Application of Gaseous Ozone for Inactivation of Bacillus subtilis Spores

Abstract

The effectiveness of gaseous ozone (O₃) as a disinfectant was tested on Bacillus subtilis spores, which share the same physiological characteristics as Bacillus anthracis spores that cause the anthrax disease. Spores dried on surfaces of different carrier material were exposed to O₃ gas in the range of 500–5000 ppm and at relative humidity (RH) of 70–95%. Gaseous O3 was found to be very effective against the B. subtilis spores, and at O₃ concentrations as low as 3 mg/L (1500 ppm), ∼3-log inactivation was obtained within 4 hr of exposure. The inactivation curves consisted of a short lag phase followed by an exponential decrease in the number of surviving spores. Prehydration of the bacterial spores has eliminated the initial lag phase. The inactivation rate increased with increasing O₃ concentration but not ∼3 mg/L. The inactivation rate also increased with increase in RH. Different survival curves were obtained for various surfaces used to carry spores. Inactivation rates of spores on glass, a vinyl floor tile, and office paper were nearly the same. Whereas cut pile carpet and hardwood flooring surfaces resulted in much lower inactivation rates, another type of carpet (loop pile) showed significant enhancement in the inactivation of the spores.