Detection of various beta-lactamases amongst gram negative bacilli from clinical isolates with special reference to Metallo beta-Lactamases

Introduction: Antimicrobial resistance is growing threat worldwide. Various resistance mechanisms have been found. ? -Lactamase antibiotics have been the mainstay of treatment for serious infections, and most active of these are carbapenems. Predominant mechanism for resistance to ?-lactam antibiotics in gram negative bacilli (GNB) is production of extended spectrum ?-lactamases (ESBLs), AmpC and Metallobetalactamases (MBLs). Aims and objectives: To detect various ?-lactamases in gram negative organisms with special reference to Metallo ?-lactamases (MBLs) from a tertiary care centre. Materials and methods: Study was carried out from December 2014 to June 2015. Total number of 569 gram negative bacilli were isolated and identified according to standard guidelines. ESBL detection was done by a screening test using Ceftazidime disc which was further confirmed by a double-disc synergy test using Piperacillin-Tazobactum/ Cefipime. AmpC were screened by a cefoxitin disc, confirmed by Cefoxitin-cefotaxime disk antagonism. Carbapenemase detection was done with Imipenem screening test which were further subjected to MBL production testing. Result: Amongst 569 isolates, 177(31.1%) were ESBL producers, 51 (9%) were AmpC producers, 31(5.5%) were ESBL and AmpC co-producers and 116(20.4%) were carbapenemase producers. Out of total 116 carbapenemase producing strains 110 (94.8%) were positive for carbapenemase production by Modified Hodge Test. In phenotypic methods for MBL production, Meropenem-EDTA disc method detected 85 (73.3%) isolates followed by Imipenem-EDTA 68 (58.6 %) and Ceftazidime-EDTA 52 (44.8%). Conclusion: It is need of the hour to standardise various cost effective and time saving methods to detect these resistance mechanisms with routine AST in Clinical Microbiology laboratory.