High Quality Content by WIKIPEDIA articles! Shigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During infection, it typically causes dysentery. The genus is named after Kiyoshi Shiga, who first discovered it in 1898.