The washed P. gingivalis suspensions were adjusted to an optical density of 0.6 at 550 nm and added to a 96-well plate at 150 µL per well, and then irradiated with 0, 1, 10, or 100J (1J; 400 mW/cm2, 2.5 sec. 10J; 400 mW/cm2, 25 sec. 100J; 400 mW/cm2, 250 sec). The survival of the P. gingivalis cells was estimated from viable bacteria by counting the number of CFUs 5 days after culture on BHI agar media under anaerobic conditions. The data is shown as the logarithm of CFU per milliliter.