Sporulation temperature affects initiation of germination and inactivation by high hydrostatic pressure of Bacillus cereus

The influence of sporulation temperature (20, 30 and 37 degrees C) on the heat resistance and initiation of germination and inactivation by high pressure on Bacillus cereus ATCC 14579 spores was investigated. Spores sporulated at 37 degrees C were the most heat-resistant. However, spores sporulated at 20 degrees C were more resistant to the initiation of germination and inactivation by high pressure. Spores were more sensitive to pressure at higher treatment temperatures. At 25 degrees C, there was an optimum pressure (250 MPa) for the initiation of germination for the three suspensions; at higher temperatures an increase of pressure up to 690 MPa caused progressively more germination. Resistance to the germinability and inactivation by high pressure of the spore population was distributed heterogeneously. Semilogarithmic curves of the ungerminated and survival fraction of B. cereus spores were concave. The resistant fraction of the spore population was lower at higher treatment temperatures. At 60 degrees C after 30 s of treatment at 690 MPa almost 5 log cycles of the population of B. cereus sporulated at 20 degrees C was germinated, and more than 7 log cycles of the population of B. cereus sporulated at 30 and 37 degrees C. The same treatment inactivated 4, 6 and 7 log cycles of the population of B. cereus sporulated at 20, 30 and 37 degrees C, respectively.