Question

Which of the following is not one of Koch's postulates?
a. The same pathogen must be present in every case of the disease.
b. The pathogen must be isolated and grown in pure culture from the diseased host.
c. The pathogen from pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
d. The disease must be transmitted from a diseased animal to a healthy, susceptible animal by direct contact.
e. The pathogen must be isolated in pure culture from an experimentally infected lab animal.

Accepted Answer

Step 1: Recall Koch's postulates, which are a set of criteria established to link a specific microorganism to a specific disease. These postulates include: the pathogen must be found in all cases of the disease, it must be isolated and grown in pure culture, it must cause the disease when introduced into a healthy host, and it must be re-isolated from the experimentally infected host. Step 2: Examine each option and compare it to the known Koch's postulates. Options a, b, c, and e align with the classical postulates: presence in every case, isolation in pure culture, causing disease in a healthy host, and re-isolation from the infected host. Step 3: Identify option d, which states that the disease must be transmitted by direct contact from a diseased animal to a healthy one. This is not part of Koch's original postulates, as they do not specify the mode of transmission but focus on isolation and causation. Step 4: Understand that Koch's postulates focus on establishing causality through isolation and infection, not on the mechanism of transmission such as direct contact. Step 5: Conclude that option d is not one of Koch's postulates because it introduces a transmission method rather than a criterion for establishing the causative agent of disease.

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Key Concepts

Koch's Postulates

Pure Culture Isolation

Disease Transmission and Experimental Infection