Viricidal Efficacy of a 405‐nm Environmental Decontamination System for Inactivation of Bacteriophage Phi6: Surrogate for SARS‐CoV‐2

Abstract

The highly transmittable nature of SARS-CoV-2 has increased the necessity for novel strategies to safely decontaminate public areas. This study investigates the efficacy of a low irradiance 405-nm light environmental decontamination system for the inactivation of bacteriophage phi6 as a surrogate for SARS-CoV-2. Bacteriophage phi6 was exposed to increasing doses of low irradiance (~0.5 mW cm À2 ) 405nm light while suspended in SM buffer and artificial human saliva at low (~10 3-4 PFU mL À1 ) and high (~10 7-8 PFU mL À1 ) seeding densities, to determine system efficacy for SARS-CoV-2 inactivation and establish the influence of biologically relevant suspension media on viral susceptibility. Complete/near-complete (≥99.4%) inactivation was demonstrated in all cases, with significantly enhanced reductions observed in biologically relevant media (P < 0.05). Doses of 43.2 and 172.8 J cm À2 were required to achieve ~3 log 10 reductions at low density, and 97.2 and 259.2 J cm À2 achieved ~6 log 10 reductions at high density, in saliva and SM buffer, respectively: 2.6-4 times less dose was required when suspended in saliva compared to SM buffer. Comparative exposure to higher irradiance (~50 mW cm À2 ) 405-nm light indicated that, on a per unit dose basis, 0.5 mW cm À2 treatments were capable of achieving up to 5.8 greater log 10 reductions with up to 28-fold greater germicidal efficiency than that of 50 mW cm À2 treatments. These findings establish the efficacy of low irradiance 405-nm light systems for inactivation of a SARS-CoV-2 surrogate and demonstrate the significant enhancement in susceptibility when suspended in saliva, which is a major vector in COVID-19 transmission.

Enhanced antimicrobial efficacy and energy efficiency of low irradiance 405-nm light for bacterial decontamination

“…The concept that differences in inactivation efficacy may become increasingly evident when comparing irradiance applications of greater orders of magnitude is further supported by Endarko et al, who found no significant difference (P > 0.05) in the 405-nm light inactivation rate of L. monocytogenes when exposed to a constant dose using irradiances ranging from 44 to 85.6 mWcm −2 but did demonstrate significantly greater inactivation when exposed to a constant dose using 8.6 mWcm −2 in comparison to 85.6 mWcm −2 (Endarko et al 2012 ). More recently, Sinclair et al successfully inactivated bacteriophage phi6, as a surrogate for SARS-CoV-2, using a 405-nm light EDS at irradiances similar to that employed in this study (0.5 mWcm −2 ) and demonstrated up to 5.8 times greater log 10 reductions with up to 28-fold greater GE using this light source in comparison to a higher 50 mWcm −2 light source (Sinclair et al 2023b ). Although the results of this study cannot be directly compared with a viral surrogate, it is of interest to note that the enhancement in inactivation demonstrated here is likely apparent for a broad-spectrum of microbial species.…”

“…Exposure to these wavelengths induces the photoexcitation of endogenous porphyrin molecules within microbial cells, and a cascade of cellular processes resulting in the localised production of reactive oxygen species causing oxidative damage and cell death (Hamblin et al 2005 ; Maclean et al 2008 ). Although less germicidal than UV-light, the technology is inherently antimicrobial, and can achieve this at exposure levels compatible with mammalian cells (Ramakrishnan et al 2014 ; Tomb et al 2018 ), and because of this, there has been interest in its development for infection control applications which involve human exposure or treatment of sensitive materials, such as environmental decontamination applications (Maclean et al 2010 ; 2013 ; Bache et al 2012 , 2018 ; Murrell et al 2019 ; Sinclair et al 2023a , b ) or wound treatment (McDonald et al 2011 ; Dai et al 2013a , b ).…”