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

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-blaOXA-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.

Clonal change of carbapenem-resistant Acinetobacter baumannii isolates in a Korean hospital.

The expansion of specific carbapenem-resistant Acinetobacter baumannii (CRAB) clones is a global concern due to its therapeutic difficulty and epidemicity. To understand the prevalence of CRAB isolates in a Korean hospital, we investigated the epidemiological characteristics of 96 CRAB isolates between 2016 and 2018, including the sequence types (STs), antimicrobial susceptibility, and genetic background of resistance to carbapenems and aminoglycosides. Six STs were identified using the Oxford multilocus sequence typing scheme; ST191 (n = 8), ST208 (n = 12), ST229 (n = 11), and ST369 (n = 21) were previously identified clones in the study hospital, whereas gpi variants of ST208, ST451 (n = 34) and ST784 (n = 10), were emerging clones. ST208 isolates exhibited higher resistance rates to minocycline than other ST isolates, whereas ST369 isolates exhibited lower resistance rates to aminoglycosides and trimethoprim/sulfamethoxazole than other ST isolates. All CRAB isolates previously isolated in the study hospital carried ISAbaI-blaOXA-23 for carbapenem resistance, but 10 ST229 isolates carried only ISAbaI-blaOXA-51. The carriage of armA was lower in ST369 isolates (38%) than in other ST isolates (≥83%). The frequency and diversity of aminoglycoside-modifying enzyme genes were decreased among the CRAB isolates between 2016 and 2018 compared with CRAB isolates between 2013 and 2015 at the study hospital. In conclusion, clonal complex 208 CRAB isolates are predominant in the study hospital. This study demonstrates the evolutionary change of CRAB isolates in the study hospital in relation to the emergence of new STs and selection of resistant genes.