A hidden reservoir of antibiotic resistance genes: transferable plasmids in community air and wastewater

Plasmid-mediated dissemination of antibiotic resistance genes (ARGs) poses a major public health threat. In contrast to the well-studied resistance plasmids within pathogens, those from non-pathogenic environmental reservoirs remain underexplored. Here, we characterized transferable multidrug-resistant plasmids captured from community air and wastewater via conjugation assays. Transconjugants obtained from these environmental samples were profiled phenotypically against 17 antibiotics and genetically via short- and long-read sequencing. Conjugative plasmid transfer was successfully captured from 33 (20.6%) of 160 environmental samples, yielding 78 transconjugant isolates and 40 plasmid types. The captured plasmids conferred resistance to 4–18 antibiotics, with near-universal resistance to ampicillin (98.7%) and retained susceptibility to polymyxin B (84.6%). Among 150 ARG instances identified across 19 classes, aac(3)-IId was the most prevalent. The dominant plasmids ps15D023_8 (wastewater) and peccDNA113 (airborne) were particularly notable; peccDNA113 carried 4 ARGs, 9 virulence factors (including fimH and AcrB ), and confers resistance to at least 7 antibiotics. Critically, the carbapenemase gene blaNDM-5 was detected, and peccDNA113 shows homology to clinical plasmids, indicating a high risk of clinical–environmental exchange. These findings highlight community environments as crucial reservoirs for mobile, high-risk resistance plasmids and underscore the urgent need for expanded surveillance beyond clinical settings.