Periodontopathic potential of two strains of Porphyromonas gingivalis in gnotobiotic rats.

Germ-free rats were monoinfected with Porphyromonas gingivalis strains 381 or A7A1-28 for 42 or 84 days. Both strains induced substantial destruction of alveolar bone and soft tissue when compared to non-infected controls, but the patterns were different. Strain A7A1-28 was associated with increased activity of host collagenase and gelatinase at 42 days, whereas the activity was elevated to a lesser extent at 84 days. Strain 381 showed a moderate increase in host proteinase activity at 42 days, and this remained unchanged until day 84. Strain A7A1-28 was associated with more bone loss than strain 381 by a morphometric analysis that detects horizontal bone loss in the maxilla. Strain 381 was associated with more bone loss than strain A7A1-28 by a radiographic method that detects vertical intrabony defects in the mandible. Infection with one strain gave rise to serum and salivary antibodies strongly reactive to the infecting strain and moderately reactive to antigens from the other strain. This indicates that some antigenic similarity exists between the strains and that there are also strain or perhaps serotype differences in antibody responses induced by infection. Thus two strains of P. gingivalis differing in antigenicity and pathogenicity in the mouse model of the subcutaneous abscess cause substantial periodontal destruction in the germ-free rat. The disease pattern is, however, different, with strain A7A1-28 inducing mostly horizontal bone loss and strain 381 mostly vertical.