Comparison of conventional method and automatized vitek sysytem in the detection of extended-spectrum beta-lactamase in Escherichia coli and Klebsiella pneumoniae isolates

Abstract

Beta-lactamase production is the most important mechanism in resistance development of Gram negative bacteriae. Extended spectrum beta-lactamases (ESBL) enzymes hydrolyse penicillin and cephalosporins. Many ESBLs are derived by genetic mutation from naturally occuring enzymes. ESBL can be detected by phenotypic and genotypic methods. In our study, we compared the ESBL detection performance of automatized Vitek version 2.0 and double disk synergy among Escherichia coli and Klebsiella pneumoniae isolates which were previously detected as ESBL (+) by combined disk method at Izmir University School of Medicine Department of Medical Microbiology. The comparison of double disk synergy (DDS) and automatized Vitek system (Biomerieux, France) in ESBL positivity detection of E. coli and K.pneumoniae strains which were isolated between 30.05.2012 to 23.01.2013 at Izmir University School of Medicine Medical Microbiology Laboratory (Izmir, Turkey) was evaluated. The ESBL detection of the strains was previouly studied by combination of ceftazidime/clavulanic acid (30/10 μg) and cefotaxime/clavulanic acid (30/10 μg). 117 isolates consisted of ESBL(+) 106 E.coli and 11 K. pneumoniae. Ten (%8.5) E. coli isolates were Vitek (-) and double disk synergy (+) for ESBL detection. Three E. coli isolates were Vitek (+) and DDS (-) for ESBL detection. All of the K. pneumoniae isolates were detected positive for ESBL by both Vitek system and DDS. There are various methods in ESBL detection. Although Vitek automatized system reported false negative results in our study, it can provide rapid data for routine laboratories. We think that further studies with greater number of isolates are necessary. Key words: ESBL, cephalosporin resistance, Vitek 2, Gram negative bacteria.