Porphyromonas gingivalis
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
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.

In patients harbouring porphyromonas gingivalis one finds high levels of specific antibody in the serum.

Additionally Porphyromonas gingivalis has been linked to Rheumatoid Arthritis. Porphyromonas gingivalis contains the PAD (Peptidyl-Arginine Deaminase) which is involved in citrullination. Patients with Rheumatoid Arthritis have an increased incidence of periodontal disease and antibodies to the bacterium are significantly more common in patients with Rheumatoid Arthritis