Increased thermotolerance of Clostridium perfringens spores following sublethal heat shock Vijay K. Juneja a, * , John S. Novak a , Lihan Huang a , Brian S. Eblen b a US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA 1 b Food and Drug Administration, Center for Food Safety and Applied Nutrition, 200 C. Street SW, Washington, DC 20250, USA Received 24 March 2002; accepted 27 May 2002 Abstract Beef gravy samples inoculated with Clostridium perfringens spores were heat shocked at 75 °C for 20 min, and then thermo- tolerance at 100 °C was assessed using a submerged-coil heating apparatus. Survivors were enumerated on Shahidi Ferguson Perfringens agar. An association of the heat resistance with the origin of the C. perfringens could not be established due to significant variations in the heat resistance among strains. Interestingly, deviations from classical logarithmic linear declines in the log numbers with time were not observed in both control and heat shocked samples. D-values at 100 °C for C. perfringens spores ranged from 15.5 to 21.4 min. Heat shocked spores of 9 out of 10 strains had significantly higher (p < 0:05) D-values at 100 °C than unstressed spores. Proteins with epitopic and size similarity to Escherichia coli GroEL and Bacillus subtilis small acid-soluble protein, SspC, were present in spores. However, heat shock treated spores did not appear to significantly increase expression of these proteins. Acquired thermotolerance is of substantial practical importance to food processors and should provide useful information for designing thermal treatments to eliminate C. perfringens spores in ready-to-eat foods. Published by Elsevier Science Ltd. Keywords: Clostridium perfringens; Heat resistance; Thermotolerance; Heat shock 1. Introduction Clostridium perfringens type A is an anaerobic, gram- positive, spore-forming, rod-shaped, non-motile bacte- rium. The organism continues to remain a major cause of foodborne illness and a concern to the food service industry world wide. It has been implicated in 248,520 cases of foodborne illnesses every year in the United States with 41 hospitalizations and seven deaths (Mead et al., 1999). In 1994, the total cost of illnesses due to C. perfringens was estimated at $123 million in the US (Anonymous, 1995). The food poisoning results from the ingestion of a large number of viable vegetative cells of the organism in temperature-abused foods. The heat labile enterotoxin synthesized by sporulating cells in the small intestine is responsible for the pathological effects in humans as well as the typical symptoms of diarrhea and abdominal pain. C. perfringens is found in soil, water, air, intestinal tract, and a variety of raw and processed foods, par- ticularly meat and poultry. Because of the ubiquitous distribution, it is difficult if not impossible to exclude spores of this pathogen during the processing of various animal or plant products and its presence must be as- sumed. Therefore, the thermal treatment applied to processed foods must be adequate to destroy the spores or their germination, outgrowth and subsequent vege- tative growth must be restricted, if the food is to be safe. Heat treatment designed to achieve a specific lethality for foodborne pathogens is a critical control point in food processing and is fundamentally important to as- sure the shelf-life and microbiological safety of ther- mally processed foods. A key to optimization of the heating step is defining the target pathogenÕs heat re- sistance. The heat resistance of any given microorganism is known to be affected not only by inherent ge- netic factors, but also by the environmental factors * Corresponding author. Tel.: +1-215-233-6500; fax: +1-215-233- 6559. E-mail address: vjuneja@arserrc.gov (V.K. Juneja). 1 Mention of brand or firm name does not constitute an endorse- ment by the US Department of Agriculture above others of a similar nature not mentioned. 0956-7135/02/$ - see front matter Published by Elsevier Science Ltd. PII:S0956-7135(02)00060-9 Food Control 14 (2003) 163–168 www.elsevier.com/locate/foodcont