The plum rain season enhances indoor airborne resistome and potential pathogen exposure.

Indoor environments are primary settings of human activity and play a central role in shaping population health through microbial exposure. However, how short-duration climatic regimes influence indoor airborne microbiomes and resistomes remains largely unknown. Here, we investigated how the plum rain season, characterized by persistent rainfall and humid conditions, affects airborne bacterial communities, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and potential human pathogens in a dormitory building. The plum rain season significantly reduced airborne bacterial richness and altered community composition, with more pronounced effects indoors than outdoors. Airborne bacterial communities during this period also exhibited less complex co-occurrence networks and broader niche breadth, suggesting season-associated changes in bacterial ecological features. Although the number of detected ARGs in indoor air remained largely unchanged, the plum rain season significantly increased the relative abundances of ARGs (3.02% vs. 1.52%) and MGEs (0.42% vs. 0.14%) indoors compared with the post-plum rain period, whereas such seasonal enrichment was not observed outdoors. Indoor air during the plum rain season also showed higher relative abundances of high-risk ARGs. Concurrently, the relative abundance of potential human pathogens increased from 7.34% to 13.38% indoors, with Achromobacter xylosoxidans being the dominant potential pathogen. Furthermore, indoor ARG enrichment was associated with higher MGE abundance, increased A. xylosoxidans abundance, and shifts in airborne bacterial community composition. Together, these findings suggest that the plum rain season promotes indoor airborne resistome enrichment and potential exposure to airborne microbial hazards, underscoring the need to incorporate regional climatic regimes into indoor environmental health assessment.