Infectious Diseases: Digestive System. Clostridium botulinum bacteria. Stomach and Intestines. Gastroenteritis is the inflammation of the gastrointes-. tinal tract (GI) which is composed of stomach and in-. testines. GI disease may be caused by many different. types of bacteria, viruses, and parasites. Symptoms of bacterial gastroenteritis may include ex -. cessive salivation, vomiting, diarrhea, straining, and. abdominal pain. If hemorrhages occur in the lining of. the lower portion of the GI tract, blood will be present.