Koch’s postulates [Robert Koch; L, postulare, to demand] , the prerequisites for experimentally establishing that a specific microorganism causes a particular disease. The following conditions must be met: (1) the microorganism must be observed in all cases of the disease; (2) the microorganism must be isolated and grown in pure culture; (3) microorganisms from the pure culture, when inoculated into a susceptible animal, must reproduce the disease; and (4) the microorganism must be observed in and recovered from the experimentally diseased animal.
