Thermochemical Factors Influencing the Death Kinetics of Spores of Clostridium botulinum 62 A

SUMMARY: Death kinetics of spores of Clostridium botulinum, Type A, strain 62, were studied at sterilant gas temperatures in the range of 40°C (104°F) to 70°C (158°F). Hygroscopic carriers in the form of small discs of filter paper were used. The sterilant gas used was a mixture of dichlorodifluoromethane and ethylene oxide (88 and 12% by weight respectively). Pressures in the exposure atmosphere were adjusted to obtain an ethylene oxide concentration of 700 mg per liter at all temperatures. It was shown by gas-chromatographic analysis that an actual concentration of 700 ± 20 mg per liter was maintained at all exposure temperatures during all exposure periods. The effect of various moisture levels on spore death kinetics was also studied. The relative humidities employed in both the preconditioning and exposure of spores were 3, 23, 33, 53 and 73%, respectively. Thermochemical resistance parameters, D and z, were calculated as the reciprocals of the slopes of the survivor curves and thermochemical destruction time curves, respectively. Of the various environmental moisture levels studied, a preconditioning and exposure relative humidity of 3% for destruction of C. botulinum spores taken from an aqueous suspension, was found to be most effective. This effect held for all temperatures studied. Over the range studied, temperature was seen to have the greatest effect at 3% relative humidity (RH), second greatest at 33% and least effect at 73%.