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A genus of nonmotile, aerobic to facultatively anaerobic bacteria (family Enterobacteriaceae) containing Gram-negative nonencapsulated rods. These organisms cannot use citrate as a sole source of carbon; their growth is inhibited by potassium cyanide and their metabolism is fermentative; they ferment glucose and other carbohydrates with the production of acid but not gas; lactose is ordinarily not fermented, although it is sometimes slowly attacked; the normal habitat is the intestinal tract of humans and of higher apes; all of the species produce dysentery. The type species is S. dysenteriae. [Kiyoshi Shiga]

- S. boydii a species found only in feces of symptomatic individuals; occurs in a low proportion of cases of bacillary dysentery.

- S. dysenteriae a species causing severe necrotizing dysentery in humans induced by a virulent shiga toxin found only in feces of symptomatic individuals; the type species of the genus S.. SYN: Shiga bacillus, Shiga-Kruse bacillus.

- S. flexneri a species found in the feces of symptomatic individuals and of convalescents or carriers; a common cause of dysentery epidemics, especially in Asia and the Middle East. Now known sometimes to be sexually transmitted through anal intercourse. SYN: Flexner bacillus, paradysentery bacillus.

- S. sonnei a species causing dysentery, sometimes milder than that caused by other species. The most common S. species causing disease in the U.S.

shi·gel·la shi-'gel-ə n

1) cap a genus of nonmotile aerobic bacteria of the family Enterobacteriaceae that form acid but no gas on many carbohydrates and that cause dysenteries in animals and esp. humans

2) pl -gel·lae -.ē also -gellas any bacterium of the genus Shigella

3) shigellosis

a genus of nonmotile rodlike Gram-negative bacteria normally present in the intestinal tract of warm-blooded animals. They ferment carbohydrates without the formation of gas. Some Shigella species are pathogenic. S. dysenteriae is associated with bacillary dysentery.