Genetic linkage of blaNDM among nosocomial isolates of Acinetobacter baumannii from a tertiary referral hospital in northern India

The aim of this study was to evaluate the emergence of bla(NDM-1) among clinical isolates of Acinetobacter baumannii isolated from a north Indian tertiary care hospital and to assess the gene cassettes and resistance determinants located within them. In total, 74 A. baumannii were screened for MBL production by the imipenem-EDTA method and were characterised for antibiotic sensitivity. PCR was performed to detect the presence of bla(NDM) and the co-existence of ESBL and AmpC genes. NDM-producing isolates were typed by ERIC-PCR, and the association of integrons with bla(NDM-1) and the presence of gene cassettes were determined using specific primers. The genetic location of bla(NDM) in ISAba125 was also determined. Transformation was performed using a heat-shock method. Three isolates were found to harbour bla(NDM), all of which co-produced bla(EBC), bla(DHA) and bla(CIT) AmpC beta-lactamases. All MBL-producers showed resistance to cephalosporins, carbapenems, aminoglycosides, fluoroquinolones and tigecycline but were susceptible to polymyxin B. Presence of class 1 integrons was demonstrated in all three bla(NDM)-harbouring isolates, whilst linkage between the integron and bla(NDM) could not be established. Detection of gene cassettes revealed the presence of dihydrofolate reductase (dhfr) and aminoglycoside 6'N-acetyltransferase [aac(6')] genes. Presence of bla(NDM) in ISAba125 was also observed. These findings suggest that ISAba125 appears to be the main genetic component for dissemination of bla(NDM) in A. baumannii. The association of bla(NDM-1) with ISAba125 and the mobility of other multiresistance region (gene cassette)-carrying integrons provide an easy way to cross species barriers and reach a level that places the patients at risk. Crown Copyright (C) 2013 Published by Elsevier B.V. on behalf of International Society of Chemotherapy. All rights reserved.