n pl :  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  .
 
 
 
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