Heat and Radiation Resistance and Activation of Spores of Clostridium welchii

SUMMARY Spores of‘classical’strains of Clostridium welchii were more sensitive to heat ( D 90° 3–5 min) than spores of‘food poisoning’strains ( D 90° 15–145 min) from the same sporulation media. The z values of‘classical’strains ( z =11–14°F) were lower than for‘food poisoning’strains ( z = 16–29°F). 30–50% of spores of‘classical’strains grew without heating, and no heat activation was detected. Only 0.13‐3.6% of spores of‘food poisoning’strains grew without heating, heat activation being generally detected at 75–80°, and on one occasion at 75–100°. Spores of‘food poisoning’strains were more resistant to γ radiation ( D =0.26‐0.34 Mrad) than spores of‘classical’strains ( D =0.12‐0.21 Mrad).