Experimental snapshot of cultivable airborne bacteria at a Czech subway station

Monitoring systems for rapid airborne biothreat detection experience performance degradation in environments with a complex, dynamic bioaerosol background. Knowledge about bioaerosol backgrounds may therefore help improve the performance of such systems. Subway stations are enclosed public environments regarded as potential bioterrorism targets. This study describes for the first time a snapshot of cultivable airborne bacteria (CAB) at a Czech subway station. The airborne bacterial concentration level and diversity was investigated and directly compared with previous observations made at a Norwegian subway station using a similar experimental approach. The CAB level ranged from 101 to 102 colony forming units (CFU) m-3, which was within the observed range in Norway. However, the average level was approximately three times lower than in Norway. The diurnal concentration profile showed increased levels during rush hours compared to non-rush hours and decaying evening levels, consistent with the Norwegian profile. The bacterial genera Micrococcus, Bacillus, and Staphylococcus, previously shown to be abundant in Norway, corresponded to ~80 percent of the CAB at the station. Interestingly, nearly all the observed genera had also been encountered in Norway. The bacterial diversity was investigated using the MALDI Biotyper (MALDI-TOF MS), and its applicability as a rapid, cost-effective classification method for bacterial isolates was confirmed. This study demonstrated that very similar CAB backgrounds can be encountered at different European stations (Czech Republic and Norway), and that anthropogenic activities (mainly passengers) appear to be a major CAB source. The outcome of this work has relevance for public and occupational health as well as microbial ecology. In addition, it may potentially be used to improve the performance of biothreat detection systems and contribute to the development of more realistic test methodologies for such systems.