Evaluation of Pressurized Steam Disinfection of Surfaces Contaminated by Mycobacterium terrae : A Surrogate for Mycobacterium bovis

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Introduction: Decontamination of farms affected by bovine tuberculosis could be very challenging during outbreaks occurring in the winter with freezing temperatures. Steam treatment has been of practical interest, but information is needed on whether such treatment is able to inactivate the causative agent, Mycobacterium bovis . This study was to evaluate the use of pressurized steam for inactivation of Mycobacterium terrae , a surrogate for M. bovis on various surfaces. Methods: Carrier disks made of steel, wood, or rubber were inoculated with 6.32 ± 0.38 log 10 M. terrae . While being held at background temperatures of −20°C, 4°C, or 21°C, these carrier disks were treated with pressurized steam (120°C ± 5°C) for 5, 10, 15, or 20 s. Reduction in colony forming units of M. terrae and temperatures on the top and bottom surfaces of the disks were determined. Results: Complete inactivation of 6 log 10 M. terrae on steel and wood disks was achieved by 10 s of steam treatment at all three background temperatures. In comparison, 20 s of steam treatment was needed for the complete inactivation of mycobacteria on rubber disks. Corresponding to the longer treatment time required for mycobacterial inactivation, temperatures on the bottom surface of the rubber disks rose substantially slower than those of the steel and wood disks at all three background temperatures. Conclusion: The results suggested that treatment with pressurized steam has potential for efficient and effective disinfection of surfaces contaminated by mycobacteria at or below freezing temperatures in winter.

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