The Mode and Kinetics of Death of the Bacterial Spores by Moist Heat

In order to find out the mechanism of death of bacterial spores by heat, several experiments were carried out using the three aerobic strains, Bacillus natto, Bacillus megatherium, and Bacillus mycoides.When the spores of these strains were heated in M/15 phosphate buffer (pH 7.0), the relationships between the initial spore cencentration (N spores per ml) and the survival time (ts) were found to be expressed by the following equation: log N=a+b log ts This linear relationship between log N and log ts was confirmed to exist in general, though the values of the constants a and b varied with many factors such as heating temperature, heating menstrum, strain, and the kind of subculture medium.When the spores of Bac natto were subcultured in glucose broth (nutrient broth plus 0.5% glucose) the survival time of the spores was twice as much as that obtained in plain nutrient broth. The minimum effective concentration of glucose in increasing the survival time of the spores was found to lie between 10-5M and 10-6M, and the same order of glucose concentration has limited the growth of the spores in a synthetic medium. The other sugars, such as fructose, mannose, galactose, sucrose, maltose, starch, pyruvate, and alpha- glycerophosphate were also effective in elongating the survival time when they were added to nutrient broth in which the heated spores of Bac. natto were subcultured. All these effective sugars were also effective in supporting good growth of Bac. natto spores in the synthetic medium.The effects of vitamins and amino acids in the subculture medium on the survival times of Bac. natto. spores were then studied using a complete synthetic medium. Though the spores of Bac. natto require only biotin for their growth the presence of thiamine and pyridoxal in the subculture medium in addition to biotin was effective in elongating the survival time of the spores.When each of various amino acids was added to the synthetic subculture medium as a sole source of nitrogen, the survival time of Bac. natto spores varied markedly with the kind of the added amino acid. The order of the length of the survival time obtained with each amino acid was as follows:leucine<lysine<histidine and proline<arginine and aspartic acid