Bacteroidaceae: A family of gram-negative bacteria found primarily in the intestinal tracts and mucous membranes of warm-blooded animals. Its organisms are sometimes pathogenic.Fusobacterium: A genus of gram-negative, anaerobic, rod-shaped bacteria found in cavities of humans and other animals. No endospores are formed. Some species are pathogenic and occur in various purulent or gangrenous infections.Bacteroides: A genus of gram-negative, anaerobic, rod-shaped bacteria. Its organisms are normal inhabitants of the oral, respiratory, intestinal, and urogenital cavities of humans, animals, and insects. Some species may be pathogenic.Bacteroidaceae Infections: Infections with bacteria of the family BACTEROIDACEAE.