Which of the following correctly lists the steps of Koch's postulates in order?

• A. 1. The microorganism must cause disease when introduced into a healthy host. 2. The microorganism must be reisolated from the experimentally infected host. 3. The microorganism must be found in all cases of the disease. 4. The microorganism must be isolated and grown in pure culture.
• B. 1. The microorganism must be isolated and grown in pure culture. 2. The microorganism must be found in all cases of the disease. 3. The microorganism must be reisolated from the experimentally infected host. 4. The cultured microorganism must cause disease when introduced into a healthy host.
• C. 1. The microorganism must be found in all cases of the disease. 2. The microorganism must be isolated and grown in pure culture. 3. The cultured microorganism must cause disease when introduced into a healthy host. 4. The microorganism must be reisolated from the experimentally infected host.
• D. 1. The microorganism must be reisolated from the experimentally infected host. 2. The microorganism must be found in all cases of the disease. 3. The microorganism must cause disease when introduced into a healthy host. 4. The microorganism must be isolated and grown in pure culture.

Answer: (C)

Verified step by step guidance

1. Understand that Koch's postulates are a series of criteria designed to establish a causative relationship between a microorganism and a disease.
2. Identify the first step: the microorganism must be found in all cases of the disease but not in healthy individuals. This establishes an association between the microorganism and the disease.
3. Next, the microorganism must be isolated from the diseased host and grown in pure culture. This step ensures that the microorganism can be studied independently.
4. Then, the cultured microorganism must cause the same disease when introduced into a healthy, susceptible host. This demonstrates causation.
5. Finally, the microorganism must be reisolated from the experimentally infected host and shown to be the same as the original microorganism. This confirms the link between the microorganism and the disease.