Unveiling transposon-mediated multidrug resistance in OXA-23-producing Acinetobacter baumannii ST79/ST233 subclone KL9-OCL10 in Brazil.

The global dissemination of antimicrobial resistance (AMR) is a critical public health concern. The persistence of AMR in the environmental sector, exemplified by carbapenem-resistant Acinetobacter baumannii (CRAB), underscores the critical interconnectedness between human activity, environmental contamination, and the global spread of multidrug-resistant bacterial pathogens. In this study, A. baumannii strain EW779 was isolated from a water sample from a stream impacted by anthropogenic activities in São Paulo State, Brazil, exhibited an extensive drug resistance profile, and harbored chromosome-borne blaOXA-23 gene. Genomic analysis revealed that EW779 belongs to the hospital-associated high-risk ST79/ST233 subclone KL9-OCL10. This strain harbored a wide resistome associated with mobile genetic elements such as Tn2008, Tn7::In2-4, and Tn3. Virulence genes mainly related to biofilm formation, immune evasion, and cell invasion were found, evidencing its pathogenicity as putative hypervirulent. Comparative genomic analysis revealed that many AMR and virulence traits were shared among ST79/ST233 subclone KL9-OCL10 circulating in Brazil, indicating the occurrence of a successful and potentially epidemic subclone capable of spreading across different regions. The analysis of single nucleotide polymorphism differences among all ST79/ST233 subclone KL9-OCL10 showed a genetic similarity among strains from the same Brazilian state, indicating geographic separation. These findings highlight the environmental persistence and dissemination of a hospital-associated high-risk CRAB clone, emphasizing their epidemiological importance. Therefore, this study contributes to understanding the genomic dynamics of ST79/ST233 subclone KL9-OCL10 and reinforces the need for monitoring the spread of CRAB strains across clinical and environmental settings.