Detection of extended spectrum beta-lactamase from clinical isolates in Davangere

Extended spectrum beta-lactamase enzymes (ESBLs) are enzymes that have the ability to hydrolyze oxyiminocephalosporins and infections by isolates producing them are often difficult to treat. A study to detect the presence of these enzymes in isolates was conducted by our hospital. A total of 207 non repetitive isolates were screened for resistance to any of five screening agents. Those with suspicious profiles were checked for ESBL production by double-disk approximation or a synergy test. The isolates were also subjected to a phenotypic confirmation test as recommended by CLSI (formerly NCCLS). Various cephalosporins-beta-lactamase inhibitor combinations were also tested. Of the 204 (98.5%) screen-positive isolates, only 126 (61.7%) were identified as ESBL producers. Of these, 26.1% of the isolates were positive by using the double-disk synergy test (DDST) method alone, 13.4% were positive using the method recommended by CLSI, and 60.3% of the isolates were positive by both the DDST and CLSI methods. We also report a high percentage of resistance to cefoxitin (96.8%) indicating changes in porins.