Summary auto-generated
Fusobacteria are obligately anaerobic gram-negative bacilli that have caused significant taxonomic confusion since their discovery in the late 19th century. This review addresses the nomenclature changes, modern classification using molecular techniques, laboratory identification methods, and clinical significance of these organisms. Fusobacteria are differentiated from related bacteria by their unique production of n-butyric acid as the sole volatile fatty acid product. Recent molecular techniques, particularly DNA homology studies and 16S rRNA sequencing, have established new species and subspecies, including subdividing Fusobacterium necrophorum and F. nucleatum into subspecies. Laboratory identification traditionally relied on gas-liquid chromatography of fatty acid products, though phosphomycin sensitivity testing provides a practical alternative. Fusobacteria are involved in diverse human infections including oral and dental infections, septicaemia, lung abscess, brain abscess, and intra-amniotic infections. They are commonly found in mixed polymicrobial infections and possess virulence factors including lipopolysaccharide endotoxin, haemolysins, and β-lactamase production.
Key findings
- Molecular techniques including DNA homology and 16S rRNA sequencing have clarified fusobacterial taxonomy, establishing new species and subdividing F. nucleatum into four subspecies and F. necrophorum into two subspecies
- Fusobacteria produce n-butyric acid alone as a major metabolic end product, distinguishing them from bacteroides and other gram-negative anaerobes, which can be detected by gas-liquid chromatography
- Fusobacteria cause a wide spectrum of human infections originating primarily from oral and respiratory tract flora, including life-threatening conditions such as post-anginal septicaemia (necrobacillosis) and metastatic abscess formation
- Laboratory identification is challenging due to asaccharolytic nature and limited biochemical reactions; phosphomycin sensitivity testing offers a practical presumptive identification method when gas-liquid chromatography is unavailable
- F. necrophorum is the most clinically significant species in serious infections, producing lipase, haemolysin, and leukocidin, and is particularly associated with necrotising tonsillitis and metastatic complications
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Abstract
Fusobacteria are anaerobic gram-negative bacilli. Since the first reports in the late nineteenth century, various names have been applied to these organisms, sometimes with the same name being applied to different species. More recently, not only have there been changes to the nomenclature, but also attempts to differentiate between species which are believed to be either pathogenic or commensal or both. Because of their asaccharolytic nature, and a general paucity of positive results in routine biochemical tests, laboratory identification of the fusobacteria has been difficult. However, the application of novel molecular biological techniques to taxonomy has established a number of new species, together with the subspeciation of Fusobacterium necrophorum and F. nucleatum, and provided new methods for identification. The involvement of fusobacteria in a wide spectrum of human infections causing tissue necrosis and septicaemia has long been recognised, and, more recently, their importance in intra-amniotic infections, premature labour and tropical ulcers has been reported.