Table 1.

Koch's postulates to identify the causative agent of an infectious disease.

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

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

•The microorganism (from the pure culture) should cause disease when inoculated into a healthy organism

•The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent

^aKoch dismissed the universal requirement of the first postulate following the discovery of asymptomatic carriers of diseases such as cholera.