Phenotypic detection of β-lactamases in enterobacteriaceae using a 12-disk procedure

Abstract

Background: Laboratory detection of various β-lactamases like extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, carbapenemases, etc., is often complicating and challenging to the clinical laboratories. The prevalence of these resistance mechanisms varies from place to place and from hospital to hospital. Aim: This study was aimed at detecting the prevalence of these resistant phenotypes among Enterobacteriaceae isolates, along with assessing the use of a 12-disk procedure for the same. Results: We found that the prevalence of ESBLs was 60%, AmpC was 10%, and carbapenemases was 12.6% in these isolates. All the strains which were pure ESBL, AmpC, or carbapenemase producers, and were picked up by the Vitek, were also detected by the 12 disc method. But in some of the strains where ESBLs coexisted with AmpC, the presence of AmpC masked the effect of clavulanate enhancement which is used for the detection of ESBLs. Conclusion: Resistant bacteria are prevalent in this hospital and this 12 disc method helps in identifying a majority of them.