Structural characteristics of pathogenic bacteria in split-type air conditioners and environmental factors related to their pathogenicity

Split-type air conditioners (SAC) are widely used worldwide. However, current research primarily focuses on aspects such as the energy consumption, operational efficiency, and human behavior of split-type air conditioners, with limited studies on microbial community within these systems. Additionally, research on microbial community in centralized air conditioning systems mainly focuses on the total bacterial community level, lacking studies on pathogenic bacterial community. Therefore, we investigated the characteristics of total bacterial and pathogenic bacterial community structure in SAC and the environmental factors affecting their community structure. The results reveal a significant presence of potential pathogenic bacteria within the bacterial community on SAC filters, ranging from 6.0 % to 41.8 %. Consistently, functional phenotype analysis shows a potential pathogenicity of the bacterial community reaches 29.2 %. Additionally, residential SAC filters exhibit higher diversity and abundance of pathogenic bacterial communities compared to office environments, while the potential pathogenicity of bacterial communities in offices is higher than in residential settings. Redundancy analysis (RDA) indicates that ventilation duration, air conditioning operating time, air conditioning set temperature, the floor of the room, the number of plants and occupants collectively explain 31.3 % and 22.7 % of the variations in total bacterial and pathogenic bacterial communities, respectively. Ventilation duration is identified as the key factor influencing both the structure and pathogenicity of bacterial communities. From the perspective of microbial interaction networks, increased ventilation not only enhances diversity but also introduces more competitive interactions, challenging the survival of pathogens and consequently reducing the potential pathogenicity of bacterial communities.