Violet-Blue Light Arrays at 405nm Exert Enhanced Antimicrobial Activity for Photodisinfection of Monomicrobial Nosocomial Related Biofilms

Light-emitting diodes (LEDs) demonstrate therapeutic effects for a range of biomedical applications including photodisinfection. Specific wavelength bands (centred at 405nm) are reported to be the most antimicrobial, however there remains no consensus on most effective irradiation parameters for optimal photodisinfection. The aim of this study was to assess decontamination efficiency by direct photodisinfection of monomicrobial biofilms using single (SWA), and multi wavelength (MWA) violet-blue light (VBL) arrays. Mature biofilms of nosocomial bacteria (Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) were grown on 96 well polypropylene PCR plates. The biofilms were then exposed to VBL for 2700 seconds (SWA) and 1170s (MWA), to deliver 0-670J/cm2 and the antibacterial activity of VBL assessed by comparing the seeding of the irradiated and non-irradiated biofilms. Non -irradiated groups were used as controls. VBL arrays were characterised optically (spectral irradiance and beam profile), and thermally. The SWA delivered 401nm VBL and the MWA delivered between 379 nm and 452nm albeit at different irradiances and beam profiles. In both arrays, irradiated groups were exposed to increased temperatures compared to non-irradiated controls. All bacterial isolates were susceptible to VBL and demonstrated reductions in seeding of exposed biofilms compared with non-irradiated controls. VBL at 405nm exerted the most antimicrobial activity, exhibiting reductions in seeding of up to 94%. Decontamination efficiency is dependent on irradiation parameters, bacterial species and strain, and experimental conditions. Controlled experiments that ameliorate heating effects and improve optical properties are required to optimise dosing parameters to advance successful clinical translation of this technology. Importance This study reports the efficacy of VBL and BL, and its antimicrobial activity against mature biofilms of a range of important nosocomial pathogens. Whilst this study investigates the antibacterial activity of a range of wavelengths between 375-450nm, and identifies a specific wavelength region (∼405nm) with increased antibacterial activity, decontamination was dependent on bacterial species, strain, irradiation parameters and experimental conditions. Further research with controlled experiments that ameliorate heating effects, and improve optical properties are required to optimise dosing parameters to advance successful clinical translation of this technology.