Comparison of PDT using a 660 nm laser and methylene blue vs. an 810 nm laser and indocyanine green on different Candida species – in vitro

Abstract

Introduction: Photodynamic therapy (PDT) offers broad-spectrum antifungal effects with lower resistance in some studies. This study evaluates the effectiveness of two PDT protocols, using a 660 nm diode laser with methylene blue (MB) compared to an 810 nm diode laser with indocyanine green (ICG), in reducing colony counts of Candida albicans, C. glabrata, C. tropicalis, and C. krusei. Methods: This experimental laboratory study tested 4 standard Candida species in seven groups (2 PDT, 2 photosensitizers alone, 2 lasers wavelength with saline, 1 control with saline) each containing five replicates per species. PDT was performed using MB with a 660 nm diode laser and ICG with an 810 nm diode laser. Laser exposure setting was 100 mW, 10 J/cm², 100 s. CFUs were quantified, and statistical analysis was performed using SPSS version 26, with significance set at P < 0.05. Results: PDT had better efficacy for colony count reduction of C. tropicalis, and C. krusei. PDT with an 810 nm diode laser and ICG had better efficacy than PDT with 660 nm diode laser and MB but difference was not significant (P > 0.05). For some candida species there was no significant difference between PDT with laser alone for colony reduction but there was significant difference between them with each photosensitizer and saline alone (P < 0.05). Conclusion: Both PDT had better efficacy for colony count reduction of C. tropicalis, and C. krusei compare to other two species. PDT with diode 810 nm and ICG seems better than PDT with diode 660 nm and MB, but the difference was not statistical between two methods. © The Author(s) 2026.