Detection of -lactamases in nosocomial gram negative clinical isolates.

-lactamases represent the most common mechanism of -lactam resistance. Extended spectrum -lactamases (ESBLs) represent a major group of -lactamases currently being identified worldwide in large numbers along with inducible AmpC -lactamases and derepressed mutants. The present study was done to detect -lactamase production in clinical isolates by rearranging routine discs used in reporting susceptibility to specifically assess ESBLs, AmpC -lactamases (both inducible and hyperproducers i.e., derepressed mutants). A total of 286 clinical isolates were studied using a novel predictor disc approximation method to detect the above mechanisms of resistance with careful use and placement of antimicrobial discs. Of the 286 isolates, 151(53%) were ESBL producers of which 131(46%) were also derepressed mutants while remaining 20(7%) were plain ESBL producers. Forty (14%) were plain derepressed mutants. Inducible AmpC -lactamase production was detected in 19(7%) of the isolates. The commonest ESBL producers were E.coli and K. pneumoniae. The high incidence of -lactamase production due to multiple mechanisms in clinical isolates is alarming and urgent action needs to be taken from both a therapeutic and infection control perspective.