Extended-spectrum β-lactamase producers among multiple drug resistant Escherichia coli and Klebsiella pneumoniae

Abstract

A total of 127 multiple drug resistant Escherichia coli (42) and Klebsiella pneumoniae (85) were collected from hospitals in Malaysia. These strains were tested against imipenen, cotrimoxazole, tetracycline, chloramphenicol, and other commonly used antibiotics in the group of β-lactam (penicillin and cephalosporins), quinolone and aminoglycosides. Susceptibilities were tested by disc diffusion according to the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS). These strains were also tested for susceptibilities to ceftazidime, cefotaxime and azcreonam. These strains were further tested for extended-spectrum β-lactamase (ESBL) producers with the Etest ESBL strip (AB Biodisk, Solna, Sweden). This Etest ESBL is based on the recognition of a reduction in the ceftazidime MIC in the presence of clavulanic acid. Nineteen percent of isolated E. coli and 27.0% of K pneumoniae were detected as ESBL producers. With standard augmentin and unasyn discs, the resistance percentage for E. coli and K pneumoniae isolates was 40 to 60%. This study suggests that for multiple drug resistant E.coli and K pneumoniae, the disc diffusion testing with ceftazidime, cefotaxime and aztreonam appears to be useful for detecting hyper-producers of β-lactamases, while the Etest ESBL screen test is a simple technique for validating ESBL producers.