2016 Volume 19 Issue 2 Pages 99-110
To explain influences of airborne microorganisms in a university rooms, we studied the seasonal changes of concentration (cfu/m3 and cells/m3), I/O ratio (In/Out ratio), identification of Gram-positive cocci and sources of airborne fungi and bacteria.
The concentrations of airborne bacteria and fungi, in the three rooms, that is a conference room, a practice room, and a laboratory, and outdoor of a university, were measured by the impaction method and the filtration method once a month during two and a half years. Viable fungi concentration (cfu/m3) in the rooms exceeded the standard value of Architectural Institute of Japan (AIJES-A0002-2013, Office: 50 cfu/m3≧) from summer to autumn every year, suggesting that the fungi were inflowing from outside air through the air conditioning system. A high value of viable fungi concentration was observed in Jul. 2012, but such high concentration was not recognized after that and no generation sources were recognized in this room. On the other hand, viable bacteria concentrations were almost satisfied AIJES-A0002-2013 (Office: 500 cfu/m3≧) during the same period. But, in the laboratory and the conference room that were frequently used, I/O ratios of viable bacteria often exceeded over 1, suggesting that the source of fresh bacteria was in the room. Moreover, most of I/O ratios of bacteria obtained from total cell concentration (cells/m3) were not greater than 1. Therefore, measurement of airborne bacteria by the impaction method was considered to be suitable for understanding relatively recent influences.
Based on Gram staining, composition of bacteria detected in the room was simple compared to outdoor, and there were many Gram-positive cocci, such as Staphylococcus spp including S. epidermidis and S. hominis, and genus Micrococcus by api test, from the frequently used rooms. Accordingly, it was strongly suggested that sources of those bacteria were occupants.
