Genomic plasticity of extensively drug-resistant and multidrug-resistant Acinetobacter baumannii ST208 isolates from a fatal outbreak

Background: The prevalence of multidrug-resistant Acinetobacter baumannii (MDRA) has rapidly increased and is linked to severe nosocomial infections. MDRA outbreaks in a Japanese hospital were analysed using whole-genome sequencing. Methods: Antibiotic susceptibility testing was performed on clinical isolates from hospitalised patients before and during the 2009 and 2010 outbreaks. Whole-genome sequencing was conducted to identify acquired antibiotic-resistance genes and genetic mutations. Results: Clinical A. baumannii isolates were resistant to beta-lactams (broad-spectrum cephalosporins and carbapenems), aminoglycosides, chloramphenicol, fosfomycin, fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole. MDRA isolates harboured aac(6 ')-Ib-cr, abaF, armA, blaADC-30, blaTEM-1, and blaOXA-82, or both blaOXA-66 and blaOXA-23, catB8, mphE, msrE, and tet(B). blaOXA-82 genes were recombinationally multiplied. Quinolone resistance was also associated with gyrA S81L and parC S84L mutations. The MDRA isolates belonged to Oxford sequence type (ST) 208 and Pasteur ST2. Three of the 15 isolates developed an extensively drug-resistant (XDR) phenotype, and two isolates harboured an adeS mutation. Conclusions: We identified molecular resistance markers in three XDR and one MDR isolate and provided a genomic description of resistance and virulence, as well as the origins of the isolates. The isolates are closely related to MDRA Oxford ST208 and Pasteur ST2, identified in Asia and Australia. MDRA isolates are of concern in both hospital and community settings in the Western Pacific region. (c) 2025 The Author(s). Published by Elsevier Ltd on behalf of King Saud Bin Abdulaziz University for Health Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).