Molecular characterization of carbapenem-resistant Enterobacteriaceae at a tertiary care laboratory in Mumbai

Carbapenem-hydrolyzing beta-lactamases are increasingly reported worldwide, leading to therapeutic failure. In an era where the drug development pipeline is stagnant, it is crucial to preserve current classes of antibiotics to help fight against infection caused by multidrug-resistant organisms (MDROs), by practicing a rational approach for the use of antibiotics. Identifying the mechanisms of resistance gives us much needed insights in this field. A total of 113 consecutive, non-duplicate carbapenem-resistant clinical isolates were collected from July to December 2012. These isolates were subjected to the modified Hodge test (MHT) for phenotypic detection of carbapenemases, an inhibitor-based test employing EDTA for the detection of metallo-beta-lactamase (MBL), and phenylboronic acid for the detection of Klebsiella pneumoniae carbapenemase (KPC). A multiplex polymerase chain reaction (PCR) assay that characterized the five most predominant carbapenemases (bla (NDM), bla (OXA), bla (VIM), bla (IMP), bla (KPC)) was designed. The 113 isolates consisted of Klebsiella spp. (46), Enterobacter spp. (32), Escherichia coli (31), Citrobacter spp. (2), Proteus spp. (1), and Morganella spp. (1). bla (NDM-1) was the most prevalent carbapenemase and accounted for 75.22 % (85/113) of the isolates. This was followed by bla (OXA) [4.42 % (n = 5)]. 18.5 % (21/113) of the isolates possessed dual carbapenemase genes. 98.9 % concordance was observed between the phenotypic tests and the molecular tests for the detection of MBL. In conclusion, patients infected with resistant bacteria require early appropriate antimicrobial treatment for good clinical outcome. Thus, identifying the resistant mechanisms of suspected pathogens becomes crucial. Also, the high incidence of plasmid-mediated bla (NDM-1) calls for the implementation of strict infection control and contact isolation precautions in order to prevent the spread of these organisms.