We characterized 9 New Delhi metallo-beta-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 beta-lactams, fluoroquinolones, and aminoglycosides, demonstrated MICs ≤1 microg/mL of colistin and polymyxin, and yielded positive metallo-beta-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 beta-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-beta-lactamase plasmids, including 2 from the same patient, were diverse.

Of the 9 vancomycin-resistant Staphylococcus aureus (VRSA) cases reported to date in the literature, 7 occurred in Michigan (MI). In 5 out of 7 of the Michigan VRSA cases, an Inc18-like vanA plasmid was identified in the VRSA isolate and/or an associated vancomycin-resistant Enterococcus (VRE) isolate from the same patient. This plasmid may play a critical role in the emergence of VRSA and analysis of the geographical distribution of VRE containing this plasmid may explain the observed prevalence of VRSA in MI. A total of 1,641 VRE from three separate collections were tested for the Inc18-like vanA plasmid by PCR for traA, repR, and vanA. All VRE from 2 MI institutions (N= 386), and between 60 to 70 VRE (N=883) from 17 institutions in 13 other states were tested. Fifteen isolates (3.9%) from MI were positive for an Inc18-like vanA plasmid (9 E. faecalis [12.5%], 3 E. faecium [1.0%], 2 E. avium, and 1 E. raffinosus). Six isolates (0.6%) from outside of MI were positive (3 E. faecalis [2.7%] and 3 E. faecium [0.4%]). Fourteen of the 15 plasmid-positive isolates from MI had the same Tn1546 insertion site location as those of the VRSA-associated Inc18 plasmid whereas 5 out of 6 plasmid-positive isolates from outside of MI differed in this characteristic. The one exception was an E. faecium isolate with a pulsed-field gel electrophoresis (PFGE) pattern that was indistinguishable from a plasmid-positive isolate from MI. Most plasmid-positive E. faecalis demonstrated diverse patterns by PFGE, with the exception of three pairs with indistinguishable patterns, suggesting the plasmid is mobile. Although VRE with the VRSA-associated Inc18-like vanA plasmid were more common in MI, they remain rare. Periodic surveillance of VRE for the plasmid may be useful in predicting occurrence of VRSA.