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Koch’s Rules

In order to provide the relationship of an organism to a disease Koch proposed rules which must be fulfilled. The finding of an organism in diseased tissues is not enough proof that the organism is the cause. Koch found that:

1. The organism must be found in each case of disease.

2. The organism must be isolated and grown in pure culture.

3. The organism must reproduce the disease in the susceptible animal or in suitable experimental animals.

4. The organism must be isolated from the tissues of the experimental animal in pure culture.

These rules have been of great value in the study of infectious diseases since the time of Koch, and the observance of them has formed a firm basis for medical bacteriology.