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(OXA-181)) (43%), bla(OXA-232) (33%), and bla(OXA-48) (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(OXA-232) isolates, the gene was on a ColKP3 plasmid. A total of 12 of 13 isolates harboring bla(OXA-181) contained the insertion sequence ΔISEcp1. In all isolates with bla(OXA-48), the gene was located on a TN1999 transposon; these isolates also carried IncL/M plasmids.