Antifungal effect of 5‐aminolevulinic acid PDT in Trichophyton rubrum

Summary In the present investigation, we have shown for the first time that the onychomycosis‐inducing dermatophyte Trichophyton rubrum was able to metabolize 5‐aminolevulinic acid (ALA) to protoporphyrin IX (PpIX) in liquid culture medium. We have established and optimized the culture conditions and could show the typical PpIX‐induced red fluorescence which was evaluated qualitatively by Wood's light examination and fluorescent microscopic analysis. The optimum concentration of ALA was in the range of 1–10 mmol l −1 . If used in higher concentrations, ALA leads to a significantly reduced growth rate and absence of PpIX formation due to highly acidic conditions. The first observation of red fluorescence was detected between 10 and 14 days poststimulation with ALA, increasing thereafter. Fluorescent microscopic examinations demonstrated that formation of PpIX was restricted to selected parts of the fungal mycelium. Repeated application of ALA in order to achieve the highest formation of PpIX in T. rubrum failed, probably due to the sustained low pH values. ALA treatment and irradiation of T. rubrum clearly demonstrated the growth‐inhibiting effect of ALA PDT, either leading to reduced numbers of colonies or reduced diameters of single fungal colonies. Summarizing our results, ALA PDT might be a promising approach in the reduction of T. rubrum colonization in onychomycosis.