Survey of airborne bacterial genus at a university campus

Indoor airborne bacterial concentrations were measured at different locations in a university campus in Hong Kong where there was a Mechanical Ventilation and Air-conditioning (MVAC) system. Total bacterial counts were enumerated for both indoor and outdoor areas at specific time intervals. Information on temperature, relative humidity, number of occupants, and carbon dioxide levels were recorded simultaneously. Those parameters were correlated with total bacterial counts and each identifiable genus. Although, the number of genera for Gram-negative bacteria was higher than Gram-positive bacteria, the most abundant airborne genera found were Gram-positive bacteria especially Micrococcus and Staphylococcus. The indoor-to-outdoor ratios for the two predominant Gram-positive genera were greater than one, indicating that the source of the bacteria was indoors. There was a correlation between total bacterial counts with temperature, but the correlation was not significant. Pseudomonas had a correlation with relative humidity, but the correlation was not significant. The study also found that the total bacterial counts and a few genera including Staphylococcus and Pseudomonas, had a strong correlation with ventilation.