Clonal diversity of New Delhi metallobetalactamase-1 producing Enterobacteriaceae in a tertiary care centre

Abstract

New Delhi metallobetalactamase-1 (NDM-1) production is a major mechanism of resistance to carbapenems among the Enterobacteriaceae and is a cause for concern in the field of microbial drug resistance. This study was performed to detect NDM-1 in Enterobacteriaceae and to determine the clonal relatedness of NDM-1 producing Escherichia coli and Klebsiella pneumoniae isolated from patients admitted in a tertiary care centre. A total of 111 clinically significant Enterobacteriaceae isolates, resistant to cephalosporin subclass III were screened for carbapenemase production by the modified Hodge test. Minimum inhibitory concentration to imipenem and meropenem was determined and interpreted according to Clinical Laboratory Standards Institute 2011 criteria. Presence of bla NDM-1 was detected by polymerase chain reaction. To ascertain clonal relatedness, random amplification of polymorphic deoxyribonucleic acid (RAPD) was carried out for representative NDM-1 producers. bla NDM-1 was detected in 64 study isolates, of which 27 were susceptible to carbapenems. RAPD revealed a high degree of clonal diversity among NDM-1 producers except for a small clustering of isolates in the neonatal intensive care unit. There is extensive clonal diversity among the NDM-1 producing E. coli and K. pneumoniae. Hence, antibiotic selection pressure rather than horizontal transfer is probably an important operating factor for the emergence of NDM-1. This calls for increased vigilance, continuous surveillance and strict enforcement of antibiotic policy with restricted use of inducer drugs.