Extended-spectrum beta-lactamases: the European experience

The Continuing Plague of Extended-Spectrum β-Lactamase Producing Enterbacterales Infections: An Update

Antimicrobial resistance is a common iatrogenic complication of modern life and medical care. One of the most demonstrative examples is the exponential increase in the incidence of extended-spectrum β-lactamases (ESBLs) production among Enterobacteriaceae, that is, the most common human pathogens outside of the hospital setting. Infections resulting from ESBL-producing bacteria are associated with devastating outcomes, now affecting even previously healthy individuals. This poses an enormous burden and threat to public health. This article aims to narrate the evolving epidemiology of ESBL infections and highlights current challenges in terms of management and prevention of these common infections.

Risk factors for carbapenem-resistant Enterobacteriaceae infections: a French case-control-control study

This study aimed to assess characteristics associated with infections due to carbapenem-resistant Enterobacteriaceae (CRE), producing (CPE) or not producing (non-CPE) carbapenemase, among hospitalised patients in 2014-2016 in France. Case-patients with CRE were compared to two control populations. In multivariate analysis comparing 160 CRE cases to 160 controls C1 (patients with a clinical sample positive for carbapenem-susceptible Enterobacteriaceae), five characteristics were linked to CRE: male gender (OR = 1.9; 95% CI = 1.3-3.4), travel in Asia (OR = 10.0; 95% CI = 1.1-91.2) and hospitalisation in (OR = 2.4; 95% CI = 1.3-4.4) or out of (OR = 4.4; 95% CI = 0.8-24.1) France in the preceding 12 months, infection in the preceding 3 months (OR = 3.0; 95% CI = 1.5-5.9), and antibiotic receipt between admission and inclusion (OR = 1.9; 95% CI = 1.0-3.3). In multivariate analysis comparing 148 CRE cases to 148 controls C2 [patients with culture-negative sample(s)], four characteristics were identified: prior infection (OR = 3.3; 95% CI = 1.6-6.8), urine drainage (OR = 3.0; 95% CI = 1.5-6.1) and mechanical ventilation (OR = 3.7; 95% CI = 1.1-13.0) during the current hospitalisation, and antibiotic receipt between admission and inclusion (OR = 6.6; 95% CI = 2.8-15.5). Univariate analyses comparing separately CPE cases to controls (39 CPE vs C1 and 36 CPE vs C2) and non-CPE cases to controls (121 non-CPE vs C1 and 112 non-CPE vs C2), concomitantly with comparison of CPE to non-CPE cases showed that only CPE cases were at risk of previous travel and hospitalisation abroad. This study shows that, among CRE, risk factors are different for CPE and non-CPE infection, and suggests that question patients about their medical history and lifestyle should help for early identification of patients at risk of CPE among patients with CRE.

Complete Sequence of pCY-CTX, a Plasmid Carrying a Phage-Like Region and an ISEcp1-Mediated Tn2 Element from Enterobacter cloacae

A plasmid pCY-CTX carrying a phage-like backbone from an extensively drug-resistant Enterobacter cloacae strain Guangzhou-ECL001 (previously known as CY01) was identified in this study. By Illumina MiSeq 2 × 250-bp paired-end sequencing, de novo assembly, and PCR, full sequence of pCY-CTX was obtained. Plasmid pCY-CTX was a circular plasmid with a length of 116,700 bp, harboring 136 putative open reading frames with the average G + C content of 50.8%. The backbone of pCY-CTX showed high identity to previously reported phage-like plasmid pHCM2 and phage SSU5. In addition, pCY-CTX contained a distinctive ISEcp1-mediated Tn2 region with two resistance genes bla_TEM-1 and bla_CTX-M-3. Transposition unit "ISEcp1- bla_CTX-M-3- orf477" was inserted into the Tn2 structure, dividing Tn2 into two parts. This represents the first identification of a plasmid carrying a phage-like backbone and a distinctive ISEcp1-mediated Tn2 region within bla_TEM-1 and bla_CTX-M-3 in clinical E. cloacae. The finding of phage-like regions located in plasmids provides a new perspective in gene transfer associated with antimicrobial resistance.

The Continuing Plague of Extended-spectrum β-lactamase-producing Enterobacteriaceae Infections

Antimicrobial resistance is a common iatrogenic complication of modern life and medical care. One of the most demonstrative examples is the exponential increase in the incidence of extended-spectrum β-lactamases (ESBLs) production among Enterobacteriaceae, which is the most common human pathogens outside of the hospital settings. Infections resulting from ESBL-producing bacteria are associated with devastating outcomes, now affecting even previously healthy individuals. This development poses an enormous burden and threat to public health. This paper aims to narrate the evolving epidemiology of ESBL infections, and highlight current challenges in terms of management and prevention of these common infections.

Acquisition of Multidrug-Resistant Organisms Among Hospital Patients Hospitalized in Beds Adjacent to Critically Ill Patients

Objective.

To assess whether patients hospitalized in beds physically adjacent to critically ill patients are at increased risk to acquire multidrug-resistant pathogens.

Design.

Cohort study.

Setting.

Shaare Zedek Medical Center, a 550-bed medical referral center.

Patients.

From April to September 2004, we enrolled consecutive newly admitted patients who were hospitalized in beds adjacent to either mechanically ventilated patients or patients designated as “do not resuscitate” (DNR). For each of these patients, we also enrolled a control patient who was not hospitalized in a bed adjacent to a critically ill patient. We collected specimens from the anterior nares, the oral cavity, and the perianal zone at the time of admission and subsequently at 3-day intervals until discharge or death. Specimens were cultured on selective media to detect growth of antibiotic-resistant pathogens, includingAcinetobacter baumannii, methicillin-resistantStaphylococcus aureus(MRSA), extended-spectrum β lactamase (ESBL)–producing Enterobacteriaceae, and vancomycin-resistant enterococci (VRE).

Results.

We enrolled 46 neighbor-control pairs. Among neighbors and controls, respectively, the incidence rates for isolation ofA. baumanniiwas 8.3 and 4 isolations per 100 patient-days (relative risk [RR], 2.1 [95% confidence interval {CI}, 0.8-5.2];P= .12), the incidence rates for MRSA were 1.4 and 2.6 isolations per 100 patient-days (RR, 0.6 [95% CI, 0.1-2.3];P= .45), the incidence rates for ESBL-producing Enterobacteriaceae were 10.5 and 9 isolations per 100 patient-days (RR, 1.2 [95% CI, 0.6-2.4];P= .84), the incidence rates for VRE were 4.3 and 4.8 isolations per 100 patient-days (RR, 0.9 [95% CI, 0.3-2.4];P= 1), and the composite incidence rate was 21.7 and 16.2 isolations per 100 patient-days (RR, 1.3 [95% CI, 0.8-2.3];P= 0.3).

Conclusions.

In this pilot study, we did not detect an increased incidence rate of isolation of multidrug-resistant pathogens among patients hospitalized in beds adjacent to critically ill patients. Further studies with larger samples should be conducted in order to generate valid data and provide patients, physicians, and policy makers with a sufficient knowledge base from which decisions can be made.

Antimicrobial resistance in coagulase-negative staphylococci from Nigerian traditional fermented foods

Background

Coagulase-negative staphylococci have become increasingly recognized as the etiological agent of some infections. A significant characteristic of coagulase-negative staphylococci especially strains isolated from animals and clinical samples is their resistance to routinely used antibiotics although, resistant strains isolated from fermented foods have not been fully reported.

Methods

A total of two hundred and fifty-five CoNS isolates were subjected to antimicrobial susceptibility test using the disc diffusion technique. The minimum inhibitory concentration of the isolates to the tested antibiotics was determined using the microbroth dilution method. Methicillin resistant strains were confirmed by detection of methicillin resistant genes (mecA) and also employing cefoxitin screening test.

Results

The isolates were confirmed to be methicillin resistant by the detection of mecA genes and the cefoxitin screening test. The isolates demonstrated appreciable resistance to ampicillin (86.7%), sulfomethoxazole–trimethoprim (74.9%), amoxicillin–clavulanic acid (52.5%) and oxacillin (35.7%). Methicillin resistance was exhibited by 13 out of the 255 isolates although no mecA gene was detected. It was also observed that the methicillin resistant isolates were prevalent in these traditional foods; iru, kindirmo, nono and wara.

Conclusion

This study has ameliorated the incidence of multiple antibiotic resistant coagulase-negative staphylococci in Nigerian fermented foods and if not tackled adequately might lead to horizontal transfer of antibiotic resistance from food to man.

The complex epidemiology of extended-spectrum β-lactamase-producing Enterobacteriaceae

ABSTRACT 

Antimicrobial resistance is a growing worldwide iatrogenic complication of modern medical care. Extended-spectrum β-lactamases have emerged as one of the most successful resistance mechanisms, limiting our therapeutic options to treat various human infections. The dissemination of these enzymes to the community probably signifies an irreversible step. This paper will review the evolution of human infections associated with extended-spectrum β-lactamase-producing organisms in the past 20 years, and will present and discuss the current challenges, controversies, debates and knowledge gaps in this research field.

Frequency of PER, VEB, SHV, TEM and CTX-M Genes in Resistant Strains of Pseudomonas aeruginosa Producing Extended Spectrum β-Lactamases

Background:

Pseudomonas aeruginosa is the most common pathogen causing nosocomial infections. Resistance of P. aeruginosa strains to broad-spectrum cephalosporins may be mediated by extended-spectrum β-lactamases (ESBLs).

Objectives:

We intended to investigate the prevalence of ESBLs and antimicrobial susceptibilities of P. aeruginosa isolated from patients in Zahedan, Iran.

Materials and Methods:

In this cross-sectional study, during 2012–2013, 116 P. aeruginosa isolates were collected from a teaching hospital in Zahedan, Iran. Susceptibility to eight antimicrobial agents was carried out by disk diffusion method. The ESBL producing strains were detected by combination disk test (CDT). ESBL positive isolates as well as other isolates showing minimum inhibitory concentrations (MICs) ≥ 4 μg/mL for ceftazidime, cefotaxime, ceftriaxone and aztreonam, were screened for the presence of the genes encoding blaTEM, blaSHV, blaPER-1 and blaVEB-1, by polymerase chain reaction (PCR).

Results:

Ciprofloxacin and piperacillin were the most efficient antipseudomonal agents. The results disclosed that 19 (16.37%) of the isolates were multidrug resistant and 8 (6.89%) were ESBL-positive. Of the 116 isolates, 30 (25.86%) were resistant to at least one of the antibiotics ceftazidime, ceftriaxone, cefotaxime or aztreonam and among these 30 (100%), 4 (13.3%), 2 (6.6%) and 2 (6.6%), amplified blaTEM, blaVEB-1, blaPER-1 and blaSHV, respectively. From the 30 TEM-positive isolates, 22 were ESBL-negative. Sequencing of the ESBL genes verified the accuracy of the PCR products.

Conclusions:

According to our results, blaTEM-116 was the most frequent isolated ESBL gene among the P. aeruginosa strains isolated from patients.

Prevalence of extended-spectrum β-lactamase-producing multidrug-resistant Escherichia coli among isolates from community-acquired infections and in silico structural modeling of an ESBL protein

Escherichia coli is a common major cause of bacterial infections in tea tribe patients of the northeast region of Assam, India. In this study, we documented multidrug resistance (MDR) and the prevalence of extended-spectrum β-lactamases (ESBLs) among 148 E. coli strains that were isolated from bacterial infections in tea tribe patients who had a history of self-medication. High prevalence of resistance to ampicillin (82%), amoxicillin (68%), cefixime (60%), norfloxacin (60%), nalidixic acid (60%), and co-trimoxazole (53%) was observed. Of 148 E. coli isolates, 38 (26%) were confirmed as ESBL producers. The ESBL genes were sequenced from highly resistant ESBL producing E. coli isolates. Molecular modeling was performed using MODELLER 9v10 software to determine the three-dimensional structure of a protein. This result indicates that the prevailing reason for the high prevalence of antibiotic resistance in this community is prior exposure to low-quality antibiotics, hence MDR in E. coli is increasing. ESBLs are enzymes that are produced by resistant bacteria that hydrolyze advanced generations of cephalosporin antibiotics and cause resistance, even in patients with community-acquired infections. So our results provide a framework for understanding the structure and possible binding sites of ESBL proteins for drug targeting, and the results were found to be reliable.

Investigation of antibiotic resistance in the genomic era of multidrug-resistant Gram-negative bacilli, especially Enterobacteriaceae, Pseudomonas and Acinetobacter

The increase and spread of multidrug-resistant (MDR) Gram-negative bacteria, including Enterobacteriaceae, Pseudomonas and Acinetobacter species, have become major concerns worldwide. Although the frequent misuse of antibiotic drugs has greatly contributed to worldwide antibiotic resistance by causing a large dispersal of resistance determinants, recent studies demonstrate that these resistance determinants could have emerged from ancient or environmental sources. Moreover, during the last 10 years, we have been witnessing the emergence and development of technologies for high-throughput sequencing, coinciding with an exponential increase in the number of bacterial genomes sequenced. These sequencing technologies allow a complete study of MDR bacterial genomes and are the best way to investigate the genetic determinants of antimicrobial resistance. Accordingly, studies using genome sequencing to decipher resistance determinants in Enterobacteriaceae, Pseudomonas and Acinetobacter species have demonstrated several advantages including, among others: an exhaustive identification of resistance determinants from any clinical, epidemiological or environmental MDR bacterium; identification of the acquisition mechanisms for resistance determinants exchanged between bacterial species through mobile genetic elements and elucidation and understanding, in record time (less than 1 week), of some critical or epidemic events caused by particular pathogenic bacteria. Therefore, it is clear today that the bacterial genome sequencing approach has revolutionized all fields of scientific research and represents a powerful tool to explore the world of microorganisms.

Multiparametric determination of genes and their point mutations for identification of beta-lactamases

More than half of all currently used antibiotics belong to the beta-lactam group, but their clinical effectiveness is severely limited by antibiotic resistance of microorganisms that are the causative agents of infectious diseases. Several mechanisms for the resistance of Enterobacteriaceae have been established, but the main one is the enzymatic hydrolysis of the antibiotic by specific enzymes called beta-lactamases. Beta-lactamases represent a large group of genetically and functionally different enzymes of which extended-spectrum beta-lactamases (ESBLs) pose the greatest threat. Due to the plasmid localization of the encoded genes, the distribution of these enzymes among the pathogens increases every year. Among ESBLs the most widespread and clinically relevant are class A ESBLs of TEM, SHV, and CTX-M types. TEM and SHV type ESBLs are derived from penicillinases TEM-1, TEM-2, and SHV-1 and are characterized by several single amino acid substitutions. The extended spectrum of substrate specificity for CTX-M beta-lactamases is also associated with the emergence of single mutations in the coding genes. The present review describes various molecular-biological methods used to identify determinants of antibiotic resistance. Particular attention is given to the method of hybridization analysis on microarrays, which allows simultaneous multiparametric determination of many genes and point mutations in them. A separate chapter deals with the use of hybridization analysis on microarrays for genotyping of the major clinically significant ESBLs. Specificity of mutation detection by means of hybridization analysis with different detection techniques is compared.

Clinical impact of infections caused by ESBL-producing E. coli and K. pneumoniae

The outcome of infections occurring at different anatomic sites caused by ESBL-producing E. coli or K. pneumoniae was retrospectively analysed for a 3-y period. 23 cases were compared to 46 controls with infections caused by third-generation cephalosporin-susceptible strains matched by age, severity of illness and duration of hospitalization before onset of infection. Only 27.8% of cases received appropriate empirical antimicrobial therapy compared with 79.6% of controls (OR(paired)=0.053, p=0.001). This did not result in higher costs of antibiotic therapy, a longer median post-infection hospital stay or higher mortality in cases of patients with urinary tract or wound infections. In cases of patients with respiratory tract and bloodstream infections (RTI/BSI), median costs of definitive antibiotic treatment were significantly higher than in controls (325 vs 58.9 Euros, p=0.002). Moreover, more case patients with RTI/BSI had a post-infection stay exceeding the 75th percentile of 15 d on ICU and of 18 d in hospital, respectively (50% vs 6.67%, p=0.034). There was no difference in in-hospital mortality between case and control patients with RTI/BSI (25% vs 20%, p=1.0).

Extended-spectrum-beta-lactamase-producing Enterobacteriaceae strains in various types of private health care centers

During a 2004 survey, 49 extended-spectrum-beta-lactamase-producing enterobacteria were collected in 20 French private health care centers and one local hospital. They included 12 CTX-M-producing Escherichia coli strains (1.8% versus 0.3% in a 1999 survey). Most of them belonged to the same clone and contained a bla(CTX-M-15) gene on similar conjugative plasmids.

Nosocomial liver abscess caused by extended-spectrum beta-lactamase-producing Klebsiella pneumoniae

A nosocomial pyogenic liver abscess caused by an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolate presented in a man with adenocarcinoma of the stomach. The K. pneumoniae strain isolated from blood and liver aspirate cultures after antibiotic therapy for recurrent bacteremia was resistant to all extended-spectrum beta-lactams except imipenem and differed from K. pneumoniae strains causing community-acquired liver abscesses.

Detection and genotyping of SHV beta-lactamase variants by mass spectrometry after base-specific cleavage of in vitro-generated RNA transcripts

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) after base-specific cleavage of PCR-amplified and in vitro-transcribed bla(SHV) genes was used for the identification and genotyping of SHV beta-lactamases. For evaluation, bla(SHV) stretches of 21 clinical Enterobacteriaceae isolates were PCR amplified using T7 promoter-tagged forward and reverse primers, respectively. In vitro transcripts were generated with T7 RNA and DNA polymerase in the presence of modified analogues replacing either CTP or UTP. Using RNase A, the in vitro transcripts were base-specifically cleaved at every "T" or "C" position. Resulting cleavage products were analyzed by MALDI-TOF MS, generating a characteristic signal pattern based on the fragment masses. All 21 individual SHV genes were identified unambiguously using reference sequences, and the results were in perfect concordance with those obtained by fluorescent dideoxy sequencing, which represents the current standard method. As multiple point mutations can be detected in a single assay and newly emerged mutations which are not yet described in public databases can be identified too, MALDI-TOF MS appears to be an ideal tool for analysis of sequence polymorphisms in resistance-associated gene loci.

Limiting the emergence of extended-spectrum Beta-lactamase-producing enterobacteriaceae: influence of patient population characteristics on the response to antimicrobial formulary interventions

BACKGROUND

Effective methods to control the emergence of extended-spectrum beta -lactamase-producing Escherichia coli and Klebsiella species (ESBL-EK) remain unclear. Variations in the patient populations at different hospitals may influence the effect of antimicrobial formulary interventions.

METHODS

To examine variations across hospitals in the response to antimicrobial interventions (ie, restriction of ceftazidime and ceftriaxone) designed to curb the spread of ESBL-EK, we conducted a 5-year quasi-experimental study. This study was conducted at 2 hospitals within the same health system: Hospital A is a 625-bed academic medical center, and Hospital B is a 344-bed urban community hospital. All adult patients with a healthcare-acquired clinical culture of ESBL-EK from July 1, 1997 through December 31, 2002 were included.

RESULTS

After the interventions, the use of ceftriaxone decreased by 86% at Hospital A and by 95% at Hospital B, whereas the use of ceftazidime decreased by 95% at Hospital A and by 97% at Hospital B. The prevalence of ESBL-EK at Hospital A decreased by 45% (P < .001), compared with a 22% decrease at Hospital B (P = .36). The following variables were significantly more common among ESBL-EK-infected patients at Hospital B: residence in a long-term care facility (adjusted odds ratio, 3.77 [95% confidence interval, 1.70-8.37]), advanced age (adjusted odds ratio, 1.04 [95% confidence interval, 1.01-1.06]), and presence of a decubitus ulcer (adjusted odds ratio, 4.13 [95% confidence interval, 1.97-8.65]).

CONCLUSIONS

The effect of antimicrobial formulary interventions intended to curb emergence of ESBL-EK may differ substantially across institutions, perhaps as a result of differences in patient populations. Variability in the epidemiological profiles of ESBL-EK isolates at different hospitals must be considered when designing interventions to respond to these pathogens.

Prevalence of derepressed ampC mutants and extended-spectrum beta-lactamase producers among clinical isolates of Citrobacter freundii, Enterobacter spp., and Serratia marcescens in Korea: dissemination of CTX-M-3, TEM-52, and SHV-12

The resistance mechanism of extended-spectrum cephalosporins in clinical isolates of Citrobacter freundii, Enterobacter spp., and Serratia marcescens was studied. Of 152 isolates, 45 isolates (29.6%) were derepressed AmpC mutants and 39 isolates (25.7%) produced extended-spectrum beta-lactamase (ESBLs). The most prevalent ESBLs were CTX-M enzymes, followed by TEM-52 and SHV-12.

Genetic background of Escherichia coli and extended-spectrum beta-lactamase type

ESBL-producing E. coli may arise from interactions between ESBL type, strain genetic background, and selective pressures in various ecologic niches.

To assess the implication of the genetic background of Escherichia coli strains in the emergence of extended-spectrum-β-lactamases (ESBL), 55 TEM-, 52 CTX-M-, and 22 SHV-type ESBL-producing clinical isolates involved in various extraintestinal infections or colonization were studied in terms of phylogenetic group, virulence factor (VF) content (pap, sfa/foc, hly, and aer genes), and fluoroquinolone resistance. A factorial analysis of correspondence showed that SHV type, and to a lesser extent TEM type, were preferentially observed in B2 phylogenetic group strains that exhibited numerous VFs but were fluoroquinolone-susceptible, whereas the newly emerged CTX-M type was associated with the D phylogenetic group strains that lacked VF but were fluoroquinolone-resistant. Thus, the emergence of ESBL-producing E. coli seems to be the result of complex interactions between the type of ESBL, genetic background of the strain, and selective pressures in ecologic niches.

Evaluation of a new screen agar plate for detection and presumptive identification of Enterobacteriaceae producing extended-spectrum β-lactamases

A new agar screen plate for extended-spectrum beta-lactamase (ESBL) detection was evaluated with 50 clinical isolates of ESBL-producing Enterobacteriaceae species: Enterobacter cloacae (n = 10), Escherichia coli (n = 10), Klebsiella oxytoca (n = 3), Klebsiella pneumoniae (n = 25), and Proteus mirabilis (n = 2). Fecal samples were artificially inoculated with 2 concentrations (25 and 250 colony forming units [CFU]/plate) of the test strains and then applied to the new agar screen plates. By this approach, the new agar formula detected growth that was suggestive of ESBL activity in 44 of 50 (88%) and 50 of 50 (100%) of ESBL strains with 25 and 250 CFU/plate, respectively. A limitation of the agar screen plates was a lack of some specificity. Among 15 strains with resistant phenotypes other than ESBL (K1 producers of K. oxytoca, 6 strains; 9 strains with AmpC phenotype), growth was recorded in 7 (25 CFU/plate) and 11 (250 CFU/plate) of 15 strains. In conclusion, the new agar screen plate is a sensitive and convenient method to directly screen for ESBL organisms in rectal swabs or stool samples, with the potential for incorporation into routine clinical laboratory service.

Evaluation of the current National Committee for Clinical Laboratory Standards guidelines for screening and confirming extended-spectrum beta-lactamase production in isolates of Escherichia coli and Klebsiella species from bacteremic patients

The National Committee for Clinical Laboratory Standards (NCCLS) recommendations for screening and confirming the production of extended-spectrum beta-lactamases (ESBLs) were evaluated in 115 isolates of Escherichia coli and 157 isolates of Klebsiella spp. from Israeli patients with bacteremia. All isolates were screened using cefotaxime, ceftazidime, and cefpodoxime discs. Confirmatory tests using pairs of discs containing ceftazidime, cefotaxime, or cefpodoxime in which clavulanic acid was added to one of the discs in each pair [inhibitor-potentiated disc diffusion test (IPDDT)] and two double-sided E test strips containing ceftazidime or cefotaxime with and without clavulanic acid were performed on all isolates regardless of the results of screening tests. Isolates that tested positive by one or more confirmatory tests were considered ESBL producers. Overall, 69 (25.4%) strains were found to be ESBL producers. The sensitivity of the NCCLS screening criteria ranged between 98.6% for cefotaxime and 92.8% for ceftazidime, and the specificity ranged between 100% for cefotaxime and cefpodoxime and 99.0% for ceftazidime. The sensitivity of the confirmatory tests ranged between 97.1% for the cefotaxime E test and only 75.4% for the ceftazidime IPDDT discs. All 64 isolates that fell in the intermediate and resistant categories for cefotaxime, as well as all 41 in the same categories for ceftazidime and 68 of 69 in these categories for cefpodoxime, were confirmed as ESBL producers. The use of multiple antimicrobial discs for screening isolates and combinations of IPPDT discs is needed to improve the sensitivity of confirmatory testing. It is recommended that isolates falling in the intermediate and resistant categories in disc diffusion testing be reported as ESBL producers. The use of confirmatory tests should be limited to organisms with inhibition zone diameters ranging between the NCCLS recommendations for ESBL screening and the intermediate category breakpoints.

Multiple outbreaks of nosocomial salmonellosis in Russia and Belarus caused by a single clone of Salmonella enterica serovar Typhimurium producing an extended-spectrum beta-lactamase

Thirty-four cefotaxime-resistant Salmonella enterica serovar Typhimurium isolates representative of the isolates that caused outbreaks of gastroenteritis in 10 hospitals in seven regions of Russia and Belarus from 1994 to 2003 were analyzed. All isolates produced the CTX-M-5-like extended-spectrum beta-lactamase, which confers high-level resistance to cefotaxime and ceftriaxone and decreased susceptibility to ceftazidime. The bla(CTX-M) genes were located on small (7.4- to 12-kb) non-self-transferable plasmids approximately 20 bp downstream of the ISEcp1 insertion sequences. Some isolates carried additional conjugative plasmids mediating resistance to penicillin-inhibitor combinations and various non-beta-lactam agents, including tetracycline, chloramphenicol, gentamicin, tobramycin, and co-trimoxazole. Despite the minor differences in susceptibility patterns, all isolates were considered clonally related on the basis of arbitrarily primed PCR and pulsed-field gel electrophoresis analysis. The similarities of the restriction profiles of the CTX-M-coding plasmids further supported the clonal origin of these isolates.

In vitro killing of parenteral beta-lactams against standard and high inocula of extended-spectrum beta-lactamase and non-ESBL producing Klebsiella pneumoniae

Minimum inhibitory concentrations and time-kill curves were performed against 8 Klebsiella pneumoniae (4 non-extended-spectrum beta-lactamase[ESBL] and 4 ESBL) for piperacillin/tazobactam (40/5 microg/mL), cefepime (20 microg/mL), and meropenem (4 microg/mL) by using a standard and high inocula. Imipenem was evaluated only at the standard inoculum for the non-ESBL and ESBL isolates. Samples were withdrawn at 7 predetermined time-points over 24 hours and plated on trypticase soy agar plates. Minimum inhibitory concentrations were: piperacillin/tazobactam 4 to 8 microg/mL (ESBL and non-ESBL), cefepime 1 to 2 microg/mL (ESBL) and 0.06 to 0.125 microg/mL (non-ESBL), imipenem 0.125 to 0.25 microg/mL (ESBL and non-ESBL), and meropenem 0.03 to 0.06 microg/mL (ESBL and non-ESBL). Each antibiotic reached and maintained bactericidal killing (> or =3 log killing) for 24 hours against all non-ESBL isolates for both the standard and high inoculum. Cefepime, imipenem, and meropenem showed the same bactericidal activity against each ESBL isolate at the standard inoculum, whereas piperacillin/tazobactam showed bactericidal killing against only 1 ESBL isolate. At the high inoculum, cefepime and piperacillin/tazobactam were unable to maintain bactericidal activity against any of the ESBL isolates. Only meropenem was able to maintain bactericidal killing over 24 hours against the ESBL isolates at the high inoculum. In summary, meropenem and imipenem maintained bactericidal activity against non-ESBL and ESBL K. pneumoniae irrespective of the inoculum size. While piperacillin/tazobactam and cefepime are bactericidal against non-ESBL K. pneumoniae, their activity against ESBL K. pneumoniae is limited and based on the size of the inoculum. Until more data are available, piperacillin/tazobactam and cefepime should not be used for the treatment of ESBL K. pneumoniae.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae in community and private health care centers

In 1999, 39 of 2,599 isolates of the family Enterobacteriaceae (1.5%) collected by eight private laboratories in the Aquitaine region in France produced an extended-spectrum beta-lactamase (ESBL). Among these were 19 Enterobacter aerogenes isolates; 8 Klebsiella pneumoniae isolates; 6 Escherichia coli isolates; 3 Proteus mirabilis isolates; and 1 isolate each of Serratia marcescens, Morganella morganii, and Providencia stuartii. ESBL producers were isolated from 38 patients, including 33 residents of 11 clinics or nursing homes and 5 ambulatory patients. Seven different ESBLs were characterized. These mainly consisted of TEM-24 (25 isolates) and TEM-21 (9 isolates), but TEM-15 (2 isolates) and TEM-3, TEM-19, SHV-4, and CTX-M-1 (1 isolate each) were also characterized. Seven strains showed the coexistence of different TEM- and/or SHV-encoding genes, including a new SHV-1 variant, SHV-44, defined by the substitution R205L previously reported for SHV-3 in association with S238G. The epidemiology of the ESBL producers was investigated by random amplification of polymorphic DNA, typing by enterobacterial repetitive intergenic consensus PCR, analysis of resistance cotransferred with the ESBL, and analysis of the restriction profiles of the ESBL-encoding plasmids. Of the TEM-24-expressing strains, 18 were E. aerogenes isolates, including 9 from the same clinic, that were representatives of the epidemic clone disseminating in France. Of the TEM-21-producing strains that belonged to different species of the family Enterobacteriaceae (E. coli, K. pneumoniae, and P. mirabilis), 8 were isolated in the same nursing home. Outbreaks due to strain and/or plasmid dissemination in these clinic and nursing home were demonstrated. The presence of ESBL producers in five ambulatory patients probably resulted from nosocomial acquisition. Our data highlight the serious need to monitor patients for ESBL-producing Enterobacteriaceae in general practice.

In vitro activity of parenteral Beta-lactams, levofloxacin and tobramycin alone or in combination against extended-spectrum Beta-lactamase producing Klebsiella pneumoniae

MICs and time-kill studies were performed for four clinical isolates of extended-spectrum Beta-lactamase (ESBL)-producing Klebsiella pneumoniae. MICs (mg/L) were: piperacillin/tazobactam 8, cefepime 1-2, meropenem 0.03-0.06, levofloxacin 0.5-8 and tobramycin 0.25-32. For monotherapy, only meropenem maintained bactericidal activity over the 24 h for all isolates. Levofloxacin and tobramycin maintained bactericidal activity against the isolate susceptible to each drug. Piperacillin/tazobactam and cefepime did not maintain bactericidal activity against any isolate. Combination therapy with piperacillin/tazobactam or cefepime combined with levofloxacin or tobramycin were able to provide dramatic killing against ESBL K. pneumoniae, but did not always maintain bactericidal activity. Future studies should evaluate different antimicrobial combinations against pathogens producing specific ESBL enzymes to define their utility as an alternative to carbapenems.

Clinical and microbiologic analysis of a hospital's extended-spectrum beta-lactamase-producing isolates over a 2-year period

STUDY OBJECTIVE

To evaluate the microbiologic and clinical outcomes of patients with extended-spectrum beta-lactamase (ESBL)-producing isolates over a 2-year period.

DESIGN

Retrospective analysis.

SETTING

Tertiary care teaching hospital.

PATIENTS

Twenty-one patients with cultures of confirmed ESBL-producing Escherichia coli, Klebsiella pneumoniae, or Klebsiella oxytoca.

MEASUREMENTS AND MAIN RESULTS

Antimicrobial susceptibilities of piperacillin-tazobactam, cefotetan, carbapenems, aminoglycosides, fluoroquinolones, trimethoprim-sulfamethoxazole, and nitrofurantoin (nitrofurantoin for urinary isolates only) of confirmed ESBL producers at our institution were determined, as well as clinical outcomes of patients with ESBL-producing isolates. Microbiologic and medical records were reviewed for patient sex and age, antimicrobial susceptibilities, antimicrobial therapy, and clinical and microbiologic outcomes. From January 2000-December 2001, 31 isolates were confirmed as ESBL producers (6 E. coli, 11 K. pneumoniae, and 14 K. oxytoca). A statistically significant increase occurred over the 2-year period from 9 (0.6%) of 1414 isolates in 2000 to 22 (1.8%) of 1218 isolates in 2001 (p = 0.0055). All isolates were susceptible to carbapenems, and more than 88% were susceptible to amikacin, cefotetan, or nitrofurantoin. Less than 70% of isolates were susceptible to gentamicin, fluoroquinolones, piperacillin-tazobactam, or trimethoprim-sulfamethoxazole. All patients treated with a carbapenem experienced clinical cure. Piperacillin-tazobactam alone and in combination resulted in an overall clinical cure rate of 55%, with a 50% cure rate for isolates susceptible to piperacillin-tazobactam. All patients in whom antibiotic therapy failed had been treated with piperacillin-tazobactam or cefepime, either alone or in combination with a fluoroquinolone.

CONCLUSION

Carbapenems remain the treatment of choice for ESBL-producing pathogens. Piperacillin-tazobactam and cefepime should not be routinely administered for the treatment of these organisms.

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

Enterobacter cloacae strains from hospitalized patients with a range of infections were collected by 17 laboratories in the Asia-Pacific region and South Africa. Isolates for which ceftriaxone MICs were above 1 microg/ml and/or ceftazidime MICs were above 2 microg/ml, as well as 46 strains for which ceftriaxone and/or ceftazidime MICs were at or below these values, were screened for levels of extended-spectrum beta-lactamase (ESBL) production through the use of broth microdilution for the detection of clavulanate enhancement of the activity of ceftriaxone, ceftazidime, and cefepime. Of the isolates examined, ceftriaxone and/or ceftazidime had elevated MICs for 44%, of which 36% were ESBL positive. ESBL-positive strains were commonly susceptible to piperacillin-tazobactam and more frequently resistant to several other antimicrobials studied. A cefepime MIC above 0.25 microg/ml had the highest sensitivity (100%) and specificity (74%) for predicting the presence of an ESBL.