1. A genus that includes many species of obligate anaerobic, non-spore-forming bacteria (family Bacteroidaceae) containing gram-negative rods. Both motile and nonmotile species occur; motile cells are peritrichous. Some species ferment carbohydrates and produce combinations of succinic, lactic, acetic, formic, or propionic acids, sometimes with short-chained alcohols; butyric acid is not a major product. Those species that do not ferment carbohydrates produce from peptone either trace to moderate amounts of succinic, formic, acetic, and lactic acids or major amounts of acetic and butyric acids with moderate amounts of alcohols and isovaleric, propionic, and isobutyric acids. They are part of the normal flora of the intestinal tract and to a lesser degree, the respiratory and urogenital cavities of humans and animals; many species formerly classified as Bacteroides have been reclassified as belonging to the genus Prevotella. Many species can be pathogenic. The type species is Bacteroides fragilis.
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