Antimicrobial 405 nm light for clinical decontamination : investigation of the antiviral efficacy and potential for bacterial tolerance

Tomb, Rachael Margaret

Thesis

Antimicrobial 405 nm light for clinical decontamination : investigation of the antiviral efficacy and potential for bacterial tolerance

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Creator

Tomb, Rachael Margaret.

Awarding institution

University of Strathclyde

Date of award

2017

Thesis identifier

T14730

Person Identifier (Local)

201372392

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Electronic and Electrical Engineering.

Abstract

Hospital associated infections result in longer patient stays, increased treatment costs and morbidity and mortality. Novel technologies utilising UV light, hydrogen peroxide vapour and ozone have been designed to provide high-level environmental decontamination, in an attempt to prevent patient acquisition of nosocomial pathogens. However due to safety concerns, these technologies are only suitable for intermittent terminal cleaning, and surfaces can become quickly re-contaminated. Recently developed systems which utilise antimicrobial 405 nm violet-blue visible light have been successfully used for continuous decontamination of surfaces and air, in the presence of patients. This study investigated some fundamental questions surrounding the use of antimicrobial 405 nm light for clinical decontamination.Initial investigations studied the antiviral efficacy of 405 nm light on a model for the nosocomial pathogen, Norovirus. Studies showed positive antiviral effects in suspension and on clinically-relevant surfaces when virions were exposed in minimal media (DPBS), however this inactivation efficacy was significantly improved (85% lower dose) when the virus was suspended in organically-rich, biologically-relevant media (such as saliva and blood plasma). This enhanced inactivation is likely due to photoexcitation of the suspending media, and was demonstrated using fluorescence spectrophotometry, with excitation peaks seen for all suspending media except minimal media. A systematised review also compared 405 nm light inactivation of viruses with other clinical pathogens (bacteria, fungi), and found that viruses (exposed in minimal media) are more resilient structures, requiring higher doses for equivalent reductions, likely due to differing inactivation mechanisms.Further studies also investigated the potential for proliferating and non-proliferating bacteria, Staphylococcus aureus, to become tolerant to 405 nm light. Results demonstrated that exposure to 405 nm light during cultivation resulted in higher dose requirements for complete inactivation and increased stress tolerance, however the process was unlikely to be selective. Results also demonstrated that repeated sub-lethal exposure of antibiotic sensitive and resistant vegetative cells did not give rise to tolerance or alter antibiotic susceptibility.This study has provided significant fundamental information about antimicrobial violet-blue light. The results demonstrate proof-of-concept evidence of the virucidal efficacy of 405 nm light, as well as demonstrating that bacterial tolerance is unlikely. These results further support the clinical use of antimicrobial 405 nm light for continuous environmental decontamination, with implementation likely to aid infection control and reduce hospital associated infections.

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