Use of visible light-based photodynamic therapy to bacterial photoinactivation

The main focus of this laboratory exercise was to investigate the photodynamic therapy (PDT) acting over Streptococcus mutans. A handheld photopolymerizer and a classical photosensitizer (Rose Bengal) were used to induce photodynamic response. In this way, a suspension of S. mutans was treated with different concentrations of Rose Bengal (0-10 μmol/liter), irradiated with a light (400-600 nm) for 20 s, and then cell viability was evaluated. It was observed that the light (per se) is not toxic, and in the dark, Rose Bengal is toxic only to the cells tested at concentrations above 5.0 μmol/liter. Under light exposure, concentrations of Rose Bengal above 0.5 μmol/liter killed all S. mutans. Therefore, for the purpose of our work, the photoactivation of Rose Bengal using the handheld photopolymerizer was efficient in bacteria inactivation.