Koch’s postulates

Koch's postulates are a set of four criteria developed by German physician Robert Koch to establish a causal relationship between a specific microorganism and a specific disease. These postulates are foundational to bacteriology and are essential for identifying the causative agents of infectious diseases.123

The four postulates are:
1. The microorganism must be present in all cases of the disease and absent in healthy individuals.
2. The microorganism must be isolated from the diseased host and grown in pure culture.
3. The cultured microorganism must cause the same disease when introduced into a healthy host.
4. The microorganism must be re-isolated from the newly infected host and be identical to the original causative agent.123

While crucial, these postulates have limitations, particularly for pathogens that are difficult to culture or cause asymptomatic infections. Koch's work also led to the discovery of the bacteria responsible for tuberculosis and cholera.13