Photodynamic Antimicrobial Chemotherapy (PACT), using Toluidine blue (TBO) inhibits both growth and dimorphism in Paracoccidioides brasiliensis by a mechanism involving reactive oxygen species (ROS) production

Background: The thermo-dimorphic fungus Paracoccidioides brasiliensis is the pathogen of Paracoccidioidomycosis, an important public health problem in Latin American with prevalence in Brazil. Photodynamic Antimicrobial Chemotherapy (PACT) is a process that combines a photosensitizer and light, producing reactive oxygen species (ROS) that can promote damages to treated cells. Methods: In this work was study the effect of PACT, using Toluidine blue (TBO) on both yeast and mycelial cells of P. brasiliensis. Results: It was observed that PACT decreased P. brasiliensis yeast growth, in a dependent manner of both TBO concentrations and fluence. In the presence of TBO 0.005 mg/mL, PACT reduced P. brasiliensis yeast growth in 63, 62 and 86%, using fluences of 20, 30 and 40 J/cm(2), respectively. After PACT, ROS production increased 2.80, 4.64 and 7.90 times, in the presence of TBO 0.001, 0.002 and 0.005 mg/mL, respectively. It was observed that after PACT, the cells are predominantly in mycelia form, indicating that mycelial cells irradiated in the presence of TBO, maintained their filamentous form and absence and/or decreased presence of transition structures. Conclusions: These results demonstrated the potential of PACT, using TBO to inhibit both yeast and mycelium development of P. brasiliensis.