Photodynamic therapy in the antifungal treatment against systemic infection by Candida albicans in a model of Galleria mellonella

Objective: To investigate the efficacy of Antimicrobial Photodynamic Therapy (PDT) in combating infection by biofilm and planktonic cells of C. albicans in the in vivo model of Galleria mellonella. Methods: The inoculum was prepared at a concentration of 2x108 of C. albicans ATCC 90028 and clinical isolate A2 from planktonic cells and was also used for the preparation of biofilms. The larvae were inoculated with the aspirated content of the biofilms and with planktonic cell concentrations. They were then treated with antifungals, antimicrobial photodynamic therapy and red laser light. The laser energy used corresponded to a dose of 15 J/cm2 with a wavelength of 650nm and a power of 100 mW continuously, for 2 minutes and 30 seconds. The treatments were analyzed for 120 hours. At the end of the survival assays, 3 random larvae from each group were lysed, diluted in series and plated in selective medium for quantification of fungal load. Results: PDT and fluconazole showed the best results in the survival curve and in the decrease in fungal viability observed by the quantification of CFU/ml of C. albicans. Treatments with red laser light did not impact on longer survival or reduction of CFU/ml concentration. Conclusion: PDT has action against planktonic cells and biofilms of C. albicans compared to standard treatment with fluconazole. The red laser light alone did not show positive results, indicating that the red laser light alone did not show antimicrobial results.