Investigating the Effect of Photodynamic Therapy With a 660 nm Laser With Methylene Blue and Cold Atmospheric Plasma Therapy on <i>Streptococcus sanguinis</i>

<b>Introduction:</b> This study was conducted to investigate the effect of photodynamic therapy (PDT) with a 660 nm laser along with methylene blue (MB) and cold atmospheric plasma therapy (CAP) on <i>Streptococcus sanguinis</i>. Since <i>S. sanguinis</i> plays a pivotal role in biofilm formation, alongside its ability to survive in the bloodstream, it significantly heightens the risk of infective endocarditis. <b>Methods:</b> In this in-vitro study, the <i>S. sanguinis</i> strain was cultured on a blood agar medium, and the samples were evenly distributed among eight experimental groups using equalization methods with nine repetitions. The experimental groups were 8 groups. Following the interventions, the samples were cultured using the pour plate method. After 48 hours, the samples were retrieved, and the number of bacterial colonies was counted. The changes in colony numbers, after normal transformation, were analyzed using the repeated measures ANOVA model, with the between-subject factor considered in the analysis. <b>Results:</b> The highest colony count was observed in the control group. Particularly, in both the PLASMA group and the group treated with PLASMA+PDT using the 660 nm laser alone, there was no significant difference from the control group (PLASMA: <i>P</i>>0.05; PLASMA+PDT: <i>P</i>>0.05). However, the combination of CAP, PDT with the 660 nm laser, and MB demonstrated a significant reduction in colony counts compared to the control group (PLASMA+PDT+MB: <i>P</i>=0.000), making it the most effective intervention in this study. <b>Conclusion:</b> The results demonstrated that the combination of CAP and PDT using a 660 nm laser with MB achieved the most significant reduction in <i>S. sanguinis</i> colonies.