Comparison of viability and heat resistance of Clostridium sporogenes stored at different temperatures.

The objective of this study was to determine the influence of storage temperature on the viability and heat resistance of Clostridium sporogenes spores. Spore suspension containing both spores and vegetative cells was divided into 3 groups to be stored at different temperatures of -20 (freezing), 4 (refrigerating), and 25 degrees C (ambient temperature). Samples stored for different times within the 2 mo were tested for viability by comparison of colony counts on plates and for heat resistance by determining D values at 121 degrees C. No significant differences were found in the viability of vegetative cells during the storage period, regardless of storage temperatures tested, while the viability of the spores stored for more than 4 wk was significantly higher at 4 degrees C than at -20 degrees C. The heat resistance of spores stored at 4 degrees C for more than 4 wk was remarkably higher than that at 25 degrees C, but similar to that at -20 degrees C throughout the storage period. Consequently, it turned out that a refrigerating temperature of 4 degrees C is satisfactory for storage of C. sporogenes spores in maintaining viability and heat resistance. This study suggests that storage temperature influences the viability and heat resistance of C. sporogenes spores.