Objective: To examine whether endogenous S. sanguis could prevent, or reduce the colonization of the virulent P. gingivalis strain.
Methods: First, 10 specific pathogen-free Wistar rats were divided into 2 groups. Doxycycline was administered in the drinking water for 7 days. Successful implantation of the endogenous strain of S. sanguis, isolated from one of the rats before doxycycline administration, and P. gingivalis 381 within 14 days of observation were demonstrated in the rats of each group respectively. Then, 30 SPF rats were divided into 6 groups. Doxycycline was administered in the drinking water for 7 days to all the rats. Afterwards, the rats in group A and B were inoculated orally once a day for 5 days with P. gingivalis, the rats in group C and E were inoculated orally once a day for 5 days with S. sanguis. Then, the rats in group A were inoculated for 5 days with S. sanguis, and rats in group C and D were inoculated for 5 days with P. gingivalis. The rats in group F served as negative control. After inoculation, the levels of S. sanguis and P. gingivalis in the mouths of the rats were determined after 12, 24, 36 hours, 7 days and 14 days.
Results: Both pre-colonization of S. sanguis and superinfection with S. sanguis did reduce the level of P. gingivalis in experimental rats. However, the reduction only maintained quite short time, about 36 hours. It was not caused by the decreased level of S. sanguis after 36 hours because the level of S. sanguis kept stable during the observation period of 14 days.
Conclusion: That S. sanguis function as the effector strain requires the successful implantation of S. sanguis as well as S. sanguis producing antagonistic action efficiently in vivo.