Effect of water-surface discharge on the inactivation of Bacillus Subtilis due to protein lysis and DNA damage

Abstract

The effect of water-surface discharge on the inactiva- tion of Bacillus subtilis ATCC6633 in water was examined by using a very short high-voltage pulse generator. The surviving number of spore cells at 104 CFU/ml in initial concentration exponentially decreased with increasing discharge-treatment time. The input energy into the water-surface discharge under an O2 gas flow for reduction in the survival number to 10% was lower than that under an air flow because many oxidation agents such as ozone and OH radical were produced under the O2 gas flow. The input energy density for the one-tenth reduction depended not only on the spore state but also on the initial cell concentration. The input energy for the high- concentration spore cells (107 CFU/ml) was much higher than that for the low-concentration spore cells (104 CFU/ml). Cellular proteins and DNA were degraded by a 30-min discharge treatment of vegetative cells, whereas DNA of the high-concentration spore cells was relatively resistant.