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Journal Article 
The synergistic bactericidal mechanism of simultaneous 222-nm krypton-chlorine excilamp and 254-nm low-pressure mercury lamp treatment 
Kang, JW; Kang, DH 
Applied and Environmental Microbiology
ISSN: 0099-2240
EISSN: 1098-5336 
The purpose of this study was to investigate the synergistic bactericidal effect of 222-nm KrCl excilamp and 254-nm 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 was analyzed, and then total ROS and superoxide generation and activity of ROS defense enzymes 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 induced additional ROS generation following exposure to the 254-nm (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 application studies or industrial applications in the future.IMPORTANCE Contamination of pathogenic microorganisms in water plays an important role in inducing outbreaks of foodborne illness by causing cross contamination in foods. Thus, proper disinfection of water before use in food production is essential to prevent outbreaks of foodborne illness. As technologies capable of selecting UV radiation wavelengths (such as UV-LEDs and Excilamps) have been developed, research efforts on wavelength combination treatment with UV radiation, which is widely used in water disinfection systems, are actively being studied. In this regard, we have confirmed synergistic bactericidal effects in combination with 222-nm and 254-nm wavelengths and have identified mechanisms for this. This study clearly analyzed the mechanism of synergistic bactericidal effect by wavelength combination treatment and it has not been attempt in other studies. Therefore, it is also expected that these results will play an important role as baseline data for future research investigations on the disinfection strategy of effective wavelength combinations as well as industrial applications. 
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