Genetic Characterization of Carbapenem-Resistant Acinetobacter spp. Isolated from Diseased Companion Animals in Japan

Carbapenem-resistant Acinetobacter spp. represent an emerging concern in human medicine; however, their epidemiology and genetic backgrounds in companion animals in Japan remain unclear. This study aimed to determine the prevalence of carbapenem resistance among Acinetobacter spp. isolated from diseased dogs and cats and elucidate the underlying genetic mechanisms.

In this surveillance study conducted as part of the Japanese Veterinary Antimicrobial Resistance Monitoring (JVARM) program, 139 isolates were collected from diseased companion animals across Japan (84 from dogs and 55 from cats) during 2020, 2021 and 2023. Antimicrobial susceptibility testing was performed for seven antimicrobials and carbapenem-resistant isolates (meropenem MIC ≥ 8 μg/mL) underwent whole-genome sequencing to identify resistance genes, genomic contexts, and associated mobile genetic elements.

Resistance rates to all tested antimicrobials were below 20%. Meropenem resistance was detected in three isolates: one from a dog and two from cats. These resistant strains were identified as A. radioresistens, A. proteolyticus, and A. johnsonii, all harboring carbapenemase genes. The A. radioresistens isolate carried chromosomal bla_OXA-23, the A. proteolyticus isolate carried bla_OXA-58, and the A. johnsonii isolate possessed a plasmid containing bla_NDM-1 and bla_OXA-58. This represents the first report of bla_NDM-1-harboring Acinetobacter isolate from companion animals in Japan.

Carbapenem-resistant Acinetobacter spp. remain rare in companion animals in Japan; however, insertion sequence mobility may promote resistance gene dissemination. As carbapenems are not approved for veterinary use in Japan, strict antimicrobial stewardship and appropriate hygiene management are essential.