공기 중 부유세균 계수를 위한 최적 배양기간 결정

Objectives: Most researchers and documents used or suggested 48-hour as an optimal incubation time for colony counting of airborne bacteria but scientific basis was very limited. The aim of this study was to determine an appropriate incubation time for colony counting method used for assessing the airborne bacterial concentration. Methods: A total of 172 air samples were collected from six laboratories using tryptic soy agar plates imbedded in Andersen one-stage sampler calibrated at 28.3 L/min. All samples were incubated at the constant temperature (35℃) for 7 days. After the first 24-hour incubation, the culturable airborne bacteria (CAB) colonies were counted every 24-hour. Results: A substantial increase in the mean number of colonies was observed after 48-hour incubation regardless of the concentration levels. The number of colonies continued to increase during the 7-day incubation period but the increasing rate was steady after 2 days (p＞ 0.05) in all samples. Conclusion: This study confirmed that the 48-hour incubation time was appropriate for airborne bacterial assessment by colony counting method.