Screening and confirmatory assays for detection of ESBLs (extendedspectrum ß-lactamases) production by Klebsiella pneumoniae isolates

Abstract

ESBLs (extended-spectrum ß-lactamases) are enzymes produced by Enterobacteriaceae, especially Klebsiella pneumoniae, which mediate resistance to extended-spectrum ß-lactams and aztreonam. Considering the importance of detecting ESBLs producing strains, in this study, usual screening and confirmatory assays were compared. One hundred and seven strains of K. pneumoniae, isolated from patients with urinary tract infection, were screened for ESBLs production according to NCCLS 2005 guidelines, using broth microdilution in the Microscan Walkaway (Dade Behering) and Kirby-Bauer disk diffusion (KBD) test. Fifty-five strains selected as possible ESBL producers (51,4%), were submitted to confirmatory assays: E-test, double disk (DD) approximation and clavulanic acid (CA) association. Production of ESBLs was detected by the five methods used in 38 (69%) strains and 10 (18,2%) were negative only in DD. Seven strains (12,7%) did not present suggestive breakpoints in the Microscan Walkaway and were negative in the DD test, whereas the KBD values for the same strains obtained were indicative of ESBLs production. These results suggest that the combination of KBD breakpoints determination and CA association can be used as an efficient, alternative and less expensive system than the E-test.