Any of the rod-shaped bacteria that make up the genus Shigella , which are normal inhabitants of the human intestinal tract and can cause dysentery , or shigellosis.
Shigellae are gram-negative (see gram stain ), non-spore-forming, stationary bacteria. S. dysenteriae , spread by contaminated water and food, causes the most severe dysentery because of its potent toxin, but other species may also be dysentery agents.