dysentery caused by gram-negative rod-shaped enteric bacteria (enterobacteriaceae), most often by the genus SHIGELLA. Shigella dysentery, Shigellosis, is classified into subgroups according to syndrome severity and the infectious species. Group A: shigella dysenteriae (severest); Group B: shigella flexneri; Group C: shigella boydii; and Group D: shigella sonnei (mildest).