Antimicrobial photodynamic therapy mediated by methylene blue coupled to β-cyclodextrin reduces early colonizing microorganisms from the oral biofilm

Abstract

Objective: To test the effect of antimicrobial photodynamic therapy (A-PDT) on the oral biofilm formed with early colonizing microorganisms, using the photosensitizer methylene blue coupled with β-cyclodextrin nanoparticles and red light sources laser or LED (λ =660 nm).

Methods: The groups were divided into (n = 3, in triplicate): C (negative control, 0.9 % NaCl), CX (positive control, 0.2 % chlorhexidine), P (Photosensitizer/Nanoparticle), L (Laser), LED (light-emitting diode), LP (Laser + Photosensitizer/Nanoparticle) and LEDP (LED + Photosensitizer/Nanoparticle). A multispecies biofilm composed ofS. gordonii, S. oralis, S. mitis, and S. sanguinis was grown in microplates containing BHI supplemented with 1% sucrose (w/v) for 24 h. Light irradiations were applied with a laser at 9 J for 90 s (320 J/cm²), or with LED, at 8.1 J for 90 s (8.1 J/cm²). The microbial reduction was assessed by counting viable biofilm microorganisms in selective culture media, before and after the treatments. Data normality was assessed by the Shapiro-Wilk test, and the results were submitted to Kruskal-Wallis analysis, followed by Dunn's test, with a significance level of 5%.

Results: The groups LP and LEDP were able to significantly reduce the biofilm microorganism counts by as much as 4 log₁₀ times compared to the negative control group (p < 0.05) and did not statistically differ from the positive control group (CX) (p > 0.05).

Conclusion: The A-PDT mediated by encapsulated β-cyclodextrin methylene blue irradiated by Laser or LED was effective in the microbial reduction of multispecies biofilm composed of early colonizing microorganisms.

Keywords: Biofilms; Nanoparticles; Photodynamic therapy; Streptococcus gordonii; Streptococcus mitis; Streptococcus oralis; Streptococcus sanguis.