Prevalence and Molecular Characterization of New Delhi Metallo-Beta-Lactamases in Multidrug-Resistant Pseudomonas aeruginosa and Acinetobacter baumannii from India.

New Delhi metallo-beta-lactamase (NDM)-mediated carbapenem resistance in Pseudomonas aeruginosa and Acinetobacter baumannii is a major concern. We investigated the presence of NDM and its variants in P. aeruginosa and A. baumannii at a tertiary hospital in North India. A total of 236 isolates (130 P. aeruginosa and 106 A. baumannii) were included; 38 (29.23%) P. aeruginosa and 20 A. baumannii isolates (18.8%) were resistant to carbapenems and all of them were blaNDM positive. All 38 carbapenem-resistant P. aeruginosa harbored blaNDM-1, while 12 (60%) of 20 A. baumannii harbored blaNDM-2. Pulsed-field gel electrophoresis showed that all 58 isolates were clonally unrelated. By Southern blot analysis, blaNDM-2 was located on chromosome. The blaNDM-2-positive isolates were more frequently recovered from tracheal aspirate (67% vs.16%; p = 0.02) and intensive care unit (67% vs. 20%; p = 0.001) than blaNDM-1. Among other carbapenemases, VIM was significantly associated with blaNDM-1 than blaNDM-2 (61% vs. 17%; p = 0.006). Mortality between blaNDM-1- and blaNDM-2-infected patients was comparable. When expressed in Escherichia coli, blaNDM-2 transformant conferred one doubling dilution higher MIC value for cefotaxime, piperacillin/tazobactam than blaNDM-1. The study shows the emergence of blaNDM-mediated resistance among P. aeruginosa and A. baumannii and rapid evolution of blaNDM-2 in A. baumannii with its chromosomal localization.