Characterization of Bioaerosols using Electron Microscopy with Special Emphasis on Airborne Bacteria
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- Institutt for fysikk 
Bioterrorist attacks on confined, indoor areas such as undergroundsubway stations by the release of pathogenic microorganisms into air,could pose a threat to public safety. The potential threat may besevere not only due to the adverse health effects themselves, but alsobecause of the lack of efficient and reliable on-site biological aerosol(bioaerosol) monitoring systems. As of the present situation, possiblebioterrorist attacks on e.g. underground subway systems may remainundiscovered until infected individuals seek medical assistance, whichmay not happen before several days after the attack. Knowledge about the morphology of bioaerosols, as they appear in air,may be important in the development of fast and reliable bioaerosol de-tectors. This study concentrates on providing such knowledge by inves-tigating and comparing different methods of characterizing bioaerosolsby electron microscopy, using aerosolized, vegetative bacteria and bac-terial spores as models. The study addresses challenges associated withelectron microscopy of bioaerosols, including dehydration artifacts andidentification of biological material in a complex, environmental sam-ple. Bioaerosol sampling is also addressed. The results of this study suggest that sampling, preservation and elec-tron microscopy of bioaerosols is more challenging than the equivalentfor non-aerosolized biological material, owing to the complex compos-ite nature of the bioaerosols, and the challenges associated with sam-pling them. Experiments with energy-dispersive X-ray spectroscopy(EDS/EDX) indicate that bioaerosols can be distinguished from inor-ganic particles in environmental samples, provided that the bioaerosolsare not associated with inorganic material. Conventional scanningelectron microscopy (SEM) does not prevent bioaerosol dehydration,and transmission electron microscopy (TEM) does not provide suffi-cient information about the morphology of bioaerosols. Critical pointdrying (CPD) is promising in some regards of bioaerosol preparationfor SEM, but preserving bioaerosol morphology as it is in air, however,is also dependent on the particles not dehydrating during sampling. Future studies are necessary to provide an optimalmethod of bioaerosolcharacterization using electron microscopy. This work however, pro-vides a comprehensive overview of the challenges faced in such regards,and presents information which may propel research into bioaerosolcharacterization and detection a small step forward.