Variability in Heat Resistance of Sporeformers; How Diverse is Diversity?

Realistic prediction of microbial inactivation in food requires quantitative information on variability introduced by the microorganisms. Bacillus species form heat- resistant spores and variability in spore heat resistance varies among species. Therefore, the spore heat resistance of the spoilage organisms Bacillus subtilis and Geobacillus stearothermophilis, and the foodborne pathogen Bacillus cereus were characterized in detail using twenty strains per species. This allowed comparison of variability in spore heat resistance between and within Bacillus species. In addition, reproduction variability was determined using two biologically independent spore crops for each strain which were heat treated on different days. Reproduction variability was significantly lower than strain variability for all three species. A meta-analysis on spore heat resistance of Bacillusspecies demonstrated that strain variability explained at least 50% of all variability in heat resistance of sporeformers. This indicates that integration of microbiological variability in prediction makes predictions not more accurate, yet more realistic.