High-intensity 405 nm light inactivation of Listeria monocytogenes

The antimicrobial properties of light is an area of increasing interest. This paper investigates the sensitivity of the significant foodborne pathogen Listeria monocytogenes to selected wavelengths of visible-light. Results demonstrate exposure to wavelengths region 400–450nm, at sufficiently high dose levels (750Jcm2), induced complete inactivation of a 5-log10 population. Exposure to wavelengths longer than 450nm did not cause significant inactivation. Analysis of 10nm bandwidths between 400 and 450nm confirmed 405(±5)nm light to be most effective for inactivation of L. monocytogenes, with a lesser bactericidal effect also evident at other wavelengths between 400 and 440nm. Identification of the optimum bactericidal wavelength enabled comparison of inactivation using 405(±5)nm filtered light and a 405nm LED array (14nm FWHM). Results demonstrate similar inactivation kinetics, indicating that the applied dose of 405-nm light is the important factor. Use of the 405nm LED array for inactivation of L. monocytogenes and other Listeria species resulted in similar kinetics, with up to 5-log10 reductions with a dose of 185Jcm2. Comparative data for the 405nm light inactivation of L. monocytogenes and other important foodborne pathogens, Escherichia coli, Salmonella enteritidis and Shigella sonnei, is also presented, with L. monocytogenes showing higher susceptibility to inactivation through 405nm light exposure