Comparing the Antibacterial Effects of 660 nm Laser Therapy on <i>Staphylococcus aureus</i> Using Phycocyanin and Methylene Blue: An In-Vitro Study

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Background: Staphylococcus aureus is a leading cause of oral and nasopharyngeal infections, with antibiotic-resistant strains posing significant health challenges. Photodynamic therapy (PDT) is a recommended alternative antimicrobial treatment. Objectives: This study aimed to evaluate and compare the antibacterial effects of 660 nm laser irradiation in combination with phycocyanin and methylene blue (MB) on S. aureus colonies. Methods: In this in vitro study, the effects of 660 nm laser irradiation (100 mW for 100 s) were analyzed on S. aureus colonies using varying concentrations of phycocyanin (0.00001 to 0.005 mg/mL) and MB (0.00001 to 0.02 mg/mL). Data were analyzed using the two-way random block design test. Results: The results demonstrated that laser irradiation combined with MB at concentrations of 0.005 and 0.002 mg/mL significantly reduced the number of S. aureus colonies compared to other treatments (P-value < 0.01). Methylene blue without PDT was effective in destroying all colonies at concentrations ≥ 0.01 mg/mL. Laser irradiation combined with MB at concentrations of 0.001, 0.0005, and 0.0002 mg/ml, or with phycocyanin at concentrations of 0.02, 0.01, and 0.005 mg/mL, reduced the number of colonies. However, laser irradiation alone, laser combined with phycocyanin at concentrations ≤ 0.002 mg/mL, or laser combined with MB at concentrations ≤ 0.0001 mg/mL, did not significantly reduce colony numbers (P-value > 0.05). Conclusions: This study demonstrated that MB combined with laser irradiation was more effective in eliminating S. aureus. The findings suggest that adding photosensitizing agents enhances the antibacterial effects of laser irradiation.