Overview: Bacteria of genus Fusobacterium are abundant in the mouth, particularly in subgingival plaque, where they make up approximately 10% of the community, as well as in supragingival plaque and in samples from the palatine tonsils, tongue dorsum, throat, and saliva. Three subspecies of F. nucleatum, subspecies animalis, polymorphum, and vincentii, are abundant in dental plaque and the palatine tonsils, while F. periodonticum is abundant in samples from the tongue dorsum and from the tonsils, throat, and saliva.

Ecological role/importance in health and disease: In the dental plaque model of Kolenbrander and colleagues, F. nucleatum is considered the taxon that forms a bridge between early colonizers and later-colonizing periodontal pathogens (Kolenbrander & London 1993, Kolenbrander et al. 2010), although imaging-based evidence for its role as a physical bridge is lacking (Mark Welch et al. 2020). F. periodonticum and several subspecies of F. nucleatum (F. nucleatum subspecies nucleatum, polymorphum, and vincentii) are considered part of the "orange complex" in subgingival plaque marking part of the ecological succession from health toward periodontitis (Socransky et al. 1998).