Bactericidal Effect of Photolysis of H(2)O(2) in Combination with Sonolysis of Water via Hydroxyl Radical Generation

The bactericidal effect of hydroxyl radical (·OH) generated by combination of photolysis of hydrogen peroxide (H(2)O(2)) and sonolysis of water was examined under the condition in which the yield of ·OH increased additively when H(2)O(2) aqueous solution was concomitantly irradiated with laser and ultrasound. The suspension of Staphylococcus aureus mixed with the different concentrations of H(2)O(2) was irradiated simultaneously with a laser light (wavelength: 405 nm, irradiance: 46 and 91 mW/cm(2)) and ultrasound (power: 30 w, frequency: 1.65 MHz) at 20 ± 1°C of the water bulk temperature for 2 min. The combination of laser and ultrasound irradiation significantly reduced the viable bacterial count in comparison with the laser irradiation of H(2)O(2) alone. By contrast, the ultrasound irradiation alone exerted almost no bactericidal effect. These results suggested that the combination effect of photolysis of H(2)O(2) and sonolysis of water on bactericidal activity was synergistic. A multi-way analysis of variance also revealed that the interaction of H(2)O(2) concentration, laser power and ultrasound irradiation significantly affected the bactericidal activity. Since the result of oxidative DNA damage evaluation demonstrated that the combination of laser and ultrasound irradiation significantly induced oxidative damage of bacterial DNA in comparison with the laser irradiation of H(2)O(2) alone, it was suggested that the combination effect of photolysis of H(2)O(2) and sonolysis of water on bactericidal activity would be exerted via oxidative damage of cellular components such as DNA.