Purpose Lighting systems which use visible light blended with antimicrobial 405-nm violet-blue light have recently been developed for safe continuous decontamination of occupied healthcare environments. This paper characterises the optical output and antibacterial efficacy of a low irradiance 405-nm light system designed for environmental decontamination applications, under controlled laboratory conditions. Methods In the current study, the irradiance output of a ceiling-mounted 405-nm light source was profiled within a 3×3×2 m (18 m3) test area; with values ranging from 0.001-2.016 mWcm-2. To evaluate antibacterial efficacy of the light source for environmental surface decontamination, irradiance levels within this range (0.021-1 mWcm-2) at various angular ($$\Delta$$ Δ ϴ=0-51.3) and linear (∆s=1.6-2.56 m) displacements from the source were used to generate inactivation kinetics, using the model organism, Staphylococcus aureus. Additionally, twelve bacterial species were surface-seeded and light-exposed at a fixed displacement below the source (1.5 m; 0.5 mWcm-2) to demonstrate broad-spectrum efficacy at heights typical of high touch surfaces within occupied settings. Results Results demonstrate that significant (P≤0.05) inactivation was successfully achieved at all irradiance values investigated, with spatial positioning from the source affecting inactivation, with greater times required for inactivation as irradiance decreased. Complete/near-complete (≥93.28%) inactivation of all bacteria was achieved following exposure to 0.5 mWcm-2 within exposure times realistic of those utilised practically for whole-room decontamination (2-16 h). Conclusion This study provides fundamental evidence of the efficacy, and energy efficiency, of low irradiance 405-nm light for bacterial inactivation within a controlled laboratory setting, further justifying its benefits for practical infection control applications.
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.
Background: Pathogen reduction technologies (PRT) for blood products can reduce the incidence of transfusion-transmitted infection and associated wastage of blood products. Visible 405nm-light has been shown to inactivate bacteria in situ in bagged blood plasma without the addition of photo-sensitive chemicals. However, threshold levels for plasma protein compatibility and optimal bactericidal activity are currently unknown. This study investigates different treatment conditions and their suitability for safely inactivating bacteria in blood plasma. Method: Plasma seeded with Staphylococcus aureus (102–105CFU/ml) was exposed to 405nm-light at low and high irradiances (10, 100mW/cm2) with treatment times ranging between 0.2–7-hr (≤252 Jcm-2). SDS-PAGE was then used to assess the light effect in terms of antimicrobial treatment levels on plasma protein integrity. Results: High and low intensity treatment regimens achieved significant bacterial inactivation (P=<0.05) with doses of 252 Jcm-2 achieving ≥99.3% reduction. Results suggest that lower irradiances have greater germicidal efficiency, with use of 10mWcm-2 achieving up to 30% greater inactivation than equivalent doses using 100mWcm-2. SDS-PAGE analysis demonstrated no major detrimental impact on protein integrity with any of the treatment conditions investigated. Minimal changes in protein bands (≈28kDa) were observed relative to positive control samples after application of doses >144 Jcm-2. Conclusion: The results of this study have highlighted the safety potential of 405nm-light treatment on blood plasma. Further research is required to determine the upper and lower threshold treatment levels and functionality of plasma proteins post-exposure for further development of this technology as a PRT tool for application in transfusion medicine.
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