New Delhi Metallo-β-lactamase-1 (NDM-1): An Emerging Threat Among Enterobacteriaceae

Infections with carbapenem-resistant Enterobacteriaceae, particularly Klebsiella pneumoniae, is emerging as an important challenge in healthcare settings worldwide.1 Enterobacteriaceae isolates can display resistance to carbapenems by overexpression of Amp-C β-lactamases and extended spectrum β-lactamases (ESBLs) associated with loss of outer membrane porins; overexpression of efflux pumps; and the production of various carbapenemases including metallo-β-lactamases (MBLs; blaIMP, blaVIM, and KHM-1) and K. pneumoniae carbapenemases (KPCs).2,3 New Delhi metallo-β-lactamase 1 (NDM-1), a new type of carbapenemase, was first identified in an isolate from a 59-year-old Swedish man of Indian origin, who was admitted in New Delhi due to K. pneumoniae urinary tract infection in 2008.4 As of September 18, 2010, NDM-1 has been identified in India, Pakistan, Bangladesh, the United Kingdom, the United States, the Netherlands, Australia, Kenya, and Canada; and continues to attract great attention worldwide.4–9 This new NDM-1 has been recently identified in several Enterobacteriacae isolates causing communityonset (e.g. urinary tract infection) or healthcareassociated infections (e.g. bacteremia and ventilator-associated pneumonia).4–9 The species of the isolates harboring this enzyme included K. pneumoniae, Escherichia coli, Enterobacter spp., Citrobacter freundii, Morganella morganii, and Providencia spp.4–9 The metallo-β-lactamase gene for NDM-1 (blaNDM-1) is located on plasmids 50–350 kb in Chennai isolates, 50 kb and 118 kb in Haryana isolates, and 80–500 kb in the United Kingdom isolates.6–8 Several isolates in the United Kingdom harbor the blaNDM-1 gene, suggesting an in situ translocation of blaNDM-1. The blaNDM-1 gene, together with other coexisting resistance mechanisms, confers a high rate of resistance (>90%) to carbapenems (imipenem, meropenem, and ertapenem) and other β-lactams, aztreonam, aminoglycosides, and fluoroquinolones.4–9 The susceptibility rates of isolates from three different regions [United Kingdom (n = 37), Chennaisouth India (n = 44) and Haryana-north India