Comparative Sensitivity of Trichophyton and Aspergillus Conidia to Inactivation by Violet-Blue Light Exposure.

OBJECTIVE: To investigate the use of 405 nm light for inhibiting the growth of selected species of dermatophytic and saprophytic fungi. BACKGROUND DATA: The increasing incidence and resilience of dermatophytic fungal infections is a major issue, and alternative treatment methods are being sought. METHODS: 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. RESULTS: Germination of the microconidia of the Trichophyton species was completely inhibited using an irradiance of 35 mW/cm(2) for 4 h (dose of 504 J/cm(2)). 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/cm(2) resulted in complete inactivation of T. rubrum microconidia, whereas A. niger showed greater resistance, and at the highest dose level applied (1440 J/cm(2)) although A niger hyphae were completely inactivated, only a 3-log10 reduction of a 5-log10 conidial suspension was achieved. CONCLUSIONS: 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.

Synergistic efficacy of 405 nm light and chlorinated disinfectants for the enhanced decontamination of Clostridium difficile spores.

The ability of Clostridium difficile to form highly resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is being developed for environmental decontamination within hospitals, however further information relating to its sporicidal efficacy is required. This study aims to establish the efficacy of 405 nm light for inactivation of C. difficile vegetative cells and spores, and to establish whether spore susceptibility can be enhanced by the combined use of 405 nm light with low concentration chlorinated disinfectants. Vegetative cells and spore suspensions were exposed to increasing doses of 405 nm light (at 70-225 mW/cm(2)) to establish sensitivity. A 99.9% reduction in vegetative cell population was demonstrated with a dose of 252 J/cm(2), however spores demonstrated higher resilience, with a 10-fold increase in required dose. Exposures were repeated with spores suspended in the hospital disinfectants sodium hypochlorite, Actichlor and Tristel at non-lethal concentrations (0.1%, 0.001% and 0.0001%, respectively). Enhanced sporicidal activity was achieved when spores were exposed to 405 nm light in the presence of the disinfectants, with a 99.9% reduction achieved following exposure to 33% less light dose than required when exposed to 405 nm light alone. In conclusion, C. difficile vegetative cells and spores can be successfully inactivated using 405 nm light, the sporicidal efficacy can be significantly enhanced when exposed in the presence of low concentration chlorinated disinfectants. Further research may lead to the potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures.