The efficacy of photodynamic and photothermal therapy on biofilm formation of Streptococcus mutans: An in vitro study

Background: The alternative antibacterial treatments of photodynamic therapy (PDT) and photothermal therapy (PIT) significantly affect microbiota inactivation. The aim of the present research was the assessment of the antimicrobial and anti-biofilm effects of PDT with toluidine blue O (TBO) and PTT with indocyanine green (ICG) on Streptococcus mutans as a cariogenic bacterium. Materials and methods: The S. mutans ATCC 35668 strain was treated with final concentrations of 0.1 mg/mL TBO and 1 mg/mL ICG with energy densities of 17.18 and 15.62 J/cm(2), respectively. Cell viability was evaluated after culturing and anti-biofilm potential was analyzed using crystal violet assay and scanning electron microscopy. Results: The number of S. mutans colony forming unit (CFU)/mL was significantly lower in the groups submitted to PDT (12.5-100 mu g/mL TBO) and PTT(62.5-1000 mu g/mL) compared to the control (untreated group). 0.1 mg/mL TBO-PDT and 1 mg/mL ICG-PTT showed stronger inhibitory effects on biofilm formation in S. mutans than other concentration levels, with a reduction of 63.87% and 67.3%, respectively. Conclusion: Photo-elimination by high concentrations of TBO-PDT and ICG-PTT exhibited significantly stronger inhibitory effects on biofilm formation and cell viability in S. mutans. (C) 2016 Elsevier B.V. All rights reserved.