Koch's Postulates

Koch's postulates are a set of principles proposed by German physician and microbiologist Robert Koch in the late 19th century. These postulates establish criteria for determining the cause-and-effect relationship between a pathogen and an infectious disease.

Koch's postulates include:

1. The pathogenic microorganism must be present in all organisms with a given disease, but absent in healthy organisms.

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

3. When a pure culture of a microorganism is introduced into a susceptible organism, the same disease should develop.

4. The pathogen must be isolated again from the experimentally infected organism.

Although Koch's postulates played an important role in the development of microbiology, it is now known that some infectious agents do not meet all these criteria. Nevertheless, Koch's postulates remain fundamental principles for establishing cause-and-effect relationships in infectious pathology.