs) are rapidly evolving plasmid transferrable enzymes that confer unique patterns of antibiotic resistance on various bacterial species. Such organisms pose special challenges to laboratory identification, as well as antibiotic selection, administration, and follow-up. Although such infections are increasingly common in the obstetric population, issues surrounding ESBLs are not widely recognized by practicing obstetricians, and controversies exist regarding diagnosis and management. This article provides the practitioner with a summary of clinically pertinent information that will assist in the proper care of pregnant patients with ESBL infection.

Genotyping of ESBL Producing Uropathogenic Escherichia coli in West of Iran

Background and Objective. Urinary tract infection (UTI) is one of the most common bacterial infections in the world. Molecular fingerprinting of UTI isolates such as pulsed-Field Gel Electrophoresis using for Clonal distribution and determine of predominant type. The aim of the study was to determine genotyping of ESBL producing UPECs. Material and Methods. 200 UPEC isolates from outpatients with UTI were obtained. Antimicrobial susceptibility and interpretation were performed by disk diffusion. Virulence factors for UPECs were screened by using PCR. UPECs were analyzed by Pulsed-Field Gel Electrophoresis and images analyzed by Phoretix1DPro software. Results. A total of 200 isolates of UPECs, 24.5% (n = 49) of isolates, were positive for ESBL production. Resistance ranged from 0% for amikacin and imipenem to over 93.9% for carbenicillin and ampicillin. Frequencies of haemagglutination, haemolysin, and hydrophobicity were 51%, 18.3%, and 14.28%, respectively. A total of 10 different genotypes were obtained, which include nine common clones and one single clone. Conclusion. We confirmed the prevalence of virulence phenotyping especially Haemagglutination among UPEC strains and that it can also contribute to virulence in these strains. Large diversity in genotypes was observed in the isolates that could be indicative of different sources of infection in community acquired.

Treatment outcomes in patients with third-generation cephalosporin-resistant Enterobacter bacteremia

BACKGROUND

Infections with resistant Enterobacter spp. are increasingly described, yet data on outcomes associated with these infections are limited.

METHODS

A retrospective cohort study was conducted to investigate outcomes of hospitalized patients with third-generation cephalosporin-resistant (CR) Enterobacter bacteremia. Cephalosporin resistance was detected using cefotaxime and cefpodoxime. Patients with Enterobacter spp. bacteremia from January 2006 through February 2008 defined the population. We defined cases as those with CR isolates; controls were patients with bacteremia due to non-CR isolates. Treatment failure was defined as persistence of the presenting signs of infection 72 h after initial culture collection.

RESULTS

Of the 95 Enterobacter cases identified, 31 (33%) were CR. CR cases were significantly associated with treatment failure (odds ratio (OR) 2.81, 95% confidence interval (CI) 1.14-6.94). This association was not seen after adjustment for age, simplified acute physiology score (SAPS II), and inappropriate empiric antibiotic therapy. Inappropriate empiric therapy (adjusted OR 3.86, 95% CI 1.32-11.31) and SAPS II score (adjusted OR 1.09, 95% CI 1.02-1.16) were significantly associated with treatment failure in the multivariate analysis.

CONCLUSIONS

Third-generation cephalosporin-resistant Enterobacter bacteremia is associated with treatment failure due to receipt of inappropriate empiric antibiotic therapy and severity of illness.

Nosocomial infection and characterization of extended-spectrum β-lactamases-producing Enterobacteriaceae in Northeast Brazil

INTRODUCTION: Extended spectrum β-lactamases (ESBLs) are enzymes that degrade β-lactam antibiotics and have been reported to be an important cause of nosocomial infection in worldwide. METHODS: During 2009, 659 enterobacteria strains were isolated from different clinical specimens and tested for ESBL production. The disk approximation test, combined disk method and addition of clavulanic acid were used for phenotypic detection of the ESBL-producing strains and PCR for detection of the blaTEM and blaCTX-M genes. RESULTS: Among the isolates, 125 were ESBL producers. The blaCTX-M and blaTEM genes were detected in 90.4% and 75% of the strains, respectively. Most strains were isolated from urine. Klebsiella pneumoniae was the most prevalent organism. Microorganisms presented high resistance to the antibiotics. CONCLUSIONS: These results support the need for extending ESBL detection methods to different pathogens of the Enterobacteriaceae family because these methods are only currently standardized by the CLSI for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca and Proteus mirabilis. Carbapenems were the antibiotic class of choice for the treatment of infections caused by ESBL-producing Enterobacteriaceae.

Antimicrobial resistance pattern of Gram-negative bacilli isolated from patients at ICUs of Army hospitals in Iran

BACKGROUND AND OBJECTIVES

Patients at intensive-care-unit (ICU) are at risk of acquiring nosocomial infections which contributes to higher rates. Approximately 25% of all hospital infections and 90% of outbreaks occur in ICUs. Multi- resistant gram-negative rods are important pathogens in ICUs, causing high rate of mortality. The purpose of this study was to investigate the antimicrobial resistance patterns among common Gram-negative bacilli isolated from patients with nosocomial infection at Army Hospitals.

MATERIALS AND METHODS

A total of 187 isolates of Gram-negative bacilli were isolated from 904 patients at ICUs of three Army hospitals in Iran during May 2007 to May 2008. All isolates were examined for antimicrobial resistance using disc diffusion method.

RESULTS

The most frequent pathogens were E. coli (32.08%) followed by K. pneumoniae (31%), P. aeruginosa (12.8%) and Acinetobacter spp. (9.1%). High rate of resistance to third generation cephalosporines was observed among isolates of E. coli and K. pneumoniae. Production of extended spectrum beta lactamases (ESBLs) was found in 46.6% of isolates of both organisms, but in 38% of all Gram negative bacteria.

CONCLUSION

The prevalence of ESBL producing strains at three Army Hospitals is considerable (38%). However, resistance to imipenem has emerged in these hospitals. Furthermore, studies are required to clarify the situation with multi-drug resistant organisms including the Gram positive bacteria at Army hospitals.

Enterobactérias produtoras de ESBL em Passo Fundo, estado do Rio Grande do Sul, Brasil

INTRODUÇÃO: O principal mecanismo de resistência emergente entre Enterobacteriaceae é a produção de β-lactamases de espectro estendido, enzimas capazes de hidrolisar cefalosporinas-de-amplo-espectro, que são bastante utilizadas na terapia antimicrobiana de infecções por enterobactérias. Embora a resistência a esses agentes apresente grande variabilidade geográfica, os índices de resistência são elevados em diversos países MÉTODOS: Um estudo observacional, transversal, descritivo e retrospectivo foi desenvolvido para avaliar a frequência de ESBL entre cepas de Enterobacteriaceae obtidas no Hospital São Vicente de Paulo, Brasil RESULTADOS: A produção de ESBL foi observada em 24,8% (nº=208/838) dos isolados avaliados. Isolados de Escherichia coli representaram 46,2% (nº=96/208) do percentual de produtores de ESBL, seguido de espécies de Enterobacter 30,3% (nº=63/208). A sensibilidade desses isolados ao meropenem foi de 91,4% e a piperacilina/tazobactam de 67,4% CONCLUSÕES: Os índices de ESBL encontrados confirmam a preocupação mundial com este mecanismo de resistência.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. As resistance continues to emerge among a wide range of clinically relevant bacteria, the complexity of this communication increases. This updated version provides an overview of the important susceptibility concerns for most commonly isolated bacterial pathogens.

Identification of plasmid-mediated AmpC beta-lactamases in Escherichia coli, Klebsiella spp., and proteus species can potentially improve reporting of cephalosporin susceptibility testing results

The goal of this study was to determine if the interpretations of extended-spectrum and advanced-spectrum cephalosporins (ESCs and ASCs, respectively) for isolates of Enterobacteriaceae would be impacted by the results of aminophenylboronic acid (APBA) testing. Fifty-three isolates of Escherichia coli, 21 Klebsiella species, and 6 Proteus species that were resistant to at least one ESC were tested by disk diffusion with ceftazidime and cefotetan disks with and without APBA. Ceftazidime disks with and without clavulanic acid (CLAV) were also tested to confirm extended-spectrum beta-lactamase (ESBL) carriage. Twenty-nine (36.3%) isolates were only APBA test positive, 27 were only CLAV test positive, 2 were positive with both substrates, and 22 were negative with both substrates. Thirteen (41.9%) of the 31 APBA-test-positive isolates (all E. coli) tested susceptible to cefotaxime, ceftriaxone, or ceftazidime. Since clinical data suggest that AmpC-producing isolates should be reported as resistant to all ESCs, APBA testing can be helpful in identifying such organisms. Screening for AmpC-producing organisms using nonsusceptibility to cefoxitin and amoxicillin-clavulanate was less specific than APBA testing; it identified ESBL as well as AmpC-producing organisms. Only 18 of 31 APBA-positive isolates were positive by PCR for an AmpC beta-lactamase gene. Thus, testing with APBA could improve the accuracy of reporting ESCs, especially for E. coli. However, results of APBA and CLAV testing did not correlate well for isolates containing both AmpC beta-lactamases and ESBLs. Thus, additional data are needed before formal recommendations can be made on changing the reporting of ASC test results.

Extended-spectrum β-lactamases producing Klebsiella pneumoniae isolated in two hospitals in Goiânia/Brazil: detection, prevalence, antimicrobial susceptibility and molecular typing

This study was developed to evaluate the prevalence of extended-spectrum β-lactamases (ESBL) producing Klebsiella pneumoniae in two hospitals (A and B) in Goiânia, GO, Brazil. The antimicrobial susceptibility of the isolates was determined using the MicroScan WalkAway (Dade Behring, USA). Tests to evaluate the genetic correlation between the isolates were also performed. For the ESBL phenotypic test, the Double-disk diffusion (DD) method was used. The strains isolated in Hospital B were submitted to DNA analysis by pulsed-field gel electrophoresis (PFGE). The study showed high prevalence of ESBL-producing K. pneumoniae (25% in hospital A and 66.7% in hospital B), with high rates of antimicrobial resistance. The most active compound was imipenem (100% susceptibility in vitro). The PFGE test showed similiarity in five strains and variability in six strains.The high prevalence of ESBL-producing Klebsiella may be due to individual selection and to dissemination of a common strain.

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.

Prevalence, microbiology, and clinical characteristics of extended-spectrum beta-lactamase-producing Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii in Korea

We examined the prevalence and characteristics of extended-spectrum beta-lactamase (ESBL)-producing clinical isolates among Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii, and evaluated screening criteria, clinical characteristics and outcomes of infections caused by ESBL-producing organisms. Between January and June 2005, a total of 493 nonduplicate consecutive isolates were collected at Asan Medical Center, a 2,300-bed tertiary hospital in Seoul, Republic of Korea. Fifty isolates (10.1%) were positive for phenotypical ESBL-test. The positive rate of phenotypical ESBL-test in Enterobacter spp., S. marcescens, C. freundii, and M. morganii was 12.8%, 12.4%, 4.9%, and 0% respectively. SHV-12 (18 isolates), CTX-M-9 (17 isolates), and TEM-52 (five isolates) were the most prevalent ESBL types. The ESBL in 17 strains could not be identified. As an ESBL screening criterion, the cefepime MIC >or=1 microg/ml had the highest sensitivity (0.84) and specificity (0.87). Half of the ESBL-producing isolates (25/50) were judged as pathogens. Cholangitis (ten cases), and pneumonia (six cases) were the most common infections. The overall mortality was 12.0%.

Prevalence of AmpC and other beta-lactamases in enterobacteria at a large urban university hospital in Brazil

Production of extended-spectrum beta-lactamases (ESBLs) has been reported in virtually all species of Enterobacteriaceae, which greatly complicates the therapy for infections caused by these organisms. However, the frequency of isolates producing AmpC beta-lactamases, especially plasmid-mediated AmpC (pAmpC), is largely unknown. These beta-lactamases confer resistance to extended-spectrum cephalosporins and aztreonam, a multidrug-resistant (MDR) profile. The aim of the present study was to determine the occurrence of ESBL and pAmpC beta-lactamases in a hospital where MDR enterobacterial isolates recently emerged. A total of 123 consecutive enterobacterial isolates obtained from 112 patients at a university hospital in Rio de Janeiro, Brazil, during March to June 2001 were included in the study. ESBL was detected by the addition of clavulanate to cephalosporin containing disks and by double diffusion. AmpC production was evaluated by a modified tridimensional test and a modified Hodge test. The presence of plasmid-mediated ampC beta-lactamase genes was evaluated by multiplex polymerase chain reaction. Sixty-five (53%) of 123 enterobacterial isolates were MDR obtained from 56 patients. ESBL production was detected in 35 isolates; 5 clonal Escherichia coli isolates exhibited high levels of chromosomal AmpC and ESBL production. However, no isolates contained pAmpC genes. Infection or colonization by MDR enterobacteria was not associated with any predominant resistant clones. A large proportion of hospital infections caused by ESBL-producing enterobacteria identified during the study period were due to sporadic infections rather than undetected outbreaks. This observation emphasizes the need to improve our detection methods for ESBL- and AmpC-producing organisms in hospitals where extended-spectrum cephalosporins are in wide use.

The continuing challenge of ESBLs

Since their first description more than 20 years ago, Escherichia coli and Klebsiella pneumoniae possessing extended-spectrum class A beta-lactamases (ESBLs) continue to thwart our best clinical efforts. In the 'early years' the most common beta-lactamases were of the TEM and SHV varieties. Now, CTX-M enzymes are being discovered throughout the world and are becoming the most prevalent beta-lactamases found in clinical isolates. The K. pneumoniae carbapenemases (KPC) (ESBL-type enzymes that confer resistance to extended-spectrum cephalosporins and carbapenems) present the most significant challenge to date. Structural studies of ESBLs indicate that active site expansion and remodeling are responsible for this extended hydrolytic activity. Continuing questions still exist regarding the optimal detection method for ESBLs. Most relevant are the increasing concerns regarding the status of carbapenems as 'best therapy' for ESBL-producing bacteria in light of the emergence of carbapenemases.

Sensitivity and specificity of various beta-lactam antibiotics and phenotypical methods for detection of TEM, SHV and CTX-M extended-spectrum beta-lactamases

The aim of this study was to compare the sensitivity and specificity of six different beta-lactam antibiotics using five phenotypical tests for detection of extended spectrum beta-lactamases (ESBLs) based on synergism of beta-lactam antibiotics and clavulanate. Experiments were performed on a set of 80 Klebsiella pneumoniae strains and 105 Escherichia coli strains with previously characterized ESBLs (SHV, TEM and CTX-M). ESBLs were detected by five different phenotypical methods: MIC (minimum inhibitory concentration) determination of beta-lactam antibiotics with and without clavulanate, double-disk synergy test (DDST), inhibitor-potentiated disk-diffusion test (IPDDT), CLSI-Clinical and Laboratory Standard Institution (former NCCLS) combined-disk-test, and modified MAST-disk-diffusion test (MAST-DD-test). Seven antibiotics were tested as indicators of ESBL production: ceftazidime, cefotaxime, ceftriaxone, aztreonam, ceftibuten, cefpodoxime and cefepime. Ceftazidime and aztreonam were the best indicators for SHV-5, SHV-12 and TEM beta-lactamases whereas cefotaxime and ceftriaxone were the most sensitive in detection of SHV-2 and CTX-M beta-lactamases in DDST, IPDDT and CLSI test. MIC determination of beta-lactam antibiotics with and without clavulanate was the most sensitive method. DDST was the least sensitive test. Double-disk synergy test, which is the most frequently used test for detection of ESBLs in routine laboratories, was the least sensitive independently of the indicator antibiotic. Since MIC determination is a very laborious and time consuming method, we would recommend the NCCLS combined disk test or IPDD test for detection of ESBLs in routine laboratories with 5 mm zone augmentation breakpoint.

Occurrence of a novel SHV-type enzyme (SHV-55) among isolates of Klebsiella pneumoniae from Portuguese origin in a comparison study for extended-spectrum β-lactamase–producing evaluation

Fifty-five isolates of Klebsiella pneumoniae were evaluated for extended-spectrum beta-lactamase (ESBL) detection and confirmation, using MIC testing by agar dilution, broth microdilution, and the ESBL E-Test (AB Biodisk, Solna, Sweden), according to reference laboratory criteria (RLC) and Clinical and Laboratory Standards Institute (CLSI) guidelines. The RLC classify as ESBL producers those strains for which any MIC of cephalosporins is 3-fold lower in the presence of 2 mug/mL of clavulanate. The E-Test was the only to show 100% sensitivity and specificity to detect ESBL-producer strains with either set of guidelines. MIC determination by agar dilution or broth microdilution, using NCCLS guidelines, showed sensitivity of 92.9%. Nucleotide sequencing allowed the identification of a new ESBL (SHV-55). Overall, this gold standard method confirmed the production of 18 ESBL producers, 36 non-ESBL producers, from which 9 were false ESBL producers (suggesting hyperproduction) and 1 presumptive ESBL TEM-derived. New guidelines for ESBL detection and reliable methods of ESBL identification are required.

Prevalence of newer beta-lactamases in gram-negative clinical isolates collected in the United States from 2001 to 2002

Newer beta-lactamases such as extended-spectrum beta-lactamases (ESBLs), transferable AmpC beta-lactamases, and carbapenemases are associated with laboratory testing problems of false susceptibility that can lead to inappropriate therapy for infected patients. Because there appears to be a lack of awareness of these enzymes, a study was conducted during 2001 to 2002 in which 6,421 consecutive, nonduplicate clinical isolates of aerobically growing gram-negative bacilli from patients at 42 intensive care unit (ICU) and 21 non-ICU sites across the United States were tested on-site for antibiotic susceptibility. From these isolates, 746 screen-positive isolates (11.6%) were referred to a research facility and investigated to determine the prevalence of ESBLs in all gram-negative isolates, transferable AmpC beta-lactamases in Klebsiella pneumoniae, and carbapenemases in Enterobacteriaceae. The investigations involved phenotypic tests, isoelectric focusing, beta-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular analyses. ESBLs were detected only in Enterobacteriaceae (4.9% of all Enterobacteriaceae) and were found in species other than those currently recommended for ESBL testing by the CLSI (formerly NCCLS). These isolates occurred at 74% of the ICU sites and 43% of the non-ICU sites. Transferable AmpC beta-lactamases were detected in 3.3% of K. pneumoniae isolates and at 16 of the 63 sites (25%) with no difference between ICU and non-ICU sites. Three sites submitted isolates that produced class A carbapenemases. No class B or D carbapenemases were detected. In conclusion, organisms producing ESBLs and transferable AmpC beta-lactamases were widespread. Clinical laboratories must be able to detect important beta-lactamases to ensure optimal patient care and infection control.

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.

Utility of the VITEK 2 Advanced Expert System for identification of extended-spectrum beta-lactamase production in Enterobacter spp

Forty clinical isolates of Enterobacter spp. were identified as extended-spectrum beta-lactamase (ESBL) producers by disk diffusion. The VITEK 2 Advanced Expert System (AES) identified the ESBL phenotype in only 25 isolates (62.5%), and erroneously reported cephalosporin susceptibility in 11 isolates (28%). Refinements in the AES are required in order to improve ESBL detection in Enterobacter.

Influx of extended-spectrum beta-lactamase-producing enterobacteriaceae into the hospital

BACKGROUND

The prevalence of infections caused by extended-spectrum beta -lactamase (ESBL)-producing Enterobacteriaceae is increasing worldwide. The influx of these bacteria into hospitals has major implications for infection-control and empirical treatment strategies.

METHODS

Isolates from 2 patient cohorts--patients with gram-negative bacteremia within 2 days after admission and patients screened for fecal colonization at admission--were assessed for ESBL production. ESBL phenotype was confirmed according to Clinical and Laboratory Standards Institute guidelines. Predictors of ESBL phenotype were examined by univariate and multivariate analyses.

RESULTS

Of 80 Enterobacteriaceae isolates from blood samples obtained at admission to the hospital, 13.7% produced ESBL. Thirty-eight patients with ESBL-positive isolates and 72 with ESBL-negative isolates were included in a case-control study. Predictors of ESBL production were male sex and nursing home residence (area under receiver operator characteristic curve, 0.7). Of 241 persons screened at admission, 26 (10.8%) had fecal carriage of ESBL-producing Enterobacteriaceae. Predictors of fecal carriage were poor functional status, antibiotic use, chronic renal insufficiency, liver disease, and use of histamine2 blockers (area under receiver operator characteristic curve, 0.8). Four (15.4%) of the 26 individuals with fecal carriage had subsequent bacteremia with ceftazidime-resistant Enterobacteriaceae, compared with 1 (0.5%) noncarrier (odds ratio, 38.9; P<.001). Of 80 ESBL-producing Enterobacteriaceae isolates obtained at admission, 65 were health care associated, and 15 were community acquired. The 15 community-acquired ESBL-producing Enterobacteriaceae belonged to diverse clones. The most prevalent ESBL gene among these isolates was CTX-M-2 (found in 53.3% of the isolates).

CONCLUSIONS

We report high rates of bacteremia and colonization with ESBL-producing Enterobacteriaceae at admission to our institution, which may undermine infection-control measures and complicate the selection of empirical treatment.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Overview of nosocomial infections caused by gram-negative bacilli

We analyzed data from the National Nosocomial Infections Surveillance (NNIS) System from 1986-2003 to determine the epidemiology of gram-negative bacilli in intensive care units (ICUs) for the most frequent types of hospital-acquired infection: pneumonia, surgical site infection (SSI), urinary tract infection (UTI), and bloodstream infection (BSI). We analyzed >410,000 bacterial isolates associated with hospital-acquired infections in ICUs during 1986-2003. In 2003, gram-negative bacilli were associated with 23.8% of BSIs, 65.2% of pneumonia episodes, 33.8% of SSIs, and 71.1% of UTIs. The percentage of BSIs associated with gram-negative bacilli decreased from 33.2% in 1986 to 23.8% in 2003. The percentage of SSIs associated with gram-negative bacilli decreased from 56.5% in 1986 to 33.8% in 2003. The percentages pneumonia episodes and UTIs associated with gram-negative bacilli remained constant during the study period. The proportion of ICU pneumonia episodes associated with Acinetobacter species increased from 4% in 1986 to 7.0% in 2003 (P<.001, by the Cochran-Armitage chi2 test for trend). Significant increases in resistance rates were uniformly seen for selected antimicrobial-pathogen combinations. Gram-negative bacilli are commonly associated with hospital-acquired infections in ICUs. The proportion of Acinetobacter species associated with ICU pneumonia increased from 4% in 1986 to 7.0% in 2003.

High levels of antimicrobial coresistance among extended-spectrum-beta-lactamase-producing Enterobacteriaceae

We compared the susceptibility of 312 extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae isolates with that of 1,216 ESBL nonproducers. Of ESBL producers, 25% were susceptible to gentamicin, 30% to trimethoprim-sulfamethoxazole, 41% to ciprofloxacin, and 60% to piperacillin-tazobactam. ESBL nonproducers were more often susceptible to these agents. ESBL-producing Enterobacteriaceae represent a major source of resistance to various antibiotics.

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%).

Extended-spectrum beta-lactamases among Enterobacter isolates obtained in Tel Aviv, Israel

The extended-spectrum beta-lactamase (ESBL)-producing phenotype is frequent among Enterobacter isolates at the Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. We examined the clonal relatedness and characterized the ESBLs of a collection of these strains. Clonal relatedness was determined by pulsed-field gel electrophoresis. Isoelectric focusing (IEF) and transconjugation experiments were performed. ESBL gene families were screened by colony hybridization and PCR for bla(TEM), bla(SHV), bla(CTX-M), bla(IBC), bla(PER), bla(OXA), bla(VEB), and bla(SFO); and the PCR products were sequenced. The 17 Enterobacter isolates studied comprised 15 distinct genotypes. All isolates showed at least one IEF band (range, one to five bands) whose appearance was suppressed by addition of clavulanate; pIs ranged from 5.4 to > or = 8.2. Colony hybridization identified at least one family of beta-lactamase genes in 11 isolates: 10 harbored bla(TEM) and 9 harbored bla(SHV). PCR screening and sequence analysis of the PCR products for bla(TEM), bla(SHV), and bla(CTX-M) identified TEM-1 in 11 isolates, SHV-12 in 7 isolates, SHV-1 in 1 isolate, a CTX-M-2-like gene in 2 isolates, and CTX-M-26 in 1 isolate. In transconjugation experiments with four isolates harboring bla(TEM-1) and bla(SHV-12), both genes were simultaneously transferred to the recipient strain Escherichia coli HB101. Plasmid mapping, PCR, and Southern analysis with TEM- and SHV-specific probes demonstrated that a single transferred plasmid carried both the TEM-1 and the SHV-12 genes. The widespread presence of ESBLs among Enterobacter isolates in Tel Aviv is likely due not to clonal spread but, rather, to plasmid-mediated transfer, at times simultaneously, of genes encoding several types of enzymes. The dominant ESBL identified was SHV-12.

Occurrence and molecular analysis of extended-spectrum β-lactamase-producing Proteus mirabilis in Hong Kong, 1999–2002

OBJECTIVES

A study was conducted to evaluate the occurrence and characterization of extended-spectrum beta-lactamases (ESBLs) among blood isolates of Proteus mirabilis collected over a 4 year period in Hong Kong.

METHODS

Production of ESBLs among 99 consecutive and non-duplicate isolates was evaluated by the double-disc synergy test. The ESBLs were characterized by isoelectric focusing and PCR sequencing using specific primers. The epidemiological relationship of the isolates was studied by the Dienes test and PFGE.

RESULTS

ESBLs were identified in 13 isolates, from none in 1999-2000 and up to 18.5% (5/27) in 2001 and 25.8% (8/31) in 2002. The ESBL-producing isolates were more resistant to ceftriaxone than to ceftazidime, and were more likely than non-ESBL-producers to have resistance to ciprofloxacin (76.9% versus 14%) and gentamicin (38.5% versus 9.3%). The ESBL content included CTX-M-13 (n=8), CTX-M-14 (n=3), SHV-5 (n=2), TEM-11 (n=1), and an unidentified ESBL with a pI of 7.5. The Dienes test revealed that the genetic background in the 99 isolates was highly heterogeneous, with 54 distinct types among 92 isolates and seven were non-typeable. Among the 13 ESBL-producing isolates, five different backgrounds, including one cluster (Dienes-pulsotype A) with nine isolates, were identified by both Dienes test and PFGE, thus suggesting both clonal and multi-clonal spread of the CTX-M enzymes.

CONCLUSIONS

Our findings indicate the emergence of CTX-M enzymes among P. mirabilis in Hong Kong. More ESBL screening of this species is required to improve their recognition.

In vitro susceptibilities of aerobic and facultative Gram-negative bacilli isolated from patients with intra-abdominal infections worldwide: the 2003 Study for Monitoring Antimicrobial Resistance Trends (SMART)

OBJECTIVES

The SMART (Study for Monitoring Antimicrobial Resistance Trends) surveillance programme was begun in 2002 to monitor antimicrobial resistance trends among aerobic and facultative Gram-negative bacilli (GNB) isolated from intra-abdominal infections worldwide.

METHODS

In 2003, 74 medical centres from 23 countries collected isolates for testing. Antimicrobial susceptibility testing was performed using broth microdilution according to the NCCLS guidelines for MIC testing.

RESULTS

A total of 5658 aerobic and facultative GNB were isolated from intra-abdominal infections. Enterobacteriaceae composed 84% of the total isolates. Among the agents tested, the carbapenems were the most consistently active against the Enterobacteriaceae. E. coli was the most common isolate (46%), and the susceptibility rate to the quinolone (70-90% susceptible), cephalosporin (80-97% susceptible), aminoglycoside (77-100% susceptible) and carbapenem (99-100% susceptible) agents tested varied among geographic regions, with isolates from the Asia/Pacific region generally being the most resistant. Extended-spectrum beta-lactamases (ESBLs) were detected phenotypically in 9% of E. coli, 14% of Klebsiella spp., and 14% of Enterobacter spp. worldwide. ESBL producers generally had a more antibiotic-resistant profile than non-ESBL producers.

CONCLUSIONS

Antimicrobial resistance among GNB isolated from intra-abdominal infections is a problem worldwide, especially in the Asia/Pacific region. The carbapenems ertapenem, meropenem and imipenem are highly active in vitro against Enterobacteriaceae isolated from intra-abdominal sites, including organisms that produce ESBLs.

Evaluation of an accelerated protocol for detection of extended-spectrum beta-lactamase-producing gram-negative bacilli from positive blood cultures

We evaluated a protocol for the accelerated detection of extended-spectrum beta-lactamases (ESBLs) in gram-negative bloodstream pathogens. Two hundred eighty-three blood culture bottles were subjected to direct ESBL testing by inoculating samples directly from blood culture bottles onto agar plates containing cefotaxime and ceftazidime disks, with and without clavulanate. Standard ESBL testing in accordance with the NCCLS guidelines after subculturing on agar plates was performed in parallel. Results of the direct ESBL testing were reported 2.3 days sooner and were comparable to those of the standard NCCLS method with sensitivity, specificity, and positive and negative predictive values of 100, 98, 94, and 100%, respectively.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. The emergence of resistance in nearly all commonly isolated bacterial organisms has highlighted the need for ongoing dialogue between the laboratory and those who use its services.