Detection Of Extended-spectrum Beta-lactamases Research Articles

Avaliação da acurácia de testes laboratoriais para detecção de amostras de Klebsiella pneumoniae produtora de betalactamase de espectro estendido

Bactérias produtoras de betalactamase de espectro estendido (ESBL) representam um dos mais importantes problemas de resistência bacteriana nos hospitais brasileiros. A necessidade da implementação de testes que apresentem alta acurácia e baixo custo é de suma importância devido à dificuldade na detecção de ESBL. O objetivo do presente estudo foi avaliar a acurácia dos testes de adição de ácido clavulânico comercializados pela Oxoid® (Basingstoke, Inglaterra) e do Etest ESBL Screen® (AB Biodisk, Solna, Suécia) para detecção de K. pneumoniae produtoras de ESBL. Objetivamos também avaliar comparativamente a sensibilidade e a especificidade dos substratos betalactâmicos utilizados nestas metodologias. Foram avaliadas 134 amostras de K. pneumoniae isoladas em hemocultura de pacientes internados no Hospital São Paulo no período de julho de 1996 a julho de 2001. As amostras foram avaliadas quanto à produção de ESBL pelo teste de triagem preconizado pelo National Committee for Clinical Laboratory Standards (NCCLS), adição de ácido clavulânico (Oxoid®) e Etest ESBL Screen®. Foram consideradas produtoras de ESBL (padrão-ouro) amostras que apresentaram teste de triagem positivo e pelo menos um dos dois testes avaliados também positivo. O teste de adição de ácido clavulânico (Oxoid®) apresentou 100% de sensibilidade e 100% de especificidade, e os substratos que apresentaram melhor desempenho neste teste foram cefotaxima e cefpodoxima, ambos com 100% de sensibilidade e especificidade. O Etest ESBL Screen® apresentou 96% de sensibilidade e 100% de especificidade, sendo que a cefotaxima mostrou novamente melhor desempenho, com 92,5% de sensibilidade e 100% de especificidade. O teste de adição de ácido clavulânico (Oxoid®) apresentou excelente desempenho e pode ser facilmente implementado na rotina laboratorial por ser de alta acurácia e de fáceis realização e interpretação.

Antimicrobial Resistance Surveillance of Gram-Negative Bacteria Isolated from Intensive Care Units of Four Different Hospitals in Turkey

Background: The aim of this study was to determine the antimicrobial resistance of gram-negative rods (GNRs) isolated from surgical intensive care units and to establish the prevalence of extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IBLs). We also wished to determine the widespread beta-lactam substrate in ESBL-positive GNRs by two different E-test strips and to discuss the value of the routine utilization of these substrates together. Methods: Out of 348 nosocomial gram-negative strains isolated with similar methods, 236 strains with resistance to the beta-lactam group of antimicrobials using the E-test method were included in this study. Two different strips were used for the detection of ESBLs: cefotaxime/cefotaxime + clavulanic acid (CT/CTL) and ceftazidime/ceftazidime + clavulanic acid (TZ/TZL). For IBLs, the double-disk method was used. Results: The order of frequency of the strains, starting with the most frequent, was Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. In the 236 strains, the ESBL positivity rate was found to be 19.5% with TZ/TZL and CT/CTL strips, while it was 13.2% for IBL in 348 strains. Seventy-one percent of ESBL-positive strains gave parallel results with TZ/TZL and CT/CTL. ESBL positivity with only TZ/TZL or only CT/CTL was found to be 18 and 8%. Conclusions: Our study showed that except for imipenem, amikacin and ciprofloxacin, there was a high resistance to other antimicrobials, and multiresistance rates were increased in the strains in which ESBLs and IBLs were detected. In particular, the increasing prevalence of ESBLs in K. pneumoniae and IBLs in P. aeruginosa emphasizes the importance of the problem of infection control and antibiotic administration policies. Although it was seen that the prevalence of substrate templates in the detection of ESBL positivity was similar, we think that it is more useful to use two different strips together to obtain precise results.

Detection and Typing of Extended-Spectrum β-Lactamases in Clinical Isolates of the Family Enterobacteriaceae in a Medical Center in Turkey

To determine and type the extended-spectrum beta-lactamases (ESBLs) among the family Enterobacteriaceae in a medical center, a total of 668 clinical isolates were screened. Of the 668 isolates, the 80 strains were presumptively defined as ESBL producers according to the result of disk method using ESBL marker antibiotics (aztreonam, ceftazidime, and cefoxitin). These 80 strains were retested with the double-disk synergy test (DDST), the E-test ESBL strip, a 5-microg ceftazidime disk, and agar dilution MICs of ceftazidime with and without clavulonic acid. Isoelectric focusing was performed to confirm ESBL production and type the beta-lactamases. By evaluation of the results of all tests used for ESBL detection together with isoelectric focusing, 33 (4.9%) of the 668 isolates were described as ESBL producer. The positive results of the agar dilution test, DDST, the E-test strip, and 5-microg ceftazidime disk were 32, 26, 27, and 26 of the 33 strains, respectively. ESBL positivity was 48.8% in Klebsiella species, 15.4% in Citrobacter species, 4.9% in Enterobacter species and 1.1% in Escherichia coli strains. The ESBL enzymes frequently determined were SHV-2/6-like (pI 7.6), SHV-5-like (pI 8.2), SHV-4-like (pI 7.8), and SHV-3-like (pI 7). SHV-derived enzymes were commonly observed in Klebsiella spp whereas TEM-related enzymes were seen in E. coli strains. The results of this study indicated that SHV-2/6-derived (pI 7.6) ESBL expression among the isolates of the family Enterobacteriaceae is an important problem in our medical center.

Detection of extended-spectrum beta-lactamases in clinical isolates of Enterobacter cloacae and Enterobacter aerogenes.

The aim of the present study was to investigate the frequency of extended-spectrum beta-lactamases (ESBLs) in a consecutive collection of clinical isolates of Enterobacter spp. The abilities of various screening methods to detect ESBLs in enterobacters were simultaneously tested. Among the 68 consecutive isolates (56 Enterobacter cloacae and 12 Enterobacter aerogenes isolates) that were analyzed for beta-lactamase content, 21 (25 and 58%, respectively) possessed transferable ESBLs with pIs of 8.2 and phenotypic characteristics of SHV-type enzymes, 8 (14.3%) of the E. cloacae isolates produced a previously nondescribed, clavulanate-susceptible ESBL that exhibited a pI of 6.9 and that conferred a ceftazidime resistance phenotype on Escherichia coli transconjugants, and 2 E. cloacae isolates produced both of these enzymes. Among the total of 31 isolates that were considered ESBL producers, the Vitek ESBL detection test was positive for 2 (6.5%) strains, and the conventional double-disk synergy test (DDST) with amoxicillin-clavulanate and with expanded-spectrum cephalosporins and aztreonam was positive for 5 (16%) strains. Modifications of the DDST consisting of closer application of the disks (at 20 instead of 30 mm), the use of cefepime, and the use of both modifications increased the sensitivity of this test to 71, 61, and 90%, respectively. Of the 37 isolates for which isoelectric focusing failed to determine ESBLs, the Vitek test was false positive for 1 isolate and the various forms of DDSTs were false-positive for 3 isolates.

Detection of extended‐spectrum β‐lactamases

The susceptibility testing methods used in Denmark were evaluated with respect to their ability to detect cephalosporin resistance with cefuroxime as indicator, especially resistance caused by extended-spectrum beta-lactamases (ESBLs). Two methods for determination of minimal inhibitory concentration (MIC), three agar diffusion methods, a disc approximation test and the ESBL-Etest were used against a panel of strains producing well-known beta-lactamases. The tablet diffusion test (Rosco Neo Sensitabs) as the most used in Denmark had the lowest detection rate of cefuroxime resistance among ESBL-producing strains. The prediffusion method, which is only used at one laboratory, was the most reliable method for such detection. The MIC methods were in good agreement, but the detection rate for resistance due to ESBLs was low and depended on the antibiotics used. The disc approximation test and the ESBL-Etest both resulted in an acceptable ESBL detection rate. The latter tests discriminated between isolates producing the frequent chromosome-mediated and the in Denmark probably very rare ESBL-mediated cephalosporin resistance. For the evaluation of susceptibility tests such strains require special attention.