Ingo Maier and Timothy Chu
The biocidal efficacy of ozone has been investigated in cryostats at -20°C and +30°C and 30-120 min exposure time. Stainless steel coupons were inoculated with 50 μl bacterial or viral test suspension. The tests were performed using Staphylococcus aureus and Mycobacterium terrae as test bacteria and Polyoma virus (Simian virus 40, SV 40). The inoculated coupons were exposed to a combination of ozone and UV generated by UV lamps in the cryostats. To measure the level of disinfection achieved, the number of surviving bacteria recovered from the coupons and, respectively, the virus infectivity titer was determined. Reduction factors were calculated by dividing the initial titer by the titer of recovered viable bacteria or virus.
Bactericidal efficacy at -20°C was demonstrated by inactivation of S. aureus by at least 5 log10 units in an automatic defrost/60 min ozone cycle in all test positions, which allowed to remove the +30°C/120 min test from the testing panel. In a 30 min treatment, a disinfection rate of 5 log10 units was achieved in some, but not all test positions. Mycobacterium terrae, the substitute for the pathogenic M. tuberculosis, was inactivated by >5.3 log10 units in all tested locations using a 120-minute ozone cycle at +30°C. The infective virus titer was reduced by at least 5 log10 units in the same ozone cycle on the pressure plate and chuck positions. Apart from this, significant reductions in viable cell and virus numbers have been shown for all disinfection protocols and test positions, thus demonstrating the principle efficacy of a combination of gaseous ozone and UV as a disinfectant in cryostats.
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