Prevotella melaninogenica endotoxin contains no heptose or 2-ketodeoxyoctanate, and it and the endotoxin of P oralis both show weak biologic activity. Poor biologic activity of endotoxin also has been demonstrated for the closely related species B thetaiotaomicron, B ovatus, B vulgatus, and B distasonis. This endotoxin exhibits little biologic activity in various test systems and little chemotactic activity what activity there is is complement-mediated by the alternative pathway. Numerous studies of the endotoxin of Gram-negative anaerobic bacilli have determined that the B fragilis endotoxin contains little or no lipid A, 2-ketodeoxyoctanate, or heptose. These genera contain numerous other species that rarely or never infect humans.Ĭolony morphology of P melaninogenica. Fusobacterium nucleatum is the Fusobacterium species most often found as a pathogen, but F necrophorum occasionally produces serious disease. Porphyromonas species seem to be much less pathogenic except in dental infections. Among the bile-sensitive Prevotella species, the ones most commonly encountered clinically are P melaninogenica, P oris, and P buccae. Within the Bacteroides group, B fragilis is the most common pathogen, followed by B thetaiotaomicron and other members of the B fragilis group. These genera are prevalent in the body as members of the normal flora ( Fig.20-1), constituting one-third of the total anaerobic isolates from clinical specimens, and may become involved in infections throughout the body ( Fig.20-2). ![]() ![]() In most clinical infections, only the genera Bacteroides, Prevotella, and Fusobacterium need be considered. At present there are over two dozen genera of Gram-negative anaerobic bacilli.
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