HEAT-RESISTANCE OF SPORES OF NONPROTEOLYTIC CLOSTRIDIUM-BOTULINUM ESTIMATED ON MEDIUM CONTAINING LYSOZYME

Heat treatment of spores of non-proteolytic strains of Clostridium botulinum at 75-90-degrees-C and enumeration of survivors on a nutrient medium containing lysozyme gave biphasic survival curves. A majority of spores were inactivated rapidly by heating, and the apparent heat-resistance of these spores was similar to that observed by enumeration on medium without lysozyme. A minority of spores showed much greater heat-resistance, due to the fact that the spore coat was permeable to lysozyme, which diffused into the spore from the medium and replaced the heat-inactivated germination system. The proportion of heated spores permeable to lysozyme was between 0.2 and 1.4% for spores of strains 17B (type B) and Beluga (type E), but was about 20% for spores of strain Foster B96 (type E). After treatment of heated spores with alkaline thioglycolate, all were permeable to lysozyme. D-values for heated spores that were permeable to lysozyme (naturally and after treatment with thioglycolate) were: for strain 17B, D85-degrees-C, 100 min; D90-degrees-C, 18.7 min; D95-degrees-C, 4.4 min; for strain Beluga, D85-degrees-C, 46 min; D90-degrees-C, 11.8 min; D95-degrees-C, 2.8 min. The z-values for these spores of strains 17B and Beluga were 7.6-degrees-C and 8.3-degrees-C.