Degradation of aerosolized bacterial spores from ultraviolet radiation

Abstract

The most accurate insight to how aerosolized material responds to UV radiation is obtained by performing experiments on freely suspended particles, absent from the shadowing that deposition on a surface may impose. For this purpose we have developed a linear electrodynamic particle trap to confine suspended particles using a contact-free technique. The trap allows us to challenge and study aerosols under controlled environmental parameters such as temperature, humidity and radiation exposure. We present the results of a quantitative study on the changes in viability of Bacillus anthracis Sterne strain spores confined within this trap and illuminated by either simulated sunlight or a UV light source at 253.7 nm. Up to 500 same-size particles, (that is, consisting of approximately the same number of spores), were created from a dropleton-demand injector, trapped and irradiated with varying time scales. Illumination times ranged from 5 to 300 seconds with a maximum fluence of 500 J/m2 using the UV source, and particle clusters containing as little as 1 up to as many as 55 spores were used. As will be discussed, the viability of spores decreased as total fluence increased as expected, and for the same fluence, viability improved as the number of spores in each particle increased.