Application of KrCl excilamp for surface disinfection of foodborne pathogen

Abstract

This study was conducted to investigate the basic spectral properties of 222-nm krypton-chlorine (KrCl) excilamp and its inactivation efficacy against major foodborne pathogens on solid media, as well as on sliced cheese compared to conventional 254-nm low-pressure Hg (LP Hg) lamp. The KrCl excilamp showed full radiant intensity from the outset at a wide range of working temperatures, especially at low temperature around 0 to 10 °C. Selective media and sliced cheese inoculated with Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes were irradiated with a KrCl excilamp and a LP Hg lamp at the same dose. Irradiation with 222-nm UV-C showed significantly (P < 0.05) higher inactivation capacity against all three pathogens than 254-nm radiation on both of media and sliced cheese surfaces without generating many sublethally injured cells which potentially could recover. The underlying inactivation mechanisms of the 222-nm KrCl excilamp treatment were evaluated by fluorescent staining methods and damage to cellular membranes and intracellular enzyme inactivation were the primary factors contributing to the enhanced bactericidal effect. And this study was also conducted investigate the resistance of Escherichia coli O157:H7 to 222-nm KrCl excilamp and 254-nm LP Hg lamp treatment according to growth temperature. As growth temperature decreased, lag time of E. coli O157:H7 IV significantly increased while the growth rate significantly decreased. Regardless of growth temperature the KrCl excilamp showed higher disinfection capacity compared to the LP Hg 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 Hg lamp treatment. Inactivation mechanisms were evaluated by the thiobarbituric acid reactive substances (TBARS) assay and SYBR green assay, and confirmed that lipid oxidation capacity following KrCl excilamp treatment increased as growth temperature decreased, which was significantly higher than that of LP Hg 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. 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. The results of this study suggest that a 222-nm UV-C surface disinfecting system can be applied as an alternative to conventional LP Hg lamp in the surface disinfection