Porphyromonas gingivalis belongs to the phylum Bacteroidetes and is a non-motile, Gram-negative, rod-shaped, anaerobic pathogenic bacterium. It forms black colonies on blood agar.
It is found in the oral cavity, where it is implicated in certain forms of periodontal disease, as well as the upper gastrointestinal tract, respiratory tract, and in the colon. Collagen degradation that is observed in chronic periodontal disease results in part from the collagenase enzymes of this species. It has been shown in an in vitro study that P. gingivalis can invade human gingival fibroblasts and can survive in them in the presence of considerable concentrations of antibiotics. link to wiki