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

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 .