Efeito da terapia fotodinâmica antimicrobiana mediada por butil azul de toluidina O (BuTBO) em candida albicans

Abstract

Candida albicans is one of the most common fungal infections in humans, acting both as part of the normal microbiota and as an opportunistic pathogen. It colonizes sites such as the skin, mouth, gastrointestinal tract, and vagina. In healthy individuals, it is detected in saliva and oral mucosa in approximately 40% of cases and is associated with periodontal disease. Moreover, infection by C. albicans can trigger Th17-mediated inflammation, highlighting the need for effective and long-lasting treatments. Antimicrobial Photodynamic Therapy (aPDT) is a promising approach that uses photosensitizers activated by light to inhibit or kill microorganisms. This study investigated the antimicrobial effect of aPDT mediated by Toluidine Blue O Butyl (BuTBO) on C. albicans. Using the C. albicans ATCC 90028 strain, yeast cells were cultured on Sabouraud Dextrose Agar, and the efficacy of BuTBO was evaluated in comparison with control groups. The results demonstrated that irradiation without a photosensitizer was not effective against C. albicans (p > 0.05). From 2 minutes of irradiation onward, a reduction in microbial load was observed, with a large number of cells inactivated after 2 minutes. Fluorescence microscopy revealed that BuTBO predominantly localized inside the yeast cells, with the photosensitizer accumulating intracellularly at an order of 1012 molecules per cell. The data suggest that irradiation time is a critical factor for the activation of the photosensitizer and the generation of reactive oxygen species (ROS), which are essential for cellular inactivation. aPDT with BuTBO demonstrated high efficacy against C. albicans, starting the death of the fungus after 2 min of irradiation. The combination of the photosensitizer with light is crucial for ROS production, which drives the antimicrobial effect. Longer irradiation times (3 and 5 minutes) were found to be key determinants of treatment success. BuTBO accumulates within fungal cells and generates ROS without disrupting cellular structure, making it a promising candidate for controlling fungal infections.