Relationship between the heat resistance of spores and the optimum and maximum growth temperatures of Bacillus species

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Abstract
Heat resistance of spores of Bacillus strains was compared with the temperature adaptation of each strain as measured by the optimum and maximum growth temperatures and the heat resistance of vegetative cells. Maximum growth temperatures ranged from 31-76.degree. C and were little affected by the nature of the growth medium. The temperature giving maximum growth rate was closely correlated to the maximum temperature for growth, and about 6.degree. C lower. Vegetative-cell heat resistance, determined on exponential-phase cells, was also correlated with maximum growth temperature. The temperature at which spores were inactivated with a decimal reduction time of 10 min was in the range of 75-121.degree. C. This temperature was 46 .+-. 7.degree. C higher than the maximum growth temperature and correlated with it and the other cell parameters. Spore heat resistance can be considered to have 2 components, the temperature adaptation characteristic of the species and the stabilization conferred by the spore state.