Evaluation of the Effects of Photodynamic Therapy With Methylene Blue on Different Candida Species In Vitro

Introduction: Oral candidiasis is the most prevalent opportunistic infection of the oral cavity. The most common cause of this infection is Candida albicans. Considering the side effects of conventional antifungal therapies, this study aimed to evaluate the efficacy of photodynamic therapy with new methylene blue (a photosensitizer) in inhibiting the growth of C. albicans, C. tropicalis, C. glabrata, and C. krusei in vitro. Methods: In this experimental study, 200 samples of standard suspension (0.5 McFarland) were prepared from C. albicans, C. tropicalis, C. glabrata, and C. krusei (50 samples from each species). The samples of each species were divided into five groups (n=10), including photodynamic therapy with a photosensitizer, with or without laser irradiation, nystatin treatment, laser therapy, and control. Next, cultivation of samples was performed on Sabouraud dextrose agar, and the colony-forming units were determined after 24 hours of incubation at 37 °C. Data were analyzed in SPSS version 22 by means of the Kruskal-Wallis test (P<0.05). Results: The most sensitive and resistant species to nystatin therapy were C. glabrata and C. krusei, respectively. On the other hand, C. krusei was the most sensitive species to photodynamic therapy, and C. glabrata was the most resistant type to this treatment. The highest therapeutic effectiveness was attributed to nystatin therapy, although photodynamic therapy was also effective. Laser therapy was recognized as the least effective method. Conclusion: Photodynamic therapy with new methylene blue, as a suitable adjunct therapy, can be effective in the management of candidiasis. It may also be a potential novel treatment for immunocompromised patients with oral candidiasis.