Comparative sensitivity of Trichophyton and Aspergillus conidia to inactivation by violet-blue light exposure

Moorhead, Sian and MacLean, Michelle and MacGregor, Scott J. and Anderson, John G. (2016) Comparative sensitivity of Trichophyton and Aspergillus conidia to inactivation by violet-blue light exposure. Photomedicine and Laser Surgery, 34 (1). pp. 36-41. ISSN 1557-8550 (https://doi.org/10.1089/pho.2015.3922)

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Abstract

The objective of this paper was to investigate the use of 405 nm light for inhibiting the growth of selected species of dermatophytic and saprophytic fungi. The increasing incidence and resilience of dermatophytic fungal infections is a major issue, and alternative treatment methods are being sought. The sensitivity of the dermatophytic fungi Trichophyton rubrum and Trichophyton mentagrophytes to 405 nm violet-blue light exposure was investigated, and the results compared with those obtained with the saprophytic fungus Aspergillus niger. Microconidia of T. rubrum and T. mentagrophytes and conidia of A. niger were seeded onto Sabauroud dextrose agar plates and irradiated with 405 nm light from an indium-gallium-nitride 99-DIE light-emitting diode (LED) array and the extent of inhibition was measured. Germination of the microconidia of the Trichophyton species was completely inhibited using an irradiance of 35 mW/cm2 for 4 h (dose of 504 J/cm2). Results: A. niger conidia showed greater resistance, and colonial growth developed after light exposure. In liquid suspension tests, 405 nm light dose levels of 360, 720, and 1440 J/cm2 resulted in complete inactivation of T. rubrum microconidia, whereas A. niger showed greater resistance, and at the highest dose level applied (1440 J/cm2 ) although A niger hyphae were completely inactivated, only a 3-log10 reduction of a 5-log10 conidial suspension was achieved. The study results demonstrate the relatively high sensitivity of Trichophyton microconidia to 405 nm violet-blue light, and this is may be of potential interest regarding the control and treatment of dermatophyte infections.

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