STUDIES ON FACTORS AFFECTING THE HEAT RESISTANCE OF SPORES OF CLOSTRIDIUM BOTULINUM

Abstract

The heat resistance of C. botulinum spores grown under varying cultural conditions was studied. Some effects of different treatments of the formed spores on their heat resistance were investigated. Spores formed at 37[degree] C are of higher heat resistance than those developed at 41, 29. or 24[degree]C. Below a certain concn., the lower the Fe++ and Ca concn. of the sporulating medium the lower is the thermostability of the spores. Addition of Ca++ and Mg++ to the spore-suspending menstruum, reduces the heat tolerance of the spores. Fatty acids in the sporulating medium influence the heat tolerance of the spores. In general, it appears that the longer the fatty acid chain, the greater is the increase in thermal tolerance. The excess fatty acid salts must be removed from the spore suspension to unmask the true resistance from the apparent resistance which results from the suppression of the germination of the heated but still viable spores by the higher fatty acids. The degree of unsaturation of the C18 fatty acids shows some correlation with the heat lability of the spores. Chloroform or petroleum ether extraction of the sporulating medium (casitone broth) results in spores of diminished thermal tolerance. Serum albumin added in sufficient concn. neutralizes the effect of the fatty acids. The thermal resistance of spores suspended in different concns. of sucrose increases with the concn. of the sucrose. With spores suspended in 50% sucrose the increase in heat resistance is almost immediate and remains high for many hrs. Spore suspensions of C. botulinum can be divided into 2 fractions of different heat stabilities by separating the spores of the sediment from the supernatant spores of young, unshaken broth cultures.