Koch's postulates
noun pluralMedical Definition of Koch's postulates
: a statement of the steps required to establish a microorganism as the cause of a disease: (1) it must be found in all cases of the disease; (2) it must be isolated from the host and grown in pure culture; (3) it must reproduce the original disease when introduced into a susceptible host; (4) it must be found present in the experimental host so infected
— called also Koch's laws