Inactivation of Bacillus subtilis spores by a combination of hydrostatic high-pressure and pulsed electric field treatments

The effect of the combination of hydrostatic high-pressure (HHP) and pulsed electric field (PEF) treatments on the inactivation of Bacillus subtilis spores was investigated, using suspensions prepared by suspending the spores in various solutions at about 10⁸ spores/ml. When the PEF and HHP treatments were successively conducted in that order, the results were compared with the case where either was conducted alone. The combined processing achieved a 7.1 log reduction in the viable spore counts at maximum. Low-temperature storage after the combined processing further led to reduced germination, and finally completes inactivation in 3 days. It was confirmed by phase-contrast microscopy that the non-treated spores gradually turned into phase-dark spores and finally germinated and changed into vegetative cells, while the spores subjected to PEF/HHP treatment did not transfer to the phase-dark stage, meaning no germination.