A medical principle known as Koch’s postulates outlines the criteria for establishing that a specific microorganism causes a particular disease. These criteria include: (1) The microorganism must be found in every case of the disease; (2) It must be isolated and grown in a pure culture; (3) When this culture is introduced into susceptible animals, it should lead to the development of the disease; and (4) The same microorganism must be re-isolated from these affected animals and grown in a pure culture again.