The effects of 150 MPa and 500 MPa on germination of B. cereus spores were investigated. At low pressure (150 MPa), the germination and inactivation of wild-type spores increased with a rise in temperature from 20 to 65°C. Seven mutant spores were obtained, which were gerI, gerL, gerP, gerQ, gerT, gerN and gerTN. Each single mutant spore was eliminated particular proteins playing roles in the germination process. In general, various mutant spores behaved similarly to wild-type spores in most types of treatments. However, at 40°C, for pressure treatment at 150 MPa, gerL mutant spores exhibited 1.5-log more germination than wild-type spores in Tris buffer, and about 3-log more germination with addition of L-alanine. Germination by gerTN mutant spores was 1 to 2 logs lower than that of wild-type, gerT and gerN spores at 30 and 40°C in L-alanine, but these four strains of spores behaved similarly at 65°C.

At 500 MPa and 40°C, the gerL mutant spores had a 2-log higher germination than wild-type spores in inosine, while the gerI mutant spores behaved similarly to wild-type spores in all three buffers. At 50°C, the germination of wild-type, gerI and gerL spores were very similar. At 40°C, 150 MPa treatment gave better spore inactivation (1 to 2 logs) than 500 MPa for all types of spores. However, at 50°C, the low pressure (150 MPa) and very high pressure (500 MPa) treatments had very similar effects in germination and inactivation.

Milk provided good protection to spores under low and high pressure effects. In milk, gerI spores exhibited 2 logs higher germination at 150 MPa than at 500 MPa, while no significant difference in germination were observed between gerL and wild-type spores. At a pressure of 150 MPa, inactivation was more than 1 log higher than at 500 MPa for all three types of spores in milk.