Characterization of Airborne Bacteria at an Underground Subway Station

Abstract

The reliable detection of airborne biological threat agents depends on several factors, including the performance criteria of the detector and its operational environment. One step in improving the detector's performance is to increase our knowledge of the biological aerosol background in potential operational environments. Subway stations are enclosed public environments, which may be regarded as potential targets for incidents involving biological threat agents. In this study, the airborne bacterial community at a subway station in Norway was characterized (concentration level, diversity, and virulence-and survival-associated properties). In addition, a SASS 3100 high-volume air sampler and a matrix-assisted laser desorption ionization-time of flight mass spectrometry-based isolate screening procedure was used for these studies. The daytime level of airborne bacteria at the station was higher than the nighttime and outdoor levels, and the relative bacterial spore number was higher in outdoor air than at the station. The bacterial content, particle concentration, and size distribution were stable within each environment throughout the study (May to September 2010). The majority of the airborne bacteria belonged to the genera Bacillus, Micrococcus, and Staphylococcus, but a total of 37 different genera were identified in the air. These results suggest that anthropogenic sources are major contributors to airborne bacteria at subway stations and that such airborne communities could harbor virulence-and survival-associated properties of potential relevance for biological detection and surveillance, as well as for public health. Our findings also contribute to the development of realistic testing and evaluation schemes for biological detection/surveillance systems by providing information that can be used to mimic real-life operational airborne environments in controlled aerosol test chambers.

Indoor-Air Microbiome in an Urban Subway Network: Diversity and Dynamics

“…As the first study unraveling the microbial diversity of an urban subway network in Asia using sequencing technology, we describe the Hong Kong subway bioaerosols as taxonomically diverse, more so than was seen in previous culture-independent reports of subway microbial communities (19,21). We detected residents of various ecological habitats, including soil (Sphingobium and Acinetobacter), water (Blastomonas), and leaf (Xanthomonas).…”

“…Despite its role in modern societies, little is known pertaining to the microbial exposure of commuters during subway use. The characterization of subway bioaerosols using high-throughput, culture-independent techniques is still in its nascency, conducted with the intention of improving one's understanding of public health risks and in biodefense prepara- tion (19)(20)(21). Instead, the main focus of this study was to link patterns of observed microbial communities with intrinsic characteristics of subway usage patterns and architectural designs.…”

“…Unfortunately, the microbiological contents of the aerosol in this unique built environment are relatively unknown. The majority of current microbiological assessments of subway networks had been limited to conventional culture methods (8)(9)(10)(11)(12)(13)(14)(15)(16)(17) or limited culture-independent methods (18,19), which are likely to underestimate the true spectrum of microorganisms present. Culture-based studies are also inherently restrictive in the comparison of microbial communities between samples, as the organisms cultivated for analysis are dependent on the selective growth conditions chosen.…”

“…As a result, these studies are limited to insensitive comparisons of microbial concentrations between samples, with crude analysis on the composition of microbial communities. While these cultivation-based studies demonstrated the roles ridership (10,11,17), time (18)(19)(20), and station location and design (8,12,13,15) play in microbial concentrations and diversity in subway air, it is not known whether this difference is representative of the entire phylogenetic spectrum present given the methodologies employed. According to the only sequencing-based subway microbiome study conducted to date (21), subway air is made up predominantly of a small number of microbial phyla and families, and its community composition resembles that of outdoor air.…”

Time-Dependent Size-Resolved Bacterial and Fungal Aerosols in Beijing Subway

“…Previous studies showed a wide range of concentration levels of subway bioaerosols due to different places, seasons and different methods of sampling. Typically, the concentrations of bacterial aerosols in the subway system varied from 50 CFU m -3 to 12000 CFU m -3 , while those of fungal aerosols varied from 45 CFU m -3 to 1600 CFU m -3 (Gilleberg et al, 1998;Picco et al, 2000;Cho et al, 2002;An et al, 2004;Seino et al, 2005;Yao and Mainelis, 2006;Bogomolova and Kirtsideli, 2009;Dong and Yao, 2010;Hwang et al, 2010;Kim et al, 2011;Dybwad et al, 2012;Robertson et al, 2013;Dybwad et al, 2014;Hwang and Park, 2014). Through both culture and culture-independent methods, airborne bacterial and fungal community structures were investigated in subways (Dybwad et al, 2012;Robertson et al, 2013;Leung et al, 2014).…”