Bactericidal effect of hydroxyl radical generated by photolysis of hydrogen peroxide

Abstract

The relationship between the yield of hydroxyl radical generated by photolysis of H2O2 and its bactericidal effect was evaluated. To generate hydroxyl radical, H2O2 was irradiated with laser light at a wavelength of 405 nm. ESR spin trapping analysis showed that the yield of hydroxyl radical increased with either the laser irradiation time or the concentration of H2O2. Streptococcus mutans and Porphyromonas gingivalis were used in the bactericidal assay. The assay showed that the bactericidal effect was related to the laser irradiation time and the concentration of H2O2. Laser irradiation of the planktonic and the biofilm model of S. mutans in 1,000 mM H2O2 and P. gingivalis in 500 mM showed a >5-log reduction of viable counts within 3 min and 30 s, respectively. These results suggest that the bactericidal activity against oral pathogenic bacteria consisting of facultative and obligate anaerobes is dependent on the yield of hydroxyl radical.