Comparative genomic analysis of the bla _OXA-23 -carrying plasmids

The global dissemination of the carbapenem resistance gene bla _OXA-23 is partly facilitated by plasmids, yet a comprehensive characterization of these vectors is lacking. This study analyzed the bla _OXA-23 -carrying plasmids selected from the National Center for Biotechnology Information RefSeq database to elucidate their general characteristics and genomic diversity. The bla _OXA-23 -carrying plasmids were predominantly hosted by Acinetobacter baumannii (94.06%), and their sizes varied widely, from 8.22 to 336.05 kb. Replicon typing revealed that the majority belonged to the RP Rep family, specifically RP-T1 (62 plasmids) and RP-T2 (23 plasmids) types. A key finding of this analysis was the assignment of these two major plasmid groups to distinct plasmid taxonomic units (PTUs): all RP-T1 plasmids were classified as PTU-Pse5, whereas all RP-T2 plasmids were classified as PTU-Pse1. The bla _OXA-23 gene of the plasmids was located within four kinds of composite transposons, with Tn 2006 (33.67%), Tn 2008 (32.67%), and Tn 2009 (31.68%) being the predominant genetic contexts. Notably, the 62 plasmids of RP-T1 type (PTU-Pse5) and the 23 plasmids of RP-T2 type (PTU-Pse1), found predominantly in A. baumannii , carried genes encoding relaxases of the MOB _F family, T4CPs of t4cp2, and type F T4SS, suggesting they are putatively conjugative. In addition, the 62 plasmids of RP-T1 type (PTU-Pse5) were identified in multiple countries within the data set, while the 23 plasmids of RP-T2 type (PTU-Pse1) were predominantly found in China. These findings provide a genomic view of bla _OXA-23 plasmids, suggest their role in disseminating carbapenem resistance across species and regions, and offer a surveillance framework, highlighting key lineages for clinical intervention.

IMPORTANCE

The horizontal transfer of bla _OXA-23 to Acinetobacter baumannii and other gram-negative pathogens has conferred high-level carbapenem resistance, posing significant therapeutic challenges in both hospital and community settings. Plasmids carrying conjugative transfer systems serve as key vehicles for the dissemination of bla _OXA-23 among clinical isolates. In this study, we identified the plasmid lineages responsible for bla _OXA-23 spread and categorized them into a limited number of groups. This finding underscores the considerable risk of horizontal gene transfer in propagating carbapenem resistance and provides a valuable framework for future surveillance efforts to track the transmission of these resistant plasmids. However, this study was based on current knowledge and available data. Given the ever-changing situation of antibiotic resistance, new plasmid variants or transfer mechanisms may emerge, potentially limiting the long‑term applicability and accuracy of our findings.