Variations in plasmid transfer in Acinetobacter baumannii: insights from epigenetics, strain properties, and...

Plasmid-mediated horizontal gene transfer is a driver of antibiotic resistance dissemination in Acinetobacter baumannii. Here, we investigated the extent to which intrinsic host factors influence plasmid uptake across diverse A. baumannii isolates using electro-transformation and conjugative transfer assays. To enable comparisons, electro-transformation conditions were optimized to minimize technical variability and reveal strain-dependent differences in plasmid uptake. Under the conditions used here, substantial variation in transfer efficiency was observed, including between closely related strains, indicating that plasmid acquisition is strongly influenced by the recipient genetic background. Comparative analyses of electro-transformation and conjugation demonstrated that while experimental parameters such as competent cell density, DNA input, and recipient-to-donor ratios affect transfer efficiency, these factors do not overcome inherent strain-specific barriers. Genome and methylome analyses also revealed extensive diversity in restriction-modification systems and DNA methylation patterns among recipient strains. Moreover, plasmids exhibited altered methylation profiles following transfer into new hosts, consistent with host-driven epigenetic modification. These findings indicate that plasmid transfer efficiency in A. baumannii is determined primarily by strain-specific genetic and epigenetic features rather than transferable experimental conditions. This variability has important implications for interpreting plasmid mobility, host range, and resistance dissemination within this clinically significant species.IMPORTANCEPlasmid-mediated gene transfer is one of the major drivers of antibiotic resistance in Acinetobacter baumannii; however, plasmid transfer protocols remain inconsistent and strain-dependent. By assessing electroporation and conjugation across diverse strains, we identify key experimental and genomic factors, such as test and strain differences, including restriction-modification systems and epigenetic signatures, that influence plasmid uptake. These findings offer practical guidance for optimizing plasmid transfer protocols and highlight strain-level barriers that impact resistance gene dissemination in this critical microorganism.