Multiple carbapenem hydrolyzing genes in clinical isolates of Acinetobacter baumannii.

Purpose: Carbapenem resistance in Acinetobacter baumannii has become highly rampant, which has been ascribed to the presence of multiple carbapenemases. The objective of the present study was to prospectively investigate the presence of multiple carbapenemase encoding genes in clinical isolates of A. baumannii . Materials and Methods: A total of 30 imipenem resistant, consecutive non-repeat clinical isolates A. baumannii from a Tertiary Care Centre of Delhi were subjected to antimicrobial susceptibility testing (AST), screening for carbapenemase production by modified Hodge test (MHT) and determination of minimum inhibitory concentration for imipenem by E-Test ® . These were subjected to Real time PCR for bla IMP-1 and 2 , bla VIM-1 and 2 , bla OXA23, 24, 51 and 58 using SYBR green-I. These were grouped together on the basis of their genotype as each isolate harboured multiple carbapenemases and correlated with their AST profile. Detection of the novel carbapenemase bla NDM-1 was performed by real time PCR using TaqMan probes on 14 isolates. Results: Colistin appeared to be the most effective drug in vitro , followed by tetracycline and beta lactam/beta lactamase inhibitor combinations. All, but one isolate were positive for the MHT. All 30 isolates were positive for bla OXA-51 like gene as well as bla IMP-1 and bla VIM-1 genes. bla OXA 24 and 58 were not detected in any of the isolates. bla IMP-2 , bla VIM-2 , bla OXA-23 were present in 15, 6 and 14 isolates respectively. Grouping based on the genotypic profile did not correlate with susceptibility pattern. Nine among the 14 isolates also harboured the novel bla NDM-1 gene. Conclusions: This is the first study from North India, which comprehensively detected the presence of multiple carbapenemases as well the bla NDM-1 gene. The presence of the novel gene bla NDM-1 indicated ability of A. baumannii to acquire new carbapenemase genes despite the existence of multiple carbapenemase genes. The present study confirmed the presence of multiple genetic mechanisms for carbapenemases production among the clinical isolates of A. baumannii in north India.