Four genotypes of carbapenem-resistant Acinetobacter baumannii strains lacking OXA-23 production in Korea

During nationwide Fantimicrobial surveillance (Korea Global Antimicrobial Resistance Surveillance System [Kor-GLASS]), the recent emergence of non-oxacillinase (OXA)-23 production by carbapenem-resistant Acinetobacter baumannii (CRAB) isolates was noted. In this study, we evaluated resistance mechanisms other than OXA-23 production to elucidate the shift in considerable CRAB clones. The presence of OXA carbapenemase genes, such as blaOXA-23, blaOXA-24, blaOXA-58, and blaOXA-51-ISAba1, was determined by PCR. Other carbapenemase genes, such as blaIMP, blaVIM, blaNDM, blaKPC, blaGES, and blaOXA-48 , were determined using sequencing. Strains lacking carbapenemase genes were subjected to whole genome sequencing, and resistance genes were analyzed using ResFinder. Four CRAB strains were collected through a Kor-GLASS study in 2022, in which OXA-23 production was not identified. The carbapenemase genotypes of the four CRAB strains lacking blaOXA-23 were blaOXA-51-ISAba1, blaOXA-66/ACD25, blaOXA-182, and blaNDM-1. To the best of our knowledge, this is the f irst study to identify CRAB producing New Delhi metallo-β-lactamase (NDM)-1 in Korea. In conclusion, domestic CRAB resistance mechanisms may undergo subtle changes. Continuous observations are required to monitor the emergence of new clones.