Global dissemination of imipenem-resistant (IR) clones of Acinetobacter baumannii–A. calcoaceticus complex (ABC) have been frequently reported but the molecular epidemiological features of IR-ABC in military treatment facilities (MTFs) have not been described. We characterized 46 IR-ABC strains from a dataset of 298 ABC isolates collected from US service members hospitalized in different US MTFs domestically and overseas during 2003–2008. All IR strains carried the blaOXA-51 gene and 40 also carried blaOXA-23 on plasmids and/or chromosome; one carried blaOXA-58 and four contained ISAbal located upstream of blaOXA-51. Strains tended to cluster by pulsed-field gel electrophoresis profiles in time and location. Strains from two major clusters were identified as international clone I by multilocus sequence typing.
