surginfection

Koch's postulates (1) the suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals, (2) the suspected pathogen should be isolated from a diseased host and grown in a pure culture in vitro, (3) cells from a pure culture of the suspected organism should cause disease in a healthy animal, and ( 4) the organism should be reisolated from the newly diseased animal and shown to be the same as the original.