Potassium iodide enhances inactivation of Streptococcus mutans biofilm in antimicrobial photodynamic therapy with red laser

Objective: To evaluate the effect of potassium iodide (KI) addition on antimicrobial photodynamic therapy (aPDT) mediated by red laser (lambda = 660 nm) and methylene blue in Streptococcus mutans biofilm model. Methods: S. mutans biofilms were cultured in 96-well plates containing BHI broth with 1% sucrose for 18 h, 10% CO2 and 37 degrees C and divided in groups (n = 3, in triplicate): C (NaCl 0.9%); CX (0.2% chlorhexidine); P (photosensitizer); KI (10, 25 and 50 mM); PKI (10, 25 and 50 mM); L (L1: 100 J/cm(2), 9 J; L2: 200 J/cm(2), 18 J); PL (photosensitizer + L1 or L2); KIL (KI at 10, 25 and 50 mM + L1 or L2); and PKIL (photosensitizer + 10, 25 and 50 mM KI + L1 or L2). Biofilms were submitted to three pre-irradiation (PI) times (5, 10, and 15 min). After the treatments, microbial counting's reduction was analyzed by Kruskal-Wallis and post-hoc Dunn's tests, respectively, and the interaction between light parameters and the PI times by two-way ANOVA (p < 0.05). Results: The S. mutans viability significantly reduced in all aPDT groups, in the presence or absence of KI (p < 0.05). For all PI times, PKIL groups (10, 25, and 50 mM) significantly differed from PL groups (p < 0.05) with a reduction of 9.0 logs reached at 50 mM of KI with 15 min of PI, irradiated at 18 J. We found no significant interaction between PI time and irradiation (p > 0.05). Conclusion: The addition of KI to PDT mediated by methylene blue and red laser promoted an additional effect in reducing the microbial viability of S. mutans biofilm.