Clonal Dynamics and Antimicrobial Resistance of bla_OXA-23-Harboring Carbapenem-Resistant Acinetobacter baumannii Isolates in a Korean Hospital, 2004-2018

Carbapenem-resistant Acinetobacter baumannii (CRAB) poses a significant clinical challenge due to its epidemic potential and resistance to multiple antimicrobial agents. In Korea, bla_OXA-23 has been the predominant carbapenemase gene identified in CRAB strains since its initial detection in the early 2000s. This review analyzed the clonal evolution and antimicrobial resistance of bla_OXA-23-harboring CRAB isolates collected from a tertiary hospital in Daegu between 2004 and 2018. Over this 15-year period, substantial changes in sequence types (STs), based on the Oxford multilocus sequence typing scheme, were observed. ST353 bla_OXA-23-harboring CRAB isolates were first detected in 2004, followed by a predominance of ST92 in the mid-2000s. From 2012, ST191 and ST208 showed marked clonal expansion. Beginning in 2013, newer clones such as ST229, ST369, ST451, and ST784 emerged and gradually replaced earlier clonal lineages. These clonal shifts were primarily driven by allelic variation, particularly in the gpi gene. While most CRAB isolates exhibited an extensively drug-resistant pheno-types, susceptibility to colistin and tigecycline was largely retained. Antimicrobial resistance profiles varied by clone; for example, ST369 CRAB isolates were relatively more susceptible to aminoglycosides and trimethoprim-sulfamethoxazole. All CRAB isolates possessed the ISAba1-bla_OXA-23 genetic structure. The 16S rRNA methyltransferase gene armA was frequently detected in ST191, ST208, ST451, and ST784 CRAB, but was uncommon in ST369. These findings highlight the ongoing clonal evolution of CRAB in clinical settings and emphasize the importance of continuous molecular surveillance.