Air Bacterial Microbiomes in Hospitals: Case Studies from a Metropolis and a Small City of Thailand

Experimental objective: Hospital air can act as a reservoir of opportunistic and antimicrobial-resistant microorganisms, which may contribute to hospital-acquired infections. However, the composition of airborne bacterial communities and the factors shaping them within hospital environments remain insufficiently characterized. This study investigated airborne bacterial microbiomes across hospital areas and sampling approaches and compared hospitals located in a metropolis versus a smaller city in Thailand. Methods: Air samples were collected from various hospital zones using active air-pump sampling and passive air-grille or high-efficiency particulate air-filter swab approaches at King Chulalongkorn Memorial Hospital in Bangkok and Naresuan University Hospital in Phitsanulok. Microbiota were analyzed using 16S ribosomal RNA gene sequencing, followed by bioinformatic analyses. Results: Bacterial community compositions and alpha-diversity varied significantly along sampling method, hospital area, and geographic location. Passive air-grille swabs captured higher microbial biomass and diversity, consistent with accumulated microbiome deposition over time. Areas with open and semiopen ventilation (e.g., restaurant and outpatient departments) exhibited higher bacterial diversity than filtered areas (e.g., operating rooms). The metropolitan hospital showed higher abundances of Cutibacterium, Acinetobacter, Curtobacterium, and members of Comamonadaceae, whereas the hospital in the smaller city displayed greater overall diversity. High-efficiency particulate air-filter samples showed reduced diversity but enriched in spore-forming taxa. Predicted functional profiles also differed between sampling approaches and hospital locations, including pathways that might be related with human diseases. Conclusion: Hospital air microbiomes were heterogeneous and influenced by environmental conditions and sampling strategy. These findings provide insights for factor correlations and may inform improved air-quality management strategies.