Photodynamic therapy of Candida biofilms

Objectives: Photodynamic therapy (PDT) utilizes light to activate a photosensitizing agent (photosensitizer) in the presence of oxygen. The exposure of the photosensitizer to light results in the formation of toxic oxygen species, causing localized photo-damage and cell death. Candida-associated denture stomatitis is a common recurrent disease in denture wearers. The formation of C. albicans biofilms contributes to the failure of antifungal therapy and to recurrent infections. In this study, the photodynamic activity of the porphyrin-based photosensitizer TMP-1363 towards Candida biofilms, formed on denture acrylic discs, was investigated in the absence and presence of the azole antifungal, miconazole.Methods: The effect of TMP-PDT ± miconazole on Candida biofilms was determined for four clinical isolates, C. albicans 6122/06, C. tropicalis 8122/06, C. parapsilosis 11375/06 and C. glabrata 7531/66. Biofilms were developed on poly(methyl methacrylate) discs. Candida biofilms were incubated with miconazole, followed by treatment with TMP-1363 (10 µg/ml) for 30 min at 37°C. The plates were exposed to broadband visible light (350-800 nm) from a light bulb at a distance of 10 cm from the light bulb to the plate, for 30 min. The irradiance at the surface of the plate was 32.5 mW/cm2. Infrared radiation was minimized using a 1 cm water filter. The metabolic activity of the biofilms was measured by the XTT assay.Results: The photodynamic activity of TMP-1363 alone towards Candida biofilms reduced metabolic activity of biofilms by ~35%, while miconazole alone reduced metabolic activity by ~37.5%. Combined treatment with miconazole + TMP-PDT was more effective, reducing metabolic activity by 55%, 73%, 68% and 50% for C. tropicalis, C. albicans, C. parapsilosis and C.glabrata biofilms, respectively. Treatment of Candida biofilms with TMP-1363 in the absence of light was not cytotoxic.Conclusion: Miconazole increased the sensitivity of Candida biofilms to the photodynamic activity of the porphyrin-based photosensitizer TMP-1363