Heat resistance of Clostridium perfringens vegetative cells as affected byprior heat shock

This study quantified the heat resistance and the effects of a heat shock o n the subsequent heat resistance of 10 strains of Clostridium perfringens. Beef gravy samples inoculated with vegetative cells of the pathogen were su bjected to sublethal heating at 48C for 10 min, and then heated to a final temperature of 58C using a submerged-coil heating apparatus. Heat-treated s amples were spiral plated on Shahidi-Ferguson Perfringens agar to determine surviving bacterial population. No correlation between the heat resistance and the origin of the C. perfringens could be established due to significa nt variations in the hear resistance among strains. inactivation kinetics o f both heat-shocked and nonheat-shocked samples exhibited log-linear declin e in the number of surviving cells with time. D-values at 58C for C. perfri ngens vegetative cells ranged from 1.21 to 1.60 min. Heat shocking allowed the organism to survive longer and the increase in heat resistance tvas as high as 1.5 fold. Also, heat shock resulted in the overexpression of protei ns exhibiting epitopic and size similarity to E. coli GroEL and B. subtilis small acid soluble proteins. Increased heat resistance due to heat shock m ust be considered while designing cooking/reheating regimes that ensure saf ety of ready-to-eat foods contaminated with high numbers of C. perfringens vegetative cells.