Balantidium coli is ingested in contaminated food and water in the cyst form. The cysts then migrate to the intestines, cecum, and terminal ileum where they break open to release the trophozoite. The trophozoites released in the intestines will multply by feeding on bacteria and replicate by binary fission, during which conjugation may occur. They usually reside in the lumen of the large intestine, but can penetrate the mucosa and secrete a substance to destroy intestinal tissue and create ulcers. The trophozoites will eventually form new mature cysts to be passed on through the digestive tract so that they can infect a new host. Thus, the parasite exists as two forms in its life cycle; the cysts and the trophozoites.