fusobacterium polymorphum fusobacterium polymorphum fusobacterium polymorphum is a bacterium that has been isolated from the gingival crevice in humans, and has been implicated in the immunopathology of periodontal disease. it has also been isolated in guinea pigs in research studies. fusobacterium polymorphum scientific classification domain: bacteria phylum: fusobacteriota class: fusobacteriia order: fusobacteriales family: fusobacteriaceae genus: fusobacterium species: f. polymorphum binomial name fusobacterium polymorphumknorr, 1922