Laboratory detection of extended-spectrum beta-lactamases (ESBLs)--the need for a reliable, reproducible method

Nosocomial Infection With Cephalosporin-ResistantKlebsiella pneumoniaeIs Not Associated With Increased Mortality

Objective.

To evaluate whether resistance to third-generation cephalosporins and/or aztreonam was associated with a higher mortality rate among patients with nosocomialKlebsiella pneumoniaeinfections.

Design.

Retrospective cohort study.

Setting.

Tertiary care university hospital.

Methods.

A total of 143 patients with nosocomial infections due toK. pneumoniaewere evaluated. Death within 21 days after diagnosis of infection was the outcome. Demographic data, invasive procedures, presence and severity of underlying conditions, infection diagnosis, anatomic site of isolation, and treatment of infection, as well as resistance to third-generation cephalosporins and/or aztreonam, were evaluated for association with the outcome.

Results.

The mortality associated with nosocomialK. pneumoniaeinfections was 22% in our study. Drug resistance was found in isolates from 48% of case patients. Multivariate analysis demonstrated that the severity of the patient's underlying condition (odds ratio, 12.50;P<.01) and isolation of the microorganism from the blood or from another usually sterile site (odds ratio, 2.94;P= .03) were associated with death. On the other hand, the presence of resistance to cephalosporins and/or aztreonam did not affect mortality, and the use of inadequate treatment was not significantly associated with increased mortality. When only the severe cases of infection were analyzed, the results were unchanged.

Conclusions.

Resistance to cephalosporins and/or aztreonam did not affect mortality, and the use of inadequate treatment was not significantly associated with increased mortality. The reasons for this are not clear. It is possible that the severity of the underlying disease and the patient's condition have a larger role than theK. pneumoniaeinfection in determining the outcome, and initially inadequate treatment may not have an impact sufficient to cause irreversible damage, allowing treatment to be changed to an effective drug.

Antimicrobial Resistance Patterns and Prevalence of blaPER-1 and blaVEB-1 Genes Among ESBL-producing Pseudomonas aeruginosa Isolates in West of Iran

BACKGROUND

Pseudomonas aeruginosa is a leading cause of nosocomial infections worldwide. Resistance of P. aeruginosa strains to the broad-spectrum cephalosporins may be caused by extended-spectrum β-lactamases (ESBLs).

OBJECTIVES

The aim of this study was to determine the antimicrobial resistance patterns and prevalence of PER-1 and VEB-1 type genes among ESBL producing strains of P. aeruginosa.

MATERIAL AND METHODS

A total of 106 P. aeruginosa isolates were collected from two university hospitals in Hamadan, Iran, during a7-month study (2009). The antimicrobial susceptibility of isolates was determined by disc diffusion method and interpreted according to the clinical and laboratory standards institute (CLSI) recommendations. Production of ESBL was determined by combined disk test and presence of PER-1 and VEB-1 type ESBL genes was identified by PCR.

RESULTS

The resistance against broad-spectrum cephalosporins and monobactames were: cefepime (97%), cefotaxime (92.5%) ceftazidime (51%), and aztreonam (27%). Ciprofloxacin (91.5%), imipenem (84.9%) and meropenem (82.1%) were the most effective anti-pseudomonas agents in this study. The results revealed that 88.7% of the isolates were multidrug resistant, 58.25% of those were ESBL positive. Sixteen (26.6%), 9 (15%) and 3 (5%) strains among ESBL-producing strains contained blaPER-1, blaVEB and blaPER-1-blaVEB, respectively.

CONCLUSIONS

This study highlighted the need to establish antimicrobial resistance surveillance networks for P. aeruginosa to determine the appropriate empirical treatment regimens. The high prevalence of multidrug resistance and production of ESBLs in P. aeruginosa isolates confirms the necessity of protocols considering these issues in the hospitals.

Prevalence and characterization of extended spectrum β-lactamases in Klebsiella-Enterobacter-Serratia group bacteria, in Algeria

OBJECTIVES

The authors had for aim to assess the local epidemiology, antibiotic resistance, and molecular typing of expanded spectrum betalactamase producing Klebsiella, Enterobacter, and Serratia (ESBL KES).

MATERIALS AND METHODS

Two hundred and seven strains of the KES group were isolated in the microbiology laboratory of the Annaba Ibn Rochd hospital in 2009. The antibiotic resistance (diffusion method and MIC) was tested and ESBL detection was performed as recommended by the Clinical Laboratory Standard Institute (CLSI). The characterization of genes for resistance to β-lactams (CTX-M-1, TEM, and SHV) and AmpC cephalosporinase (DHA-1) was performed by polymerase chain reaction. The epidemiological relationship among identified strains was analyzed by Pulsed Field Gel Electrophoresis (PFGE). Genetic transfers were performed by conjugation using sodium azide resistant Escherichia coli K(12)J(5) as recipient strain.

RESULTS

The overall incidence of ESBL KES was 31.4% (65/207) distributed as follows: 17.4% of Klebsiella spp., 7.2% Enterobacter spp., and 6.8% Serratia marcescens. The β-lactamase CTX-M 1 types were predominant (88%), followed by TEM (36.5%), and SHV (31.1%). Twenty-three strains expressed at least two bla genes. DHA-1 type cephalosporinase was found in 4 E. cloacae associated with CTX-M-1. Several epidemic clones were determined. Conjugation experiments showed that bla(CTX-M), bla(TEM), and bla(SHV) were carried by conjugative plasmids of high molecular weight (≥125kb).

CONCLUSIONS

This study revealed a high frequency of ESBL KES with a predominance of CTX-M-1. This high rate of ESBLs could be due to a clonal spread and the emergence of new epidemic clones.

Expert systems in clinical microbiology

This review aims to discuss expert systems in general and how they may be used in medicine as a whole and clinical microbiology in particular (with the aid of interpretive reading). It considers rule-based systems, pattern-based systems, and data mining and introduces neural nets. A variety of noncommercial systems is described, and the central role played by the EUCAST is stressed. The need for expert rules in the environment of reset EUCAST breakpoints is also questioned. Commercial automated systems with on-board expert systems are considered, with emphasis being placed on the "big three": Vitek 2, BD Phoenix, and MicroScan. By necessity and in places, the review becomes a general review of automated system performances for the detection of specific resistance mechanisms rather than focusing solely on expert systems. Published performance evaluations of each system are drawn together and commented on critically.

[Comparative assessment of the Vitek 2 and Phoenix systems for detection of extended-spectrum beta-lactamases]

INTRODUCTION AND PURPOSE

Detection of beta-lactam resistance in Escherichia coli and Klebsiella pneumoniae strains is clinically relevant. Moreover, it is important to differentiate between extended-spectrum beta-lactamase (ESBL) production and other mechanisms of resistance to avoid inadequate treatment of infection caused by these strains. The aim of this study was to compare the performance of the Vitek 2 and BD Phoenix automated systems for confirmatory testing of ESBL production.

MATERIAL AND METHODS

A total of 193 clinical isolates of phenotypically confirmed ESBL producers (174 E. coli and 19 K. pneumoniae) were assayed by the Vitek 2 and BD Phoenix systems using AST-N058 cards and UNMIC/ID-62 panels, respectively. The double-disk synergy test and the Etest were used as phenotype reference methods. Twelve strains characterized by genotyping were used as positive and negative controls.

RESULTS

In the clinical isolates, the sensitivity of the tests was 99.5% for Vitek and 95.3% for Phoenix. There were no significant differences between the 2 systems in the control strains. Execution of the expert system raised the sensitivity of Phoenix to 100%. However, the Vitek 2 expert system considered the results obtained in 7 strains with ESBL-positive tests to be incoherent.

CONCLUSION

Confirmatory testing for ESBL production with the Vitek 2 system (AST-N058 card) showed higher sensitivity than the Phoenix (UNMIC-ID 62 panel) system. Nevertheless, the performance of the expert systems in the 2 automated tests was similar for ESBL detection in E. coli and K. pneumoniae.

The use of antibiotic-containing agars for the isolation of extended-spectrum β-lactamase-producing organisms in intensive care units

MacConkey agar containing either cefotaxime 1.0 mg/L or ceftazidime 1.0 mg/L was evaluated for use in screening for extended-spectrum beta-lactamase (ESBL)-producing organisms. The media were evaluated using known ESBL-positive and -negative strains and 630 clinical specimens over a 6-month period. All Enterobacteriaceae isolated were identified and screened for ESBL production by phenotypic methods. In total, 14 ESBL-producing organisms were detected in the clinical samples. All known ESBL-positive strains were also detected. The use of both screening plates was required to detect all ESBLs.

Detection of extended-spectrum beta-lactamases in clinical isolates of Pseudomonas aeruginosa

With the occurrence of extended-spectrum beta-lactamases (ESBLs) in Pseudomonas aeruginosa being increasingly reported worldwide, there is a need for a reliable test to detect ESBLs in clinical isolates of P. aeruginosa. In our study, a total of 75 clinical isolates of P. aeruginosa were studied. Nitrocefin tests were performed to detect the beta-lactamase enzyme; isoelectric focusing electrophoresis, PCR, and PCR product sequencing were designed to further characterize the contained ESBLs. Various ESBL-screening methods were designed to compare the reliabilities of detecting ESBLs in clinical isolates of P. aeruginosa whose beta-lactamases were well characterized. Thirty-four of 36 multidrug-resistant P. aeruginosa clinical isolates were positive for ESBLs. bla(VEB-3) was the most prevalent ESBL gene in P. aeruginosa in our study. Among the total of 34 isolates that were considered ESBL producers, 20 strains were positive using conventional combined disk tests and 10 strains were positive using a conventional double-disk synergy test (DDST) with amoxicillin-clavulanate, expanded-spectrum cephalosporins, aztreonam, and cefepime. Modifications of the combined disk test and DDST, which consisted of shorter distances between disks (20 mm instead of 30 mm) and the use of three different plates that contained cloxacillin (200 microg/ml) alone, Phe-Arg beta-naphthylamide dihydrochloride (MC-207,110; 20 microg/ml) alone, and both cloxacillin (200 microg/ml) and MC-207,110 (20 microg/ml) increased the sensitivity of the tests to 78.8%, 91.18%, 85.29%, and 97.06%.

Antimicrobial resistance of Escherichia coli and therapeutic implications

Widespread antibiotic resistance has been recognized in Escherichia coli isolates from human, animal and environmental sources. Although prevalence rates for resistant E. coli strains are significantly distinct for various populations and environments, the impact of resistance to antimicrobial drugs is ubiquitous. This article provides information about the epidemiology, mechanisms and molecular principles of resistance, shows consequences for the antiinfective treatment of selected infections and describes measures to control the spread of antibiotic-resistant E. coli.

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.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae in an Italian intensive care unit: clinical and therapeutical remarks

In this study we evaluated the prevalence of Enterobacteriaceae and the epidemiology of ESBL+ microorganisms in an ICU of our Institution over a 5-year period and analyzed the clinical features and outcomes of the infections caused by these microorganisms. The most frequent ESBL+ isolate was Proteus mirabilis (69 isolates, 58%); a high rate of positive results in the double-disk synergy test (DDS) was also recognized for Klebsiella pneumoniae (52 isolates, 51%), whereas this phenomenon was observed less frequently in other species. In 312 cases the isolated microorganism was considered to be the cause of infection; we documented 103 wound infections, 89 UTIs, 62 LRTIs, 30 primary bacteremias, 27 infections of indwelling catheters and 1 CNS infection. The overall mortality rate due to ESBL+ strains was 1%, compared with 10.6% rate caused by ESBL-negative Enterobacteriaceae. This could be explained because ESBL+ strains caused mostly localized infections (wound infections and UTIs), whereas systemic or severe infections were sustained by ESBL-negative strains, and therapy with carbapenems was started promptly after ESBL+ isolation (always within 24h after strain isolation).

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

NCCLS screening and confirmation methods for detecting extended-spectrum beta-lactamases (ESBLs) apply only to Escherichia coli and Klebsiella spp., yet ESBLs have been found in other members of the family Enterobacteriaceae. We evaluated the effectiveness of NCCLS methods for detecting ESBLs in 690 gram-negative isolates of Enterobacteriaceae that excluded E. coli, Klebsiella pneumoniae, and Klebsiella oxytoca. Isolates were collected between January 1996 and June 1999 from 53 U.S. hospitals participating in Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology). The antimicrobial susceptibility patterns of the isolates were determined by using the NCCLS broth microdilution method (BMD), and those isolates for which the MIC of ceftazidime, cefotaxime, ceftriaxone, or aztreonam was >or=2 microg/ml or the MIC of cefpodoxime was >or=8 microg/ml (positive ESBL screen test) were further tested for a clavulanic acid (CA) effect by BMD and the disk diffusion method (confirmation tests). Although 355 (51.4%) of the isolates were ESBL screen test positive, only 15 (2.2%) showed a CA effect. Since 3 of the 15 isolates were already highly resistant to the five NCCLS indicator drugs, ESBL detection would have an impact on the reporting of only 1.7% of the isolates in the study. Only 6 of the 15 isolates that showed a CA effect contained a bla(TEM), bla(SHV), bla(CTX-M), or bla(OXA) beta-lactamase gene as determined by PCR (with a corresponding isoelectric focusing pattern). Extension of the NCCLS guidelines for ESBL detection to Enterobacteriaceae other than E. coli and Klebsiella spp. does not appear to be warranted in the United States at present, since the test has poor specificity for this population and would result in changes in categorical interpretations for only 1.7% of Enterobacteriaceae tested.

Characterization of clinical isolates of Enterobacteriaceae from Italy by the BD Phoenix extended-spectrum beta-lactamase detection method

Production of extended-spectrum beta-lactamases (ESBLs) is an important mechanism of beta-lactam resistance in Enterobacteriaceae: Identification of ESBLs based on phenotypic tests is the strategy most commonly used in clinical microbiology laboratories. The Phoenix ESBL test (BD Diagnostic Systems, Sparks, Md.) is a recently developed automated system for detection of ESBL-producing gram-negative bacteria. An algorithm based on phenotypic responses to a panel of cephalosporins (ceftazidime plus clavulanic acid, ceftazidime, cefotaxime plus clavulanic acid, cefpodoxime, and ceftriaxone plus clavulanic acid) was used to test 510 clinical isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, Providencia stuartii, Morganella morganii, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens, Citrobacter freundii, and Citrobacter koseri. Of these isolates, 319 were identified as ESBL producers, and the remaining 191 were identified as non-ESBL producers based on the results of current phenotypic tests. Combined use of isoelectric focusing, PCR, and/or DNA sequencing demonstrated that 288 isolates possessed bla(TEM-1)- and/or bla(SHV-1)-derived genes, and 28 had a bla(CTX-M) gene. Among the 191 non-ESBL-producing isolates, 77 isolates produced an AmpC-type enzyme, 110 isolates possessed TEM-1, TEM-2, or SHV-1 beta-lactamases, and the remaining four isolates (all K. oxytoca strains) hyperproduced K1 chromosomal beta-lactamase. The Phoenix ESBL test system gave positive results for all the 319 ESBL-producing isolates and also for two of the four K1-hyperproducing isolates of K. oxytoca. Compared with the phenotypic tests and molecular analyses, the Phoenix system displayed 100% sensitivity and 98.9% specificity. These findings suggest that the Phoenix ESBL test can be a rapid and reliable method for laboratory detection of ESBL resistance in gram-negative bacteria.

Antibiotic susceptibility of bacterial strains isolated from patients with various infections

AIMS

Isolates from various samples obtained during 1998 and 1999 were identified and their susceptibility to third-generation cephalosporins, monobactams and/or cephamycins studied along with any production of ESBLs.

METHODS AND RESULTS

Of these samples, bacteria most frequently isolated by the conventional techniques and Vitek GNI card were Escherichia coli (37%), Klebsiella pneumoniae (27%) and Enterobacter cloacae (16%). Using disk diffusion and double-disk synergy tests, we found that 71% strains produced ESBLs and 18% strains produced ESBLs and cephamycinases. Banding patterns of PCR amplification with the designed primers showed that 57% strains were capable of harbouring bla(SHV) genes. The bla(TEM), bla(CMY) and bla(AmpC) genes were harboured by 55%, 31% and 12% strains, respectively. Forty-five percent of strains contained more than two types of beta-lactamase genes. In particular, one strain contained bla(TEM), bla(SHV), bla(CMY) and bla(AmpC) genes.

CONCLUSIONS

The percentage of ESBL-producing strains was high. The most prevalent beta-lactamase gene was bla(SHV) gene. The bla(CMY) genes have been prevalent in cephamycin-resistant strains. The multidrug-resistant strains resistant to third-generation cephalosporins and cephamycins were detected in high percentage.

SIGNIFICANCE AND IMPACT OF THE STUDY

Resistance mechanisms to beta-lactams, comprising mostly extended-spectrum beta-lactamase (ESBL) production, lead to the resistance against even recently developed beta-lactams in enterobacteria, which is now a serious threat to antibiotic therapy. The high prevalence of bla(CMY) genes and multidrug-resistant genes may also cause therapeutic failure and lack of eradication of these strains by third-generation cephalosporins or cephamycins.

Validation of the VITEK2 and the Advance Expert System with a collection of Enterobacteriaceae harboring extended spectrum or inhibitor resistant beta-lactamases

The susceptibility testing accuracy of the VITEK2 system and the ability of the Advance Expert System (AES) to provide interpretive readings were evaluated against 86 extended spectrum (ESBL) and 6 inhibitor-resistant-TEM (IRT) beta-lactamases producing Enterobacteriaceae clinical isolates. VITEK2 MICs of 12 beta-lactams were compared with those obtained by the standard NCCLS microdilution technique. The overall essential agreement ( +/- 1 log dilution) was 87.8%. Discrepancies were mainly observed with cefepime (30.3% of total number of discrepancies), ceftazidime (21.2%), and cefotaxime (15.1%). MIC discrepancies were slightly higher in CTX-M- (14.4%) than in TEM- (12.5%) or SHV- (11.9%) type ESBL producers and were rare in IRT producers (1.4%). Overall interpretive agreement was 92.5% and minor, major, and very major errors were 5.4%, 1.7%, and 2.1%, respectively. The AES was able to identify an ESBL phenotype in 85 out of 86 isolates (98.8%) and an IRT phenotype in all 6 isolates harboring these enzymes, thus reducing very major errors to 0.9%. The VITEK2 system, in conjunction with the AES software, is a reliable tool for detection of ESBL or IRT producing Enterobacteriaceae isolates.