Phenotypic and Genotypic Characterization of Enterobacteriaceae Producing Oxacillinase-48-Like Carbapenemases, United States.

Oxacillinase (OXA)-48-like carbapenemases remain relatively uncommon in the United States. We performed phenotypic and genotypic characterization of 30 Enterobacteriaceae producing OXA-48-like carbapenemases that were recovered from patients during 2010-2014. Isolates were collected from 12 states and not associated with outbreaks, although we could not exclude limited local transmission. The alleles β-lactamase OXA-181 (bla) (43%), bla (33%), and bla (23%) were found. All isolates were resistant to ertapenem and showed positive results for the ertapenem and meropenem modified Hodge test and the modified carbapenem inactivation method; 73% showed a positive result for the Carba Nordmann-Poirel test. Whole-genome sequencing identified extended-spectrum β-lactamase genes in 93% of isolates. In all bla isolates, the gene was on a ColKP3 plasmid. A total of 12 of 13 isolates harboring bla contained the insertion sequence ΔISEcp1. In all isolates with bla, the gene was located on a TN1999 transposon; these isolates also carried IncL/M plasmids.