Influence of relative humidity on particle size and UV sensitivity of Serratia marcescens and Mycobacterium bovis BCG aerosols.
METHODS
A study of Serratia marcescens and BCG aerosols.


OBJECTIVE
To evaluate the effect of relative humidity (RH) on (1) the particle size and (2) sensitivity of 254nm germicidal ultraviolet (UV) irradiation.


METHODS
We built a RH controlled experimental chamber into which bacteria were aerosolized, exposed to varying amounts of UV irradiance over measured time periods, and quantitatively evaluated for viability. Aerosolized Serratia marcescens and bacille Calmette-Guérin (BCG) were subject to UV doses ranging from 57-829 microW. sec/cm(2), and sampled with a six-stage Andersen culture plate impactor at RHs ranging from 25-95%.


RESULTS
Percent survival for both organisms was inversely related to UV dose. Serratia marcescens was more susceptible to UV than BCG under all conditions. More than 95% of the bacterial aerosol particles were 1.1-4.7 microm in aerodynamic diameter, and particles sizes increased from low (25-36%) to high (85-95%) RH. The count median diameter ranged from 1.9-2.6 microm for Serratia marcescens and from 2.2-2.7 microm for BCG as RH increased. For both Serratia marcescens and BCG, resistance to UV increased as RH increased. The UV resistance of both Serratia marcescens and BCG aerosols dramatically increased at RH higher than 85%.


CONCLUSIONS
Our results indicate that differences in UV dose, kinds of microorganisms, airborne particle size and RH affect UV susceptibility.
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Department of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA.  
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D000336:Aerosols; D000818:Animals; D004307:Dose-Response Relationship, Radiation; D006813:Humidity; D009163:Mycobacterium bovis / Q000528:radiation effects*; D010316:Particle Size; D011836:Radiation Tolerance; D012706:Serratia marcescens / Q000528:radiation effects*; D014466:Ultraviolet Rays
D000336:Aerosols