Genus Shigella is a group of bacteria responsible for causing diarrhea and other gastrointestinal illnesses in humans. The bacteria are commonly found in unsanitary environments and are transmitted through fecal-oral routes. There are several synonyms often used to refer to the genus Shigella. Some of these synonyms include Dysentery bacillus, Flexner bacillus, Shiga-Kruse bacillus, and Bacillus shigae. The term Shigella is derived from the name of a scientist named Kiyoshi Shiga who was instrumental in identifying the bacteria. The genus Shigella is composed of four species, S. sonnei, S. flexneri, S. boydii, and S. dysenteriae, each of which is further classified into multiple subtypes.