New Delhi metallo-β-lactamase-producing Enterobacteriaceae, United States

Abstract

We characterized 9 New Delhi metallo-β-lactamase-producing 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 β-lactams, fluoroquinolones, and aminoglycosides, demonstrated MICs ≤1 µg/mL of colistin and polymyxin, and yielded positive metallo-β-lactamase screening results. Eight isolates had blaNDM-1, and 1 isolate had a novel allele (blaNDM-6). All 8 patients had recently been in India or Pakistan, where 6 received inpatient health care. Plasmids carrying blaNDM frequently carried AmpC or extended spectrum β-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 blaNDM fragment; all 3 were multilocus sequence type 14. Restriction profiles of the remaining New Delhi metallo-β-lactamase plasmids, including 2 from the same patient, were diverse.

Keywords: Enterobacteriaceae; NDM; New Delhi metallo-β-lactamase; United States; antimicrobial resistance; bacteria; carbapenem resistance; carbapenemase.

Figure 1

XmnI restriction analysis of New Delhi metallo-β-lactamase (NDM)–encoding plasmids, United States, April 2009–March 2011, from transformants (A) and subsequent Southern blot analysis with digoxigenin-labeled bla_NDM probe hybridized to a blot of same gel (B). Lane 1, NDM PCR product, positive control; lane 2, NDM-negative plasmid (ATCC-1705); lanes 3 and 14, 1-kb plus marker; lane 4, TF 0S-506; lane 5, TF 1100770; lane 6, TF 1100975; lane 7, TF1100192; lane 8, TF 1000527; lane 9, TF 1101459; lane 10, TF 1101168; lane 11, TF 1100101; lane 12, TF 1001728; lane 13, TF 1000654.

Figure 2

Dendrogram showing pulsed-field gel electrophoresis (PFGE) analysis and multilocus sequence typing (MLST) results for New Delhi metallo-β-lactamase–producing Klebsiella pneumoniae isolates, United States, April 2009–March 2011. Scale bar indicates % similarity. CA, California; MD, Maryland.