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The degree of heat resistance conferred on Clostridium perfringens by a heat shock, the kinetics of this development, and its duration were determined. A sublethal heat shock at 55°C for 30 min increased the heat tolerance of vegetative cells at least two- to threefold. The acquired tolerance was maintained for 2 h after the heat shock treatment. Heat shock applied for the first hour of incubation produced spores more tolerant to heat than the spores of the control. Acquired thermotolerance is of importance in the case of this organism because of its inherently high optimal growth temperature.

Several reports on the microbiology of spices and herbs indicate the presence of Clostridium perfringens, a spore-forming foodborne pathogen responsible for gastrointestinal disease. In the present study, a total of 380 samples of spices and herbs (cumin seed, black pepper, oregano, garlic powder, and bay leaves) widely used in Mexico were analyzed for the presence of C. perfringens, and the enterotoxigenicity of the isolates was determined by a dot-blot technique using an enterotoxin digoxigenin-labeled DNA probe. C. perfringens counts varied from <100 to 500 CFU/g in garlic powder, from <100 to 200 CFU/g in black pepper, from <100 to 433 CFU/g in cumin seed, from <100 to 340 CFU/g in oregano, and from <100 to 450 CFU/g in bay leaves. The dot-blot technique detected the enterotoxin gene in 8 (4.25%) of 188 confirmed isolates of C. perfringens. dot-blot

Application of a heat shock (43 to 50 degrees C) applied early during the sporulation process of Clostridium perfringens delayed spore and enterotoxin production. Final levels of heat-resistant spores were similar to the control, but enterotoxin levels were reduced when the heat shock was applied at the third hour of incubation. The response of the microorganism to the heat shock was also examined by analysis of pulse-labeled proteins. Seven heat shock proteins (HSPs) associated with vegetative cells were identified by polyacrylamide gel electrophoresis. Most were localized mainly in the membrane, although one small protein was mostly present in the cytoplasm. Fewer HSPs were detected during sporulation. Two HSPs were immunologically related to the GroEL and DnaK HSPs from Lactobacillus lactis and Escherichia coli, respectively.

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