Comparative Analysis of the Photodynamic Effects of Phycocyanin and Methylene Blue on <i>Rhizopus oryzae</i>: An in vitro Study

Abstract

Background: Mucormycosis is a severe invasive fungal infection primarily caused by Rhizopus oryzae, particularly in immunocompromised individuals, including patients with diabetes or those receiving steroid therapy. Globally, mucormycosis is among the most frequently reported opportunistic invasive fungal infections, after candidiasis and aspergillosis. Treatment is challenging because of frequent resistance to standard antifungal therapies, necessitating combined surgical and pharmacological interventions. Recent advances have investigated photodynamic therapy (PDT) as an alternative or adjunctive treatment for fungal infections. Objectives: This study aimed to compare the efficacy of PDT using two photosensitizers, phycocyanin (PC) and methylene blue (MB), against Rhizopus oryzae. Methods: In this experimental study, Rhizopus oryzae was cultured on Sabouraud dextrose agar. PC and MB were used as photosensitizers with a 660-nm laser at varying power settings (100 mW and 200 mW) and exposure times (125, 250, 500, and 1000 seconds), with the laser positioned at a distance of 1 cm from the suspension. After laser exposure, 100 µL of the treated suspension was re-cultured. Amphotericin B was used as a positive control. The treatment effect on colony-forming units/mL was analyzed using one-way analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) test in SPSS version 24. The level of significance was set at 0.05. Results: Amphotericin B exhibited superior antifungal activity compared with PDT. However, PDT using a 660-nm laser and PC demonstrated greater lethality against Rhizopus oryzae than the combination of a 660-nm laser and MB. Conclusions: Although amphotericin B remains more effective, PDT, particularly with PC, shows potential as an adjunct treatment for mucormycosis and warrants further investigation.