Biological detection, identification, and monitoring (BioDIM) systems that are able to provide rapid and reliable early-warning in the event of a bioterrorism attack may contribute to reduce the impact of such incidents. Currently, few if any available BioDIM systems have been able to meet all the users’ requirements with respect to reliable, sensitive, and selective detect-towarn capabilities in different operational environments. BioDIM efforts at most real life sites must be accomplished against a naturally occurring biological aerosol (bioaerosol) background. The bioaerosol background may be both complex and variable, and could challenge the operational performance of BioDIM systems, potentially resulting in the triggering of false alarms, or even worse, the failure to respond to a real incident. One way to improve the operational performance of BioDIM systems is to increase our understanding of relevant bioaerosol backgrounds. Subway stations are enclosed and crowded public environments which may be regarded as potential bioterrorism targets, and therefore also as a relevant operating environment for BioDIM systems.
In order to improve our understanding of the bioaerosol background at subway stations, and especially how it may challenge the operational performance of BioDIM systems, the airborne bacterial background at the Nationaltheatret subway station in Oslo, Norway, was characterized in this study. Information about the concentration level, diversity, size distribution, and temporal variability of the airborne bacterial background was obtained. In addition various virulence- and survival-associated airborne bacterial characteristics such as hemolytic activity, antibiotic resistance, pigmentation, and spore fraction were investigated.
The obtained bioaerosol background characteristics were consolidated with similar and different types of existing characteristics from other subway stations, and used to define a set of realistic subway station background characteristics. Such background characteristics may be valuable when applied in a BioDIM context for several reasons. The information may be used to improve the operational performance of BioDIM systems (e.g. by optimizing alarm algorithms), but also to develop more-realistic methods for testing and evaluation (T&E) of BioDIM systems that take into account the real life background. The defined background characteristics may be used to guide the construction of realistic synthetic subway station bioaerosol backgrounds that can be recreated together with a biological threat agent aerosol challenge during simulated operational T&E of BioDIM systems in aerosol chambers. While the airborne bacterial background information mainly was intended for use in a BioDIM context in this study, it may also be relevant when viewed in the context of public and occupational health as well as microbial ecology.
An important part of this study also involved testing and implementation of sampling and analysis methods for airborne bacteria. Based on the recognized need for air samplers with well-defined performance criteria, comparative T&E of air samplers was performed in an aerosol chamber to establish their physical and biological sampling efficiencies. The obtained results revealed significant differences between the samplers, which were used to assess their suitability for various bioaerosol sampling applications.
A matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) bacterial identification method (MALDI Biotyper) was evaluated and implemented as a rapid and cost-effective screening tool for airborne bacterial isolate collections. The identification results obtained with the MALDI Biotyper were shown to correspond well with 16S rRNA gene sequencing-based results. However, the MALDI Biotyper failed to obtain reliable identifications when the reference database did not contain library entries at the corresponding species or genus level, and it was suggested that the coverage of environmental airborne bacterial taxa in the reference database should be increased.
Another BioDIM-relevant topic addressed as part of this study was rapid identification methods for Bacillus anthracis spores in suspicious powders (e.g. letters). A MALDI-TOF MS-based identification method for B. anthracis spores in powders was developed and validated. The observed performance of the analysis method demonstrated its potential applicability as a rapid, specific, sensitive, robust, and cost-effective analysis tool for resolving incidents involving suspicious powders in less than 30 min.
The work presented in this thesis contributes to a deeper understanding of the bioaerosol background, especially at subway stations. It similarly highlights the potential importance of the bioaerosol background in a BioDIM context, and emphasizes the need for increased research efforts to close existing knowledge gaps. This thesis may also serve to highlight the research efforts that will be needed before real life bioaerosol background information may be fully exploited in a BioDIM context.