Fusobacteria Fusobacteria are non-sporing, anaerobic, non-motile, non or weakly fermentative, spindle-shaped bacilli (with fused ends: hence the name). They are normal inhabitants of the oral cavity, colon and female genital tract and are sometimes isolated from pulmonary and pelvic abscesses. Fusospirochaetal infections, which they cause in combination with spirochaetes, are noteworthy. Fusobacterium nucleatum (the type species), and Fusobacterium periodontium are isolated mainly from periodontal disease sites. Fusobacterium alocis and Fusobacterium sulci are sometimes found in the healthy gingival sulcus.Non-oral species include Fusobacterium gonidiaformans, Fusobacterium russii and Fusobacterium ulcerans. Fusobacterium nucleatum Habitat and transmission Several subspecies of F. nucleatum have been identified in different habitats. These include F. nucleatum subsp. polymorphum, found in the healthy gingival crevice, and F. nucleatum subsp. nucleatum, recovered mainly from periodontal pockets. A third subspecies is F. nucleatum subsp. vincentii. Infections are almost invariably endogenous. Characteristics Gram-negative, strictly anaerobic, cigar-shaped bacilli with pointed ends. Cells often have a central swelling. A Gram-stained smear of deep gingival debris obtained from a lesion of acute ulcerative gingivitis is a simple method of demonstrating the characteristic fusobacteria, together with spirochaetes and polymorphonuclear leukocytes. These, together with the clinical picture, confirm a clinical diagnosis of acute ulcerative gingivitis. Culture and identification Grows on blood agar as dull, granular colonies with an irregular rhizoid edge. Biochemical reactions and the acidic end products of carbohydrate metabolism help in identification. As fusobacteria can remove sulphur from cysteine and methionine to produce odoriferous hydrogen sulphide and methylmercaptan, they are thought to be associated with halitosis. Pathogenicity The endotoxin of the organism appears to be involved in the pathogenesis of periodontal disease. It possesses remarkable adherence properties and the fusobacterium adhesin A (FadA), which confers this property has recently been isolated. F. nucleatum is usually isolated from polymicrobial infections; it is rarely the sole pathogen. Thus, in combination with oral spirochaetes (Treponema vincentii),I t causes the classic fusospirochaetal infections. These are: • acute (necrotizing) ulcerative gingivitis or trench Mouth. • Vincent’s angina, an ulcerative tonsillitis causing tissue necrosis, often due to extension of acute ulcerative gingivitis • cancrum oris or noma: a sequela of acute ulcerative gingivitis with resultant gross tissue loss of the facial region. As fusobacteria coaggregate with most other oral bacteria, they are believed to be important bridging organisms between early and late colonizers during plaque formation Antibiotic sensitivity and prevention Fusobacteria are uniformly sensitive to penicillin and, being strict anaerobes, are sensitive to metronidazole. Regular oral hygiene and antiseptic mouthwashes are the key to prevention of oral fusobacterial infections in individuals. Leptotrichia Leptotrichia spp. are oral commensals previously thought to belong to the genus Fusobacterium. They are Gram-negative, strictly anaerobic, slender, filamentous bacilli, usually with one pointed end. Leptotrichia buccalis, present in low proportions in dental plaque. The cell wall is similar to Gram-negative bacteria but stains poorly with the Gram stain. Underneath the cell wall run three to five axial filaments that are fixed to the extremities of the organism. Contractions of these filaments distort the bacterial cell body to give it its helical shape. The organism moves either by rotation along the long axis or by flexion of cells. Because of their weak refractile nature, dark-ground microscopy is used to visualize these organisms in the laboratory, although immunofluorescence is more useful for identification purposes. KEY FACTS • Fusobacteria are non-sporing, anaerobic, spindle-shaped bacilli inhabiting the oral cavity, colon and female genital tract. • The type species Fusobacterium nucleatum and Fusobacterium periodonticum are isolated mainly from periodontal disease sites and hence considered to be periodontopathic bacteria. • Fusospirochaetal infections caused by fusobacteria in combination with spirochaetes are acute ulcerative gingivitis, Vincent’s angina and cancrum oris (or noma). .