Distribution of bacteria in inhalable particles and its implications for health risks in kindergarten children in Hong Kong

- The bacterial distribution and concentration in PM2.5 in kindergartens are detected with a molecular biology method.
- Inhalable bacteria genera are compared in indoor and outdoor samples.
- Health risks from airborne bacteria to kindergarten children are analyzed.

Health risks in children caused by bacteria in indoor environments have attracted much attention in recent years. There are many harmful bacteria, and children have greater health risks than adults in the same environment. To investigate the association between children's health risks and the distribution and concentration of bacteria in particulate matter smaller than 2.5 μm in indoor and outdoor air at three kindergartens in Hong Kong, quantitative polymerase chain reaction was used to determine the concentration of bacteria, and the terminal restriction fragment length polymorphism method targeting 16S ribosomal RNA genes was used to predict the phylogenetic airborne bacterial community structures. The bacterial concentrations indoors were higher than those outdoors in the three kindergartens, but no obvious differences were found (P > 0.05). Statistical analysis showed that the different schools had significantly different concentrations (P < 0.05). The abundance of bacteria in schools downtown (in Kowloon) was the greatest, reaching 3.3 × 103 to 4.95 × 104 cells per m3. However, the results showed no significant differences between the microbial populations obtained indoors and those obtained outdoors. The dominant genera were very similar among the six samples. Our results suggest that the majority of the inhalable bacteria were harmless to humans. Only a small fraction of microbial pathogens were identified, and their relative abundance appeared to increase as the concentration of particulate matter pollution increased. Analysis of these bacteria can give important clues regarding the exposure of kindergarten children to bacteria in indoor and outdoor air.

The bacterial concentrations indoors were higher than those outdoors at all three kindergartens. The higher bacterial concentration was a result of more human activities in a limited area. Our results suggest that the majority of the inhalable bacteria were harmless to humans. Only a few microbial allergens and pathogens were identified and the concentrations were very low.627