Bacterial strains producing extended spectrum beta-lactamases (ESBL) represent a common resistance problem among Brazilian hospitals. Due to the difficulty of ESBL detection in the clinical laboratory, these bacterial isolates require a reproducible, efficient, and low cost detection method. The aim of the present study was to evaluate the efficacy of detection of K. pneumoniae ESBL isolates by two methods: the Etest ESBL strip and the inhibitor potentiated disk diffusion test with clavulanic acid (clavulanate-potentiation test). The sensitivity and the specificity of beta-lactam agents against these isolates were also evaluated. The experiments were performed on a total of 134 K. pneumoniae isolates recovered from blood specimens in our institution from July 1996 to July 2001. The samples were tested for ESBL production by the NCCLS screen test, clavulanate-potentiation test and Etest ESBL strip. Isolates presenting positive results for the screen test and for at least one of the evaluated tests were considered ESBL producers (gold standard). The results of this study yielded a 100% specificity and sensitivity for the clavulanate-potentiation test, and the best indicators of ESBL production were cefotaxime and cefpodoxime. The Etest ESBL strip also turned out to be a very sensitive (96%) and specific (100%) method, being cefotaxime the most efficient substrate. According to the results of this investigation, the clavulanate potentiation disk diffusion test displayed an excellent performance and can be easily implemented in routine clinical laboratories as a practical, reliable, and accurate method.
ESBL; Clavulanate potentiation; disk diffusion; Etest ESBL Screen®
