Germination and subsequent inactivation of bacillus subtilis spores by pulsed electric field treatment

The use of high-intensity pulsed electric field (PEF) as a nonthermal method for triggering spore germination was investigated. Spores suspended in 0.01% NaCl solution (ca. 10⁸cells/mL) were treated with an exponential-decay pulse (20-50 kV/cm) at selected temperatures. The inactivation resulting from the direct effect of PEF treatment was less than 0.5 log cycles, even with a relatively high electric field intensity of 40 kV/cm. Most of the surviving PEF-treated spores germinated after inoculation into selected germination media (0.85% NaCl solution, nutrient broth [NB], or tryptic soy broth [TSB]) and subsequent incubation at 37C for 40 min. The extent of germination increased with the treatment temperature and electric field intensity. More than 98% of surviving spores in TSB germinated during incubation after PEF treatment with an electric field strength of 40 kV/cm for 1,000 μs at 50C. The rate of germination in nutrient-rich TSB medium was higher than that in NB.