The susceptibility of oral bacteria to antibacterial photodynamic therapy

It has been found that the oral cavity and tongue are the second abundant habitats of bacteria in the body. The oral microbiome is essential to maintain oral health, while it also has the potential to cause disease due to having pathogens simultaneously. In this study, seven oral bacterial strains which are known to be associated with an oral disease were selected to evaluate the antibiotic susceptibility to four different photosensitizers (PSs). Stock solution (1 mg/mℓ) of four PSs was prepared by dissolving the powder in dimethyl sulfoxide for curcumin and protoporphyrin IX, and distilled water for resazurin and riboflavin. The inoculation of 20 μℓ of a 24 h cultured bacterial suspension mixed with 1,980 μℓ each test solution and then a light source was placed in front of the mixed solution. The LED excitation wavelength was 405 nm and its energy was 84.5 mW/cm² for 300 s. Bacterial viability was determined by measuring the absorbance at 655 nm with a microplate reader. It was found that all PSs affect the viability of some oral bacteria by irradiated with light. The antibacterial susceptibility on the different PSs and visible blue light irradiation were different depending on each bacterial strain. Moreover, the same bacterial strain showed different effects depending on the type of the PSs. From the above results, antibacterial photodynamic therapy composed of light source and photosensitizers can be used to control the oral bacteria strains which are related to oral disease.