Koch's postulates

The Koch's postulates (or Henle-Koch postulates) were formulated by Robert Koch, as a list of very strict requirements in order to validate the existence of a microorganism and a disease. Those postulates were formulated in 1884 to establish the etiology of tuberculosis, and were later redefined and published by Koch in 1890.

Used to confirm the etiological role of a microorganism in other diseases, these postulates were modified throughout the XX century according to the state of knowledge, the problems encountered and the appearance of new techniques. Since the 1980s, the postulates have had an adaptation based on molecular techniques.

Development

The postulates were formulated from Robert Koch's experiments with Bacillus anthracis. He showed that by injecting a small amount of blood from a diseased mouse into a healthy one, the latter would develop anthrax. By taking blood from the second animal and injecting it into another, he would again get the symptoms of the disease. After repeating the operation twenty times, he succeeded in culturing the bacterium in nutrient broths outside the animal and showed that, even after many culture transfers, the bacterium could cause disease when reinoculated into a healthy animal. They were applied to establish the etiology of anthrax, but it has been generalized to the rest of the infectious diseases in order to know which is the participating agent. The postulates are the following:

1. The pathogen must be present in sick animals and absent in healthy animals.
2. The agent must be cultivated in a pure axénic culture isolated from the animal's body.
3. The agent isolated in an axénic crop must cause disease in an animal susceptible to being inoculated.
4. The agent must be isolated again from the injuries produced in the experimental animals and be exactly the same to the original isolated.