Bacterial Strains
Nine clinical isolates (5 K. pneumoniae, 2 E. coli, 1 Enterobacter cloacae, and 1 Salmonella enterica serovar Senftenberg), were collected from 8 patients during April 2009–March 2011 and submitted to the Centers for Disease Control and Prevention (Atlanta, GA, USA) for reference susceptibility testing during January 2010–April 2011 (Table 1). Four patients were from California and 1 each was from Illinois, Maryland, Massachusetts, and Virginia. Species identification was confirmed with the Vitek 2 automated system (bioMérieux Vitek Systems Inc., Hazelwood, MO, USA). The S. enterica serovar Senftenberg isolate was further classified by serotyping. A previously identified NDM-1–producing K. pneumoniae isolate (0S-506) from Sweden was used as a positive control for phenotypic and molecular characterization methods, including strain typing of K. pneumoniae isolates. As part of a public health intervention for each of these isolates, an epidemiologist from CDC contacted local health departments and providers to identify characteristics of patients from whom NDM-producing isolates were obtained.