Incidence of Metallo Beta-Lactamases Producing Non-Fementers in a Tertiary Care Hospital

Introduction: In recent years, resistance to carbapenems due to metallobetalactamse production is increasing. The genes (IMP and VIM) responsible for metallo beta-lactamase (MBL) production may be chromosomally or plasmid mediated and hence poses a threat of spread of resistance by gene transfer among the Gram-negative bacteria. Therefore early identification and treatment of infections with MBL producers becomes essential.

Screening of MBL is not done as routine in our laboratory. The present study was therefore undertaken to know the incidence of MBL producing bacteria in our set up.

Aims: To study incidence of metallo-beta-lactamase (MBL) producers among nonfermenters.

Material and Methods: 315 P. aeruginosa and 170 Acinetobacter species were isolated from blood and pus samples and evaluated for carbapenem resistance and MBL production by imipenem-EDTA disc method. The inhibition zone with imipenem-EDTA disc were <14 mm for MBL-negative isolates and >17 mm for MBL-positive isolates. MBL production was confirmed by E test strip containing imipenem (4- 256 μg/ml) and imipenem(1-64 μg/ml) plus EDTA.100/10 μg).

Results: Of 315 isolates of P. aeruginosa and170 isolates of Acinetobacter, of the total 315 P. aeruginosa 265 were isolated from pus and 50 from blood cultures and out of the total 170 of Acinetobacter spp120 from pus and 50 from blood cultures were isolated. Piperacillin/tazobactam and Imipenem were the most effective antibiotics for NFGNB.

Out of the 50 Imipenem resistant isolates tested, 9 (18%) were found to be MBL producers.

Conclusions: Identification of MBL production is mandatory for making appropriate choice of antibiotics. This enables to relook into the antibiotic policy, create awareness and strengthen infection control to prevent the further spread of MBL producers.