Relationship between culturable airborne bacteria concentrations and ventilation systems in underground subway stations in Seoul, South Korea

In this study, we evaluated the concentrations of culturable airborne bacteria (CABs) in the underground environment of 16 subway stations in Seoul, South Korea. The effects of environmental factors on CAB distributions and concentrations, including temperature, relative humidity, depth, year of construction, number of subway passengers, and ventilation, were investigated. Tryptone soy agar was used as the culture medium. Isolated bacteria were initially characterized according to cell morphology and Gram staining and then further characterized using the VITEK 2 XL microbial identification system. There were significant correlations between CAB concentrations and station temperature, depth, and construction year. Micrococcus and Staphylococcus species accounted for 66 % of the total number of CABs identified. CAB concentrations in stations with ventilation systems were significantly lower than those in stations without ventilation systems (p < 0.001). Thus, it is critical to develop techniques to improve indoor air quality in subway stations with no ventilation system.