Heat-induced temperature sensitivity of outgrowing Bacillus cereus spores

Abstract

Inactivation of Bacillus cereus spores during cooling (10°C/h) from 90°C occurred in two phases. One phase occurred during cooling from 90 to 80°C; the second occurred during cooling from 46 to 38° C. In contrast, no inactivation occurred when spores were cooled from a maximum temperature of 80°C. Inactivation of spores at a constant temperature of 45°C was induced by initial heat treatments from 80 to 90°C. The higher temperatures accelerated the rate of inactivation. Germination of spores was required for 45°C inactivation to occur; however, faster germination was not the cause of accelerated inactivation of spores receiving higher initial heat treatments. Repair of possible injury was not observed in Trypticase soy broth (BBL Microbiology Systems), peptone, beef extract, starch, or L-alanine at 30 or 35° C. Microscopic evaluation of spores outgrowing at 45°C revealed that when inactivation occurred, outgrowth halted at the swelling stage. Inhibition of protein synthesis by chloramphenicol at the optimum temperature also stopped outgrowth at swelling; thus protein synthesis may play a role in the 45°C inactivation mechanism.