The synergistic bactericidal mechanism of simultaneous treatment with a 222-nanometer krypton-chlorine excilamp and a 254- nanometer low-pressure mercury lamp

Abstract

The purpose of this study was to investigate the synergistic bactericidal effect of 222-nm KrCl excilamp and 254-nm low-pressure (LP) Hg lamp simultaneous treatment against Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium, and Listeria monocytogenes in tap water and to identify the synergistic bactericidal mechanism. Sterilized tap water inoculated with pathogens was treated individually or simultaneously with a 254-nm LP Hg lamp or 222-nm KrCl excilamp. Overall, for all pathogens, an additional reduction was found compared to the sum of the log unit reductions of the individual treatments resulting from synergy in the simultaneous treatment with both kinds of lamps. In order to identify the mechanism of this synergistic bactericidal action, the form and cause of membrane damage were analyzed. Total reactive oxygen species (ROS) and superoxide generation as well as the activity of ROS defense enzymes then were measured, and the overall mechanism was described as follows. When the 222-nm KrCl excilamp and the 254-nm LP Hg lamp were treated simultaneously, inactivation of ROS defense enzymes by the 222-nm KrCl excilamp induced additional ROS generation following exposure to 254-nm LP Hg lamp (synergistic) generation, resulting in synergistic lipid peroxidation in the cell membrane. As a result, there was a synergistic increase in cell membrane permeability leading to a synergistic bactericidal effect. This identification of the fundamental mechanism of the combined disinfection system of the 222-nm KrCl excilamp and 254-nm LP Hg lamp, which exhibited a synergistic bactericidal effect, can provide important baseline data for further related studies or industrial applications in the future.