Evidence for Bacillus cereus Spores as the Target Pathogen in Thermally Processed Extended Shelf Life Refrigerated...

The microbial safety concern associated with thermally processed extended shelf life (ESL) refrigerated foods is based on adequate elimination of spore-forming pathogens such as nonproteolytic Clostridium botulinum types B, E, and F. These pathogens are traditionally regarded as targets for validation of thermally processed ESL foods. However, their use for research is restricted due to their designation as select agents. In this study, the thermal resistances of spores of 10 nonproteolytic C. botulinum types B and F and seven psychrotrophic Bacillus cereus strains were evaluated in ACES (N-(2-acetamido)-2-aminoethanesulfonic acid) buffer (0.05 M, pH 7.00) and compared to determine whether any of the B. cereus strains could serve as a nonselect agent for establishing thermal processes for ESL refrigerated foods. Thermal decimal reduction times (DT-values) of both nonproteolytic C. botulinum types B and F and psychrotrophic B. cereus strains decreased as process temperature increased from 80 to 91°C, and the highest values were obtained at 80°C. All psychrotrophic B. cereus strains tested were more thermally resistant than nonproteolytic C. botulinum types B and F. DT-values of nonproteolytic C. botulinum types B and F decreased to <1.0 min at 87°C, whereas all psychrotrophic B. cereus strains had higher DT-values (i.e., 52.35 to 133.69 min) at the same temperature. Among all psychrotrophic B. cereus strains tested, BC-6A16 had the highest DT-values at any given temperature. The DT-values indicated that the psychrotrophic B. cereus strains were more thermally resistant than the nonproteolytic C. botulinum strains and therefore may be potential target pathogens for thermal process validation of ESL refrigerated foods. However, further comparative challenge studies are needed with a model food system or an ESL refrigerated food to confirm these results.