Abstract
Introduction Titanium dioxide in the rutile-pellet form was used as a catalyst in the ultrasonic irradiation system to generate hydroxyl radicals in order to disinfect the water. Cultivated culture of Legionella was used for the kinetically investigation of cell destruction and its mechanism. The formation of active species such as hydroxyl radical, hydrogen peroxide, superoxide and etc can be promoted during ultrasonic irradiation in the presence of TiO_2. It may be due to the concentrated energy of the exploded bubbles on the surfaces of titanium granules caused during acoustic cavitations. These reactive oxygen species (ROS) may disrupt or damage various cell or viral functions and structures. Improvement of this novel disinfection method and studying the mechanism of this system were the purposes of this investigation. Materials and methods -Preparation of Cultures Legionella pneumophila(GIFU 9888) was used in this research as the model microorganisms. Legionella were incubated on BCYE plate and transferred to BYE medium. The inoculated culture was incubated in a shaker incubator at 110 rpm for 48 hrs at 37℃. Then, the culture broth was diluted to a suitable concentration. Ten ml of the diluted broth was transferred to the bottles containing TiO_2 pellets at different concentrations. -Ultrasonic irradiation Bottles were irradiated at 36 KHz, 300 W and samples were driven at different time courses. The temperature was kept constant at 20℃ during irradiation. The irradiated samples were diluted to suitable concentrations and plated on BCYE plates. The plates were incubated for 72 hrs at 37℃. The number of colonies on the plates was counted after incubation. Results and Discussion Ultrasonic irradiation of diluted culture for 15 minutes showed 92% reduction in the number of viable cell concentration at the presence of TiO_2. The rate of disinfection was compared in the presence of TiO_2 and Al_2O_3. TiO_2 induced higher rate of cell killing compared with Al_2O_3. Also, investigating the effect of TiO_2 concentration indicated that the rate of disinfection was proportional to the concentration of TiO_2. The mechanism of cell killing was further investigated by examining the effects of OH radical scavengers such as ascorbic acid and glutathione. Lower rates of disinfection were observed in the samples containing these radical scavengers, thus indicating the primary role of OH radicals in this process.
