Bacteroides /bak′təroi″dēz/ [Gk, bakterion, small staff, eidos, form] , a genus of obligate anaerobic bacilli normally found in the colon, mouth, genital tract, and upper respiratory system. Severe infection may result from the invasion of the bacillus through a break in the mucous membrane into the venous circulation, where thrombosis and bacteremia may occur. Foul-smelling abscesses, gas, and putrefaction are characteristic of infection with this organism. Of the 30 species, Bacteroides fragilis is the most common and most virulent.
