New Delhi Metallo-beta lactamase (NDM-1) in Enterobacteriaceae: treatment options with carbapenems compromised

Abstract

Background: Carbapenems are among the few useful antibiotics against multidrug resistant gram negative bacteria particularly those with extended spectrum beta lactamase. However resistance to carbapenems occurs and is mediated by mechanisms like loss of outer membrane proteins and production of beta lactamase that is capable of hydrolyzing carbapenems. An alert issued in the UK in 2009 warned of an increasing number of carbapenem resistant Enterobacteriaceae strains identified in UK hospital patients. Many of them were recently hospitalized in India and Pakistan and had new type of metallo beta lactamase designated as New Delhi Metallo-1 (NDM-1).

Objective: To assess the production of NDM-1 type Metallo beta lactamase enzyme in Enterobacteriaceae at a tertiary care centre in Mumbai.

Materials and methods: Consecutive carbapenem resistant Enterobacteriaceae isolates were collected from August 2009 to November 2009. Susceptibility testing for carbapenems was performed by the disc diffusion method. Carbapenemase production was confirmed by Modified Hodge test. These strains were then subjected to single target PCR. A 475bp product was amplified by the NDM primers and visualized on 3% agarose gel.

Results and conclusions: Modified Hodge test was positive for all carbapenem resistant isolates. Of 24 carbapenem resistant Enterobacteriaceae 22 were NDM producers while 2 were NDM non producers. Amongst the 22 NDM producing organisms 10 were Klebsiella spp, 9 were Escherichia coli, 2 were Enterobacter spp and 1 was Morganella morganii. This high number in a relatively short span is a worrisome trend that compromises the treatment options with the carbapenems.