Pressure, temperature impact inactivation and germination of B. cereus spores.

The goal of scientists at the University of Delaware was to study the germination and inactivation of B. cereus spores exposed to hydrostatic pressure and elevated temperature.

Investigators determined the extent of inactivation by the number of survivors plated on nutrient agar directly after pressure treatment. Germination was determined by viable counts after the pressure-treated spores were exposed to 70 C for 10 minutes.

For B. cereus 569, the wild-type strain, 15-minute treatments at 37 C resulted in: a 3.9 [log.sub.10] germination after exposure to 150 MPa; a 3.2 [log.sub.10] germination at 200 MPa exposure; and a 3.0 log[10.sub.10] germination after exposure at 250 MPa using an initial spore count of ~1 x 108 per mL.

Spore inactivation from 15 minute treatments at 37 C reached: 3.0 [log.sub.10] at 150 MPa; 1.9 [log.sub.10] at 200 MPa; and 1.3 [log.sub.10] at 250 MPa. Exposure to pressures of 150 MPa resulted in higher levels of germination and inactivation than exposure to pressures ranging from 200 MPa to 250 MPa at 37 C. Exposure to 150 MPa and 30 C for 15 minutes yielded a 2.1 [log.sub.10] germination and a 1.0 [log.sub.10] inactivation.

Similar experiments with germination mutants, gerI5 and gerL1, which lacked inosine and L-alanine receptors, respectively, demonstrated: 2.0 [log.sub.10] germination; 1.6 [log.sub.10] inactivation (gerI5); 3.1 [log.sub.10] germination; and 1.7 [log.sub.10] inactivation (gerL1). The treatment conditions were 150 MPa at 37 C for 15 min.

These data suggest that low pressures of approximately 150 MPa triggered the germination of B. cereus spores, and germinant receptors--gerI5 and gerL1--played a role in the mechanism of germination induced by high pressure and elevated temperatures. Other germination mutants, such as gerP (which lacked inosine receptors) and gerN (which lacked germinant-transfer proteins), were also deficient in pressure-induced germination. They appeared to possess a similar germination mechanism. Temperature also played an important role in spore inactivation. High pressure and elevated temperatures of 50 C to 65 C increased the rate of germination.

Further information. Dallas Hoover, Department of Animal and Food Sciences, University of Delaware, 017 Townsend Hall, 531 S. College Ave., Newark, DE 19716; phone: [phone]; fax: [phone]; email: [e-mail].