Treatment of oral candidiasis with methylene blue-mediated photodynamic therapy in an immunodeficient murine model

Objective. The purpose of this study was to evaluate the efficacy of using methylene blue (MB)-mediated photodynamic therapy to treat oral candidiasis in an immunosuppressed murine model, mimicking what is found in human patients. Study design. Seventy-five experimental mice with severe combined immunodeficiency disease were inoculated orally with Candida albicans by swab 3 times a week for a 4-week period. On treatment day, mice were cultured for baseline fungal growth and received a topical oral cavity administration of 0.05 ml_ MB solution at one of the following concentrations: 250, 275, 300, 350, 400, 450, or 500 μg/mL After 10 minutes the mice were recultured and underwent light activation with 664 nm of diode laser light with a cylindrical diffuser. After photodynamic therapy the mice were cultured again for colony-forming units per milliliter and then killed, their tissue harvested for histopathology. Results and conclusions. The results indicate an MB dose-dependent effect. Concentrations from 250 to 400 μg/mL reduced fungal growth but did not eliminate Candida albicans. MB concentrations of 450 and 500 μg/mL totally eradicated Candida albicans from the oral cavity, resulting in reductions from 2.5 log₁₀ and 2.74 log₁₀ to 0, respectively. These results suggest that MB-mediated photodynamic therapy can potentially be used to treat oral candidiasis in immunodeficient patients.