Antimicrobial photodynamic therapy using a plaque disclosing solution on Streptococcus mutans

Abstract

Objectives: Photodynamic therapy with a bactericidal action is called antimicrobial photodynamic therapy (aPDT),which is a method of staining an object with a photosensitizing dye and then sterilizing by irradiating the dye at it's excitation wavelength. In this study, we aimed to investigate a caries pathogenic bactericidal method in a site difficult to mechanically remove, by examining aPDT effect on Streptococcus mutans (S. mutans), which is a typical caries pathogenic bacteria by applying the plaque disclosing solution as photosensitizing dye.

Methods: The absorption wavelength spectrum of irradiating plaque staining agent phloxine B (PB) was analyzed using UV-vis. Reactive oxygen species (ROS) generated by photo excitation with blue LED irradiation was measured by electron spin resonance technique. S. mutans was cultured according to a conventional method and the effect of aPDT after PB staining was evaluated by a Colony Forming Unit (CFU). In addition, protein carbonyl (PC), an oxidative stress marker, was also measured by western blotting.

Results: Singlet oxygen was generated by PB with blue light. As a result of aPDT treatment on S. mutans under this condition, it was recognized that CFU was suppressed dependent on irradiation intensity of blue light. In addition, the expression of PC was enhanced by aPDT.

Conclusions: aPDT is demonstrated by staining S. mutans with PB and irradiating blue light used for resin polymerization and tooth bleaching to generate ROS. Therefore, plaque-disclosing solution-based aPDT against S. mutans might represent a new method for cleaning pit and fissure grooves.

Keywords: Antimicrobial photodynamic therapy; Blue light; Oxidative stress; Plaque disclosing solution; Reactive oxygen species; Streptococcus mutans.