Purpose: A study was initiated to validate the efficacy of chlorine dioxide gas (CD) on the inactivation of Listeria monocytogenes at low concentration levels and in short periods of time.
Methods: Traditional exposure for CD to achieve a 6-log sporicidal kill is 720 ppm-hours. Glass coupons inoculated with Listeria monocytogenes were introduced into a 17 cubic foot chamber and exposed to 50 – 720 ppm-hour decontamination cycles at 1 mg/l. The inoculated and exposed coupons were then enumerated and/or enriched along with proper controls to determine the total log reduction. Concentrations can be monitored in real time with a UV –VIS spectrophotometer to guarantee the correct exposure was achieved throughout the target area.
Results: Chlorine dioxide gas achieved greater than a 5-log reduction with a 400 ppm-hours exposure on glass coupons. A case study involving a 20,000 ft3 spiral freezer that was contaminated with Listeria spp. was successfully decontaminated using chlorine dioxide gas resulting in no positive swabs for up to 6 weeks after exposure.
Significance: Spiral freezers are very difficult to clean and therefore make it hard to prevent microbial contamination. Traditional methods for cleaning spiral freezers (i.e., spraying, foaming and wiping) are not completely effective because they are liquid-based methods and have difficulty getting everywhere. Filling the space with a sterilant gas and achieving complete coverage results in a more effective decontamination.