Infections Caused by Fusobacterium Species: Microbiology, Clinical Syndromes and Management: A Narrative Review

Fusobacterium spp. are Gram-negative, obligate anaerobic bacteria associated with a broad clinical spectrum, including head and neck infections; soft tissue infections; gastrointestinal and genitourinary infections; and bacteremia without an identified source. Clinical manifestations vary by species and site of colonization. F. necrophorum is linked to head and neck infections that may culminate in Lemierre syndrome, a life-threatening septic thrombophlebitis of the internal jugular vein. Although Fusobacterium bacteremia is uncommon, it is associated with substantial mortality. F. necrophorum bacteremia may occur as a complication of head and neck infection in younger, healthy individuals, whereas F. nucleatum bacteremia is reported predominantly in older patients with malignancy, secondary to an abdominal source or without an identified origin. Fusobacterium isolates are usually susceptible to penicillins, cephalosporins, aminopenicillins with β-lactamase inhibitors, carbapenems, and metronidazole, while resistance to clindamycin and moxifloxacin has been increasingly reported. Because susceptibility testing is not routinely performed and susceptibility data remain limited, severe infections are commonly treated with a β-lactam/β-lactamase inhibitor, a carbapenem, or a β-lactam in combination with metronidazole. This review provides an overview of the microbiology, clinical spectrum, and treatment of Fusobacterium spp.