Susceptibility of Escherichia coli O157:H7 grown at low temperatures to the krypton-chlorine excilamp

This study was conducted to investigate the resistance of Escherichia coli O157:H7 to 222-nm krypton-chlorine(KrCl) excilamp and 254-nm low-pressure Hg lamp (LP lamp) treatment according to growth temperature. As growth temperature decreased, lag time of E. coli O157:H7 significantly increased while the growth rate significantly decreased. Regardless of growth temperature, the KrCl excilamp showed higher disinfection capacity compared to the LP lamp at stationary growth phase. KrCl excilamp treatment showed significantly higher reduction as growth temperature decreased. Conversely, reduction levels according to growth temperature were not significantly different when the pathogen was subjected to LP lamp treatment. Inactivation mechanisms were evaluated by the thiobarbituric acid reactive substances (TBARS) assay and SYBR green assay, and we confirmed that lipid oxdiation capacity following KrCl excilamp treatment increased as growth temperature decreased, which was significantly higher than that of LP lamp treated samples regardless of growth temperature. DNA damage level was significantly higher for LP Hg lamp treated samples compared to those subjected to the KrCl excilamp, but no significant difference pursuant to growth temperature was observed. At the transcriptional level, gene expression related to several metabolic pathways was significantly higher for the pathogen grown at 15 degrees C compared that of 37 degrees C, enabling it to adapt and survive at low temperature, and membrane lipid composition became altered to ensure membrane fluidity. Consequently, resistance of E. coli O157:H7 to the KrCl excilamp decreased as growth temperature decreased because the ratio of unsaturated fatty acid composition increased at low growth temperature resulting in higher lipid oxidation levels. These results indicate that KrCl excilamp treatment should be determined carefully considering the growth temperature of E. coli O157:H7.