[Sampling and detection methods of bioaerosols for the risk assessment of microorganisms in work environments]

[Bioaerosol concentrations and the identification of aerosolized bacteria by 16S rDNA analysis in work environments]

Bioaerosols cause sick building syndrome (SBS) and allergy. Many kinds of bioaerosol impactors are used for measurement of airborne microorganism concentrations in Japan. However, because the impactors are set on agar plates, some microorganisms cannot make colonies on the plates because of their lower viability or demands of nutrition. On the other hand, by double staining using ethidium bromide (EtBr) and carboxyfluorescein diacetate (CFDA), both total cells and cells with esterase activities can be detected without incubation. In this study, we calculated total cell concentrations and percentages of cells with esterase activities by the combination of filter sampling and double staining (EtBr and CFDA) from air of a laboratory, a conference room and outdoors. Temperature and humidity in the laboratory were constantly kept by an air conditioner, but in the conference room, an air conditioner was only operated sometimes because of its low frequency of use. There were no significant differences between total cell concentrations and humidity in both rooms, but increase of the percentages of cells with esterase activities depended on rainfall before the samplings (n=15, p<0.05 by Mann-Whitney test). The increase of active microorganisms by rainfall should be considered when we evaluate the risk of bioaerosols in the workplace. There were few differences in classifications of aerosolized bacteria by 16S rDNA sequence-based homology between the laboratory and the conference room. In both rooms, few pathogenic bacteria were observed.