Putative conjugative transfer and persistence of carbapenem resistance gene bla OXA-72 from Acinetobacter pittii to Acinetobacter baumannii

ABSTRACT Carbapenem-resistant Acinetobacter (CRA) has been associated with increased morbidity and mortality in clinical settings. In this study, we explored the transfer potential of a mobilizable plasmid-harboring bla OXA-72 gene between Acinetobacter species originating from patients, municipal wastewater, and pig farm wastewater. PCR-based evidence suggested putative transfer of bla OXA-72 from Acinetobacter pittii to Acinetobacter baumannii . In this pair, the apparent frequency of PCR-marker-positive putative transconjugants varied depending on temperature and meropenem supplementation, with a higher frequency observed at 27°C than at 17°C and 37°C. Likewise, the presence of antibiotic pressure yielded a higher apparent conjugation frequency; however, this observation was limited to a single donor-recipient pair. Further, we revealed a phenotypic conversion in terms of meropenem susceptibility and a fitness cost in the putative transconjugants. While whole-genome sequencing did not conclusively verify the presence of bla OXA-72 or a fully resolved plasmid configuration, Oxford Nanopore read mapping consistently detected the chromosomal strA gene in all isolates. In contrast, only a limited number of reads aligned with the bla OXA-72 gene, traC , or the complete plasmid sequences. Comparative analyses further revealed variations in the composition of surface-associated factors and defense systems of the recipient strains, which could be considered as barriers to conjugation. Lastly, the persistence of PCR-detectable marker genes in putative transconjugants was variable and generally unstable over a 30-day period. Overall, these findings provide preliminary insights into the factors that may influence horizontal gene transfer and short-term maintenance of bla OXA-72 . IMPORTANCE Carbapenem-resistant Acinetobacter (CRA) is a serious clinical concern linked to elevated morbidity and mortality. This study shed light on how the carbapenemase gene bla OXA-72 spreads in the environment via horizontal gene transfer. Using isolates of Acinetobacter pittii and Acinetobacter baumannii from municipal wastewater treatment plants, we show that PCR-based evidence of putative conjugative transfer of the bla OXA-72 gene depends on temperature and antibiotic exposure. The process also incurs fitness costs, and the transferred gene persists only briefly in recipient cells. These results emphasize the importance of environmental sources as reservoirs for antimicrobial resistance gene exchange. Additionally, variations in surface structures and defense systems may act as potential barriers to conjugation. Overall, the work improves our understanding of antimicrobial resistance (AMR) movement and supports the need for better integrated surveillance under a One Health approach.