Fusobacteria

Fusobacteria are a diverse group of Gram-negative, anaerobic, non-spore-forming bacteria characterized by a slender, spindle-shaped morphology. The term commonly refers to species within the genus Fusobacterium, which belong to the phylum Fusobacteriota. These organisms are part of the normal microbiota of the human oral cavity, upper respiratory tract, gastrointestinal tract, and female genital tract, where they typically exist as obligate anaerobes in polymicrobial communities. They are generally non-motile and do not form endospores; cultivation requires strict anaerobic conditions.

Infections with fusobacteria occur mainly in the context of disrupted mucosal barriers or polymicrobial invasion. Fusobacterium necrophorum is a well-known pathogen associated with acute pharyngitis and the severe Lemierre’s syndrome, a septic thrombophlebitis of the internal jugular vein following a sore throat. Fusobacterium nucleatum and other fusobacteria are linked to periodontal disease, adverse pregnancy outcomes, intra-abdominal infections, and various soft-tissue and head-and-neck infections. These organisms are often involved in mixed anaerobic infections and can contribute to tissue invasion through adhesins and inflammatory mediators.

Diagnosis relies on anaerobic culture or molecular methods such as PCR and MALDI-TOF mass spectrometry, aided by clinical context. Treatment typically includes anaerobic coverage with metronidazole or a beta-lactam antibiotic, often combined with a beta-lactamase inhibitor, and source control in abscesses. Resistance patterns vary; susceptibility testing guides therapy when available. Overall, fusobacteria are clinically significant due to their role in both localized infections and rare but serious systemic disease.