Collection of Airborne Microorganisms by Electrostatic Precipitation

The applicability of electrostatic precipitation as a method for bioaerosol collection was investigated by using a modified Electrostatic Aerosol Sampler (EAS) (Model 3100, TSI Inc., St. Paul, MN). The physical and biological efficiencies of this method were determined. The tests were performed using three bacterial species which were collected onto agar, into water, and onto filters. The physical collection efficiency was higher than 80% when using a sampling flow rate of 1 L/min. When the Bacillus subtilis var niger (BG) spores were collected on agar, about 50-60% of the collected culturable organisms formed colonies. The bioefficiency exceeded 90% when the BG spores were collected on a filter, but was only 15-22% when collected into water. The Mycobacterium bovis BCG bacteria recovered at the 0-8% level on all three collection media. The least number of colonies were formed when Pseudomonas fluorescens bacteria were collected on any of the collection media. The data show that the process of electrostatic collection is very complex for sensitive airborne bacteria and thus several effects should be considered when assessing its bioefficiency. In separate tests conducted without aerosol flow through the sampler, bacteria placed onto the collection media did not show any significant reduction in bacterial recovery while exposed to a strong electric field. It was found that evaporation from the collection media, such as agar or water, increases the humidity inside the EAS and may affect the size distribution of the particles being collected, resulting in decreased physical and biological efficiencies of the electrostatic precipitation method. For hardy microorganisms such as BG spores, the bioefficiency for electrostatic collection is high, thus encouraging further explorations of the electrostatic method for sampling bioaerosols.