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An investigation into the inhibitory effect of ultraviolet radiation on Trichophyton rubrum
Leah J Cronin1, Richard P Mildren, Michelle Moffitt
1School of Science and Health, University of Western Sydney, Campbelltown, NSW, 2560, Australia.
Abstract:
Fungal infection of nails, onychomycosis, is predominantly caused by Trichophyton rubrum. This infection is an important public health concern due to its persistent nature and high recurrence rates. Alternative treatments are urgently required. One such alternative is phototherapy involving the action of photothermal or photochemical processes. The aim of this novel study was to assess which wavelengths within the ultraviolet (UV) spectrum were inhibitory and equally important nail transmissible. Initial irradiations of T. rubrum spore suspensions were carried out using a tunable wavelength lamp system (fluence ≤3.1 J/cm(2)) at wavelengths between 280 and 400 nm (UVC to UVA) to evaluate which wavelengths prevented fungal growth. Light-emitting diodes (LEDs) of defined wavelengths were subsequently chosen with a view to evaluate and potentially implement this technology as a low-cost "in-home" treatment. Our experiments demonstrated that exposure at 280 nm using an LED with a fluence as low as 0.5 J/cm(2) was inhibitory, i.e., no growth following a 2-week incubation (p < 0.05; one-way ANOVA), while exposure to longer wavelengths was not. A key requirement for the use of phototherapy in the treatment of onychomycosis is that it must be nail transmissible. Our results indicate that the treatment with UVC is not feasible given that there is no overlap between the antifungal activity observed at 280 nm and transmission through the nail plate. However, a potential indirect application of this technology could be the decontamination of reservoirs of infection such as the shoes of infected individuals, thus preventing reinfection.
Insights
Phototherapy using 280 nm ultraviolet light inhibited fungal growth causing onychomycosis (nail fungus). However, this wavelength is not transmitted through nails, limiting direct treatment but offering potential for shoe decontamination to prevent reinfection.
Area of Science:
- Dermatology
- Photomedicine
- Mycology
Background:
- Onychomycosis, a persistent fungal nail infection primarily caused by Trichophyton rubrum, poses a significant public health challenge due to high recurrence rates.
- Current treatment options for onychomycosis are limited, necessitating the exploration of alternative therapeutic modalities.
- Phototherapy, utilizing photothermal or photochemical effects, presents a potential alternative treatment strategy for fungal nail infections.
Purpose of the Study:
- To investigate the efficacy of specific ultraviolet (UV) wavelengths in inhibiting the growth of Trichophyton rubrum.
- To determine the nail transmissibility of UV wavelengths exhibiting antifungal activity.
- To assess the potential of UV-based phototherapy as a novel treatment for onychomycosis.
Main Methods:
- In vitro irradiation of T. rubrum spore suspensions using a tunable wavelength lamp system (280-400 nm).
- Evaluation of fungal growth inhibition at various UV wavelengths and fluences (≤3.1 J/cm(2)).
- Subsequent experiments using light-emitting diodes (LEDs) of specific wavelengths to assess potential for low-cost home treatment.
Main Results:
- UV irradiation at 280 nm demonstrated significant inhibition of T. rubrum growth at a low fluence of 0.5 J/cm(2) (p < 0.05).
- Longer UV wavelengths (UVA) did not show significant antifungal activity.
- Crucially, the 280 nm wavelength exhibited poor nail plate transmission, precluding direct phototherapy for onychomycosis.
Conclusions:
- While 280 nm UV light is effective in inhibiting T. rubrum in vitro, its lack of nail transmissibility makes it unsuitable for direct onychomycosis treatment.
- The study suggests a potential indirect application for UV phototherapy in decontaminating environmental reservoirs, such as footwear, to prevent reinfection.
- Further research into optimizing UV delivery or exploring alternative wavelengths may be warranted for direct nail treatment.
