Thermal inactivation of spores of Bacillus atrophaeus, Bacillus anthracis, Bacillus cereus, and Clostridium difficile

Abstract

There are inadequate evidence on the sporicidal effect of hot water. Therefore, we evaluated the efficacy of hot water against spores of Bacillus atrophaeus, Bacillus anthracis, Bacillus cereus, and Clostridium difficile. A portion (0.05 ml) of the spore suspension was used to inoculate 4.95 ml of sterilized distilled hot water. After standing for 1, 2, 5, 10, 30, and 60 min, 0.5 ml was added to 4.5 ml of physiological saline at room temperature (20°C–22°C). The spores of B. atrophaeus were the most resistant to hot water, followed by those of B. anthracis, B. cereus, and C. difficile. Disinfection of spores using hot water required contact at 100°C for 30 min for B. atrophaeus and B. anthracis, at 90°C for 30 min or at 100°C for 5 min for B. cereus, and at 90°C for 10 min or at 100°C for 2 min for C. difficile. All tested spores cannot be killed under the general conditions of use of hot-water washing machines (70°C–80°C, 10 min), but the spores of C. difficile can be killed under the general conditions of use of washer disinfectors (90°C–93°C, 10 min).