Operation of air conditioners affects the microbial pathogenic potential in bedrooms: A metagenomics and culture-dependent study

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Air conditioning is central to indoor thermal regulation and its impact on indoor microorganisms and their health implications for occupants deserve extensive investigations. While previous research has largely focused on the composition and distribution of microbial communities, microbial functions, particularly the functional genes associated with human disease have been understudied. To address this gap, metagenomic sequencing was performed to analyze the microbial compositions and functionalities in residential bedrooms located in four cities in the Yangtze River basin. A laboratory culture-dependent experiment was conducted to verify the findings of the metagenomics analysis. Our results indicate that approximately 14% of the detected microbial genes were associated with human diseases. Moreover, the relative abundances of pathogenic bacteria and functional disease-related genes were higher during the cooling period compared to the non-cooling period, and this increased with the increase in air conditioner usage. This may be attributed to the indoor temperature during the cooling period, which promoted higher bacterial survivability. The laboratory culture-dependent exp eriment also supported the correlation between air conditioner usage and pathogenic potential. Indoor relative humidity, air changes per hour, geographical location, and outdoor air pollutants were also considered, but no significant correlations were found for these factors. Our study provides a fresh perspective on microbial risks to human health by focusing on functional genes and offers suggestions to create a healthier residential environment.