Inactivation of Airborne Bacteria by Direct Interaction with Non-Thermal Dielectric Barrier Discharge Plasma: The Involvement of Reactive Oxygen Species

The present study examined the effect of Dielectric Barrier Discharge (DBD) plasma on bioaerosol particles. Different DBD plasma devices were designed and tested for their efficacy in inactivation of airborne bacteria. Bacterial aerosols were injected in / through the plasma stream and the treated bioaerosols were analyzed. The results indicated a complete inactivation of bioaerosol upon a very short exposure in the range of milliseconds to plasma discharge. A large system was designed to evaluate its efficacy to inactivate bacterial spores. After preliminary studies, to study the underlying mechanisms of inactivation, a single filament DBD plasma generating probe was developed and used for subsequent studies. In parallel, a near uniform aerosol generator (nebulizer) was optimized, and aerosol particle size characterized. The kinetics of bacterial inactivation produced by this system was investigated, and sub-lethal dose determined. We hypothesized that the prototype bacteria, Escherichia coli when present in aerosols and exposed to single filament DBD plasma system, activates intracellular reactive oxygen species (ROS). The predetermined sub-lethal dose of DBD plasma was used to study the cellular responses of Escherichia coli during its inactivation. Cell membrane is more vulnerable when bacteria are present in aerosols, and hence the changes in features, such as cellular respiration and growth, permeation, and depolarization were investigated following exposure to single filament DBD plasma system. During studies, the catalase mediated defense system was found to be involved predominantly in the management of intracellular ROS pool. Through the use of E. coli derivatives of specific gene mutation, we analyzed the involvement of heat stress-responsive genes. Although the plasma is considered non-thermal, localized heating and the generated interactive stress is likely involved in the inactivation of E. coli bioaerosol. These findings provide a new dimension in underlying mechanisms of E. coli inactivation during DBD plasma exposure.Ph.D., Biomedical Engineering -- Drexel University, 201