Release of bacterial aerosols from air conditioning system in office buildings

Microbial reproduction in air conditioning (AC) systems has caused increasing concern. When subject to airflow, microbes can be separated from substrates and spread into indoor air. This study investigated release of bacterial aerosols from AC systems with different service times in office buildings. Microbial aerosols were collected onto sterilized polycarbonate membranes using an air sampler. The concentration of total bacterial DNA was determined by 16S qPCR targeting universal bacterial genes. The most abundant genus was Lactobacillus before turning on the AC system. After turning on the AC system, the abundant genera were Pseudomonas and Agrobacterium with the service time of three and 12 years. When the AC system was put into use in the early stage, the microbial concentration after turning on the AC system was lower than that before turning on the AC system. However, after a long use of the AC system, the microbial concentration after turning on the AC system (7.50 × 103 copies/m3) was higher than that before turning on the AC system (3.77 × 103 copies/m3). The results show that the service time of AC system influences the community structure and content of indoor bacterial aerosols.