Group I Clostridium botulinum Strains Show Significant Variation in Growth at Low and High Temperatures

Abstract

The minimum and maximum growth temperatures of 23 group I Clostridium botulinum strains of the toxin types A, AB, B, and F were determined. Moreover, the maximum growth rates at 20, 37, and 42°C of the same strains were recorded. The minimum growth temperatures varied from 12.8 to 16.5°C, whereas the maximum growth temperatures showed even wider variation, from 40.9 to 48.0°C. At 20 and 37°C, a twofold difference in maximum growth rates between the slowest and the fastest growing strains was found; at 42°C the difference was more than 30-fold. As expected, all strains grew significantly slower at 20°C than at 37°C. However, eight type B strains grew substantially faster at 42°C than they did at 37°C. These findings indicate that the optimum growth temperature for some group I C. botulinum type B strains is higher than the temperature of 37°C that is generally accepted. A significant correlation between maximum growth rates at 42°C and maximum growth temperatures was found for type B and F strains, whereas for type A strains no such correlation could be found. Strain variation was particularly high for the type B strains, reflecting the wide genetic diversity of this toxin type. The significant variation between strains of group I C. botulinum may have an impact on inoculation studies and predictive modeling when assessing the safety of foods.