Shigella dysenteriae is a species of the rod-shaped bacterial genus Shigella. They are normal inhabitants of the human gastro-intestinal tract and can cause shigellosis (bacillary dysentery). Shigellae are Gram-negative, non-spore-forming, facultatively anaerobic, non-motile bacteria.

S. dysenteriae, spread by contaminated water and food, causes the most severe dysentery because of its potent and deadly Shiga toxin, but other species may also be dysentery agents.

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