PERIODONTAL BONE LOSS IN PORPHYROMONAS-GINGIVALIS-INFECTED SPECIFIC PATHOGEN-FREE RATS AFTER PREINOCULATION WITH ENDOGENOUS STREPTOCOCCUS-SANGUIS

Anaerobic Gram-negative bacteria dominate in periodontitis locations, while Gram-positive bacteria characterize healthy sites. A well-established Gram-positive flora might therefore inhibit the colonization of Gram-negative pathogens. The purpose of the present investigation was to examine whether endogenous S. sanguis could prevent, or reduce, periodontal bone loss in rats infected with a virulent P. gingivalis strain. Sixty specific pathogen-free Wistar rats were divided into 6 groups. Doxycycline was administered in the drinking water for 2 weeks to the groups A, B, C, and D to suppress the preexisting microflora in the mouth. Rats in groups A and C were subsequently inoculated with an S. sanguis strain, isolated from one of the rats, once a day for 5 d. Infection with P gingivalis 381 was then carried out for 5 d in groups A, B, and E. Group F was not treated with doxycycline nor infected with bacteria and served as untreated control. Six weeks after the P gingivalis inoculation, the rats were killed. Periodontal bone levels were assessed radiographically and morphometrically, and serum antibody against P gingivalis 381 was determined by a fluorescence immunoassay. Periodontal bone support, determined radiographically, was reduced in group B (doxycycline-treated, P gingivalis-inoculated) compared with the other groups. In contrast, the morphometric determination showed no differences between the groups. In group B antibody levels against two different P gingivalis 381 cell surface antigens were significantly elevated. The data indicated that the preinoculation of an endogenous S. sanguis strain protected against a reduction of the radiographically assessed periodontal bone support induced by P gingivalis 381, and similarly prevented an elevation of the total serum antibody response to P gingivalis 381.