Clonal evolution and antimicrobial resistance of Acinetobacter baumannii isolates from Korean hospitals over the last...

The wide-spread of drug-resistant Acinetobacter baumannii is a global health problem. This study investigated the clonal distribution and antimicrobial resistance of 167 A. baumannii isolates from two Korean university hospitals from 2009 to 2019 by analyzing the sequence types (STs), antimicrobial resistance, and resistance determinants of carbapenems and aminoglycosides. Twenty STs, including 16 pre-existing STs and four unassigned STs, were identified in A. baumannii isolates using the Oxford multilocus sequence typing scheme. Two STs, ST191 (n = 77) and ST451 (n = 40), were prevalent, and majority (n = 153) of the isolates belonged to clonal complex 208. The ST191 isolates were detected during the study period, whereas ST451 isolates were detected after 2016. One hundred forty-seven (87%) of 167 A. baumannii isolates were non-susceptible to carbapenems. The ST191 and ST451 isolates exhibited higher resistance to antimicrobial agents than that of the sporadic ST isolates. Interestingly, ST451 isolates exhibited lower susceptibility to minocycline and tigecycline than the other ST isolates. All carbapenem-non-susceptible A. baumannii isolates, except four, carried the ISAbaI-bla_OXA-23 structure. armA was detected in all amikacin-non-susceptible isolates (n = 128) except for one isolate. Five aminoglycoside-modifying enzyme (AME) genes were detected, but their carriage varied between STs; ant(3″)-Ia and aac(6')-Ib were more common in ST191 than in ST451, while aph(3')-Ia was more common in ST451 than in ST191. This study demonstrated the clonal evolution related to antimicrobial resistance in A. baumannii.