Phenotypic methods for detection of Amp C b lactamases in Gram negative clinical isolates of a tertiary care hospital

Abstract

: ESBLs (Extended spectrum beta lactamases) are detected routinely in most laboratories but Amp c Beta lactamases are neglected to large extent. Pseudosusceptibility seen in Amp C producers leads to resistance to extended-spectrum cephalosporins resulting in inappropriate antimicrobial regimens and therapeutic failure. Thus, there is a need to know an appropriate phenotypic method for easy detection of Amp C β-lactamases as they have clinical relevance.: To detect and compare different phenotypic methods for Amp C β-lactamases in Gram-negative clinical isolates of Enterobacteriaceae familyA prospective study was done at Mamata Medical college, Khammam for period of three months. Phenyl boronic acid method, Cefoxitin Cloxacillin-Double disc synergy test, TRIS EDTA method, Disc approximation test were done on isolates after screening by Cefoxitin disc.: Out of 140 isolates tested, 80(57%) were positive (resistant) for screening test by cefoxitin. Out of them 61(76.2%) were Escherichia coli, 16 (20.1%) isolates were Klebsiella pneumoniae and 3 (3.75%) were Enterobacter sp. Phenotypic confirmatory methods by Cefoxitin Cloxacillin Double disc Synergy (CC-DDS) test showed zone difference of >4mm in 38(47.5%) isolates , by Phenylboronic acid method (PBA) > 5mm zone difference was observed in 34(42.5%) isolates, by TRIS EDTA method 32 (40%) showed indentation near EDTA disc and by Disc approximation test 32(40%) were positive for Amp C production. E coli was the commonest isolate showing Amp c production by all four methods.: CC-DDS method has better detection rate compared to other phenotypic confirmatory methods. We suggest CC-DDS method as it is easy to perform.