Antimicrobial effect of photodynamic therapy using erythrosine/methylene blue combination on Streptococcus mutans biofilm

Background: Photodynamic therapy (PDT) has demonstrated promising results in the treatment of several clinical pathologies through the photochemical reaction caused by the combination of a photosensitizer and a light source. The objective of this study was to evaluate the antimicrobial effect of the combination of the photosensitizers (PSs) erythrosine/methylene blue activated by a white halogen light device on Streptococcus mutans biofilm. Methods: Two separate experiments were conducted, the first using the PSs at the concentration of 100 mu M, and the second 250 mu M. The PSs were tested on S. mutans biofilms cultured for 24 h in isolation, in combination, with and without light activation for 2 min fractionated in 4 periods of 30 s. After treatment, biofilms were diluted and plated on BHI medium and incubated for 24 h for colony forming units (CFU) counting. The results (log(10)) were analyzed with ANOVA followed by Tukey test (p < 0.05). Results: The erythrosine/methylene blue combination activated by white halogen light at 100 and 250 mu M, and erythrosine at 250 mu M, methylene blue at 250 mu M presented significantly reduced cell counts (3.2 log(10), 5.3 log(10), 4.5 log(10), 4.3 log(10), respectively) when compared to controls (p < 0.05). Conclusion: PDT with the combination of erythrosine/methylene blue demonstrated better results that the PSs in isolation regardless of the concentration. The use of this combination at the concentration of 250 mu M shows promise as an antibacterial treatment for carious lesions and should be further assessed.