New Delhi Metallo-β-Lactamase–producingEnterobacteriaceae, United States
We characterized 9 New Delhi metallo--lactamaseproducing Enterobacteriaceae (5 Klebsiella pneumoniae, 2 Escherichia coli, 1 Enterobacter cloacae, 1 Salmonella enterica serovar Senftenberg) isolates identified in the United States and cultured from 8 patients in 5 states during April 2009-March 2011. Isolates were resistant to -lactams, fluoroquinolones, and aminoglycosides, demonstrated MICs <1 g/mL of colistin and polymyxin, and yielded positive metallo-lactamase screening results. Eight isolates had bla NDM-1 , and 1 isolate had a novel allele (bla NDM-6 ). All 8 patients had recently been in India or Pakistan, where 6 received inpatient health care. Plasmids carrying bla NDM frequently carried AmpC or extended spectrum -lactamase genes. Two K. pneumoniae isolates and a K. pneumoniae isolate from Sweden shared incompatibility group A/C plasmids with indistinguishable restriction patterns and a common bla NDM fragment; all 3 were multilocus sequence type 14. Restriction profiles of the remaining New Delhi metallo--lactamase plasmids, including 2 from the same patient, were diverse. D uring the past decade, there has been an emergence of carbapenem-resistant Enterobacteriaceae that produce carbapenemases, enzymes that efficiently hydrolyze carbapenems, as well as most -lactam drugs (1). The most common carbapenemase among Enterobacteriaceae in the United States is the Ambler class A Klebsiella pneumoniae carbapenemase (KPC), an enzyme that is found through-out the United States and globally (2,3). The emergence of another group of carbapenemases, the Ambler class B metallo--lactamases (MBLs), is of great concern worldwide (4). Until recently, MBLs were rarely identified in the United States and were found exclusively in Pseudomonas aeruginosa (5). However, recent reports of K. pneumoniae producing IMP-and VIM-type MBLs (6,7) have increased concerns over additional transmissible carbapenem resistance mechanisms in Enterobacteriaceae.