Koch's postulates

Koch's postulates ( /ˈkoʊk/) are four criteria designed to establish a causal relationship between a causative microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884 and refined and published by Koch in 1890.

Koch's postulates are:

1.   The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.

2.   The microorganism must be isolated from a diseased organism and grown in pure culture.

3.   The cultured microorganism should cause disease when introduced into a healthy organism.

4.   The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.