Assessment of airborne bacteria and fungi in different-type buildings in Nanjing, a hot summer and cold winter moist Chinese city

Airborne bacteria and fungi in different buildings have unique health effects, which demands comparisons of their characteristics to provide a targeted reference for bioaerosol standards. We applied the culturable method and next-generation sequencing technology to characterize the airborne bacteria and fungi in 28 residences, 4 schools, 2 office buildings and 1 hospital during summer and winter in Nanjing, China. A total of 222 rooms, 1029 culturable microbial samples, and 203 sequencing samples were investigated. Results showed that there were significant disparities in bioaerosol concentrations and communities among various buildings and seasons. In contrast, the size distribution of bioaerosols showed little difference, with 78.6% of bioaerosols in the respirable fraction (1) of bacteria and fungi in summer. Pathogenic bacteria (Acinetobacter lwoffii, Bacteroides fragilis and Acinetobacter baumannii) and fungi (Candida albicans, Malassezia restricta and Aspergillus flavus) were dominant in indoor pathogens. The correlation analysis showed that indoor temperature, relative humidity, CO2, and outdoor bioaerosols could influence indoor bioaerosol levels. Results in this study provide valuable data on bioaerosol profiles in various built environments and highlight the significance of measuring and evaluating the concentration, size and species of bioaerosols simultaneously, which may help in the formulation of indoor bioaerosol standards in China. •Bacteria and fungi in four-type buildings during summer and winter were compared.•Non-carcinogenic risks of bioaerosols were assessed.•Pathogens at the species level were investigated in built environments.•Outdoor bioaerosols and environmental conditions could influence indoor bioaerosol.•Hospitals and kindergartens should be paid more attention to maintain air quality.