Microbial air sampling based on elecrostatic precipitation
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Bioaerosol exposure assessment and the protection of civil/governmental/military establishments from bioterrorism require the development of low-power bioaerosol collectors that are able not only to efficiently collect airborne microorganisms, but also to preserve their biological integrity. In search for such a method, a new bioaerosol sampler was evaluated. In this device, the airborne microorganisms are imparted electrical charges and are then deposited in an electrical field onto a growth medium (agar). Experiments were conducted with Pseudomonas fluorescens vegetative cells, Bacillus subtilis var. niger (BG) endospores (used to simulate the spores of anthrax-causing Bacillus anthracis when testing bioaerosol sensors) and Penicillium brevicompactum fungal spores. It was found that 80–90% of initially “charge-neutralized” biological particles were removed from the air, when a small amount of ionization was generated in the electrostatic precipitator's (ESP) inlet and a precipitation voltage of was applied across the agar plates. Over 70% of viable BG and P. brevicompactum spores entering the ESP were enumerated as colony forming units. The bioefficiency of the new sampler was about the same as that of the Biosampler, which was tested in parallel. In experiments with sensitive P. fluorescens vegetative cells, the ESP enumerated twice as many cells as the Biosampler. The latter result indicates that the electrostatic collection method may be especially useful for the collection and enumeration of sensitive airborne microorganisms. Experiments investigating the effect of aging time on the amount of electrical charge carried by the airborne microorganisms showed that the level of electrical charge gradually decreases with increasing aging time. However, even after the P. fluorescens cells had remained airborne for an hour, they retained enough electrical charge to be collected with efficiency higher than 70%.