Molecular detection of bla NDM-1 (New Delhi metallobetalactamase-1) in nosocomial Enterobacteriaceae isolates by nested, multiplex polymerase chain reaction.

Background: Carbapenems are considered "drugs of last resort" in many life-threatening infections. Advent of carbapenemases like KPC, OXA-48, VIM, IMP, and NDM have greatly affected the efficacy of these drugs, posing serious threat to global health and infection control. NDM bears special significance to the India subcontinent, labeled as place of origin and reservoir. NDM tends to escape detection by routine phenotypic methods, requiring molecular confirmation. This study utilizes nested, multiplex polymerase chain reaction (PCR) for reliable detection of bla NDM-1 in nosocomial Enterobacteriaceae isolates.

Methods: This study was conducted to detect prevalence of bla NDM-1 , bla IMP , bla VIM and bla KPC genes by multiplex PCR among multidrug/carbapenem-resistant nosocomial Enterobacteriaceae isolates. From March 2013 to April 2014, 100 consecutive non-repeat isolates of Enterobacteriaceae from various inpatient clinical samples were analyzed. Imipenem-resistant isolates identified by Kirby Bauer disk diffusion method with Clinical and Laboratory Standards Institute guidelines were further subjected to nested, multiplex PCR to simultaneously detect bla NDM-1 , bla IMP , bla VIM and bla KPC genes.

Results: Out of 100 isolates, 17 (17%) were found to be imipenem-resistant. bla NDM-1 was detected in all 17 isolates by nested, multiplex PCR. bla VIM was co-carried in 4 isolates while one isolate co-harbored bla IMP with bla NDM-1 . Imipenem resistance and NDM-1 carriage was predominant amongst Klebsiella isolates. Maximum NDM-1 producers were isolated from the intensive care unit (70.6%).

Conclusion: NDM-1 prevalence in nosocomial Enterobacteriaceae isolates in our hospital was found to be 17%. A nested, multiplex PCR was used for rapid detection of various carbapenemase genes with high sensitivity and specificity which is essential not only for favorable patient outcome but also for timely implementation of appropriate infection control practices to prevent further spread of such organisms.