Abstract
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 bla(NDM) positive. All 38 carbapenem-resistant P. aeruginosa harbored bla(NDM-1,) while 12 (60%) of 20 A. baumannii harbored bla(NDM-2). Pulsed-field gel electrophoresis showed that all 58 isolates were clonally unrelated. By Southern blot analysis, bla(NDM-2) was located on chromosome. The bla(NDM-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 bla(NDM-1). Among other carbapenemases, VIM was significantly associated with bla(NDM-1) than bla(NDM-2) (61% vs. 17%; p = 0.006). Mortality between bla(NDM-1)- and bla(NDM-2)-infected patients was comparable. When expressed in Escherichia coli, bla(NDM-2) transformant conferred one doubling dilution higher MIC value for cefotaxime, piperacillin/tazobactam than bla(NDM-1). The study shows the emergence of bla(NDM-)mediated resistance among P. aeruginosa and A. baumannii and rapid evolution of bla(NDM-2) in A. baumannii with its chromosomal localization.