Synergistic effect of proanthocyanidin on the bactericidal action of the photolysis of H²O²

The in vitro antibacterial activity of the hydroxyl radical generation system by the photolysis of H²O² in combination with proanthocyanidin, which refers to a group of polyphenolic compounds, was examined. Bactericidal activity of photo-irradiated H²O² at 405 nm against Streptococcus mutans, a major pathogen of dental caries, was augmented in the presence of proanthocyanidin, whose bactericidal effect by itself was very poor, in a concentration-dependent manner. This combination was also proven effective against Porphyromonas gingivalis, a major pathogen of periodontitis. It is speculated that H²O², generated from photo-irradiated proanthocyanidin around the bacterial cells, is photolyzed to the hydroxyl radical, which would in turn affect the membrane structure and function of the bacterial cells, resulting in augmented sensitivity of bacterial cells to the disinfection system utilizing the photolysis of H ²O². The present study suggests that the combination of H²O² and proanthocyanidin works synergistically to kill bacteria when photo-irradiated.