Characterization of Airborne Microorganisms at Nationaltheatret Subway Station

Abstract

Bioaerosols containing pathogenic microorganisms can have health implications when respired. Of special concern are potential bioterrorism attacks conducted by deliberate aerosolization of hazardous toxins or pathogenic microorganisms. Investigation aiming at understanding the normal state of the bioaerosol environment is essential to facilitate detection of biological threat agents and deviations from the normal background. This MSc thesis presents a pilot study for investigation of the bioaerosol environment at a subway station in Norway. The aim of this study was to characterize airborne bacteria and Influenza virus at Nationaltheatret subway station in Oslo. A series of studies were conducted to examine the every-day concentrations and diversity of endospores and vegetative bacteria cells. Results showed that 20 times more cultivable bacteria were found during daytime compared to nighttime. An average of 400 CFUs/m3 was found in daytime samples, of which 3 % were cultivable endospore-forming bacteria. From the cultured bacteria, 92 different bacterial species were observed by tentative 16SrRNA gene identification, and 37 different bacterial genera were identified. The diversity was found to be similar during daytime and nighttime, except for decreased representation of the family taxa Bacillaceae during nighttime (6 % compared to 32 % during daytime). 402 cultured bacteria were further characterized based on observed colony morphology, hemolysis activity and antibiotic resistance. Characteristic traits of the ten most represented family taxa were found based on colony morphology. In order to include non-cultivable bacteria for characterization, performance of culture-independent analysis of total bacteria was needed. In order to facilitate such analysis, a bead mill homogenization method for efficient DNA extraction from samples containing both endospores and vegetative bacteria cells was optimized. The concentrations of total bacterial DNA in 15 different air samples were compared, and the observed pattern for daytime and nighttime concentrations resembled the concentrations found for the cultivable bacteria.Furthermore, a specific PCR assay was developed for detection and quantification of airborne Influenza A virus, and successfully verified by detection of commercial Influenza A virus particles. However, no viral RNA was found in the air samples from Nationaltheatret subway station. Inhibition of the PCR reaction was observed, and hence further investigation regarding inhibition is needed in order to rule out false negative results.