Which one of the following is not one of Koch's Postulates?

The same microorganisms must be present in every case of the disease.

The microorganism must be isolated and grown in pure culture from the diseased host.

The microorganism from pure culture must cause the disease when inoculated into a healthy, susceptible laboratory host.

The disease must be transmitted from a diseased host to a healthy, susceptible host by some form of contact.

The microorganism must be isolated in pure culture from an experimentally infected lab host.