Question

Which of the following statements is NOT true for Koch's postulates? (or Koch's first postulate)

• A. The microorganism must be present in every case of the disease.
• B. The specific disease must be reproduced when a pure culture of the microorganism is inoculated into healthy susceptible host.
• C. The causative agent of the disease must be present in every diseased host.
• D. The microorganism must be isolated from diseased host and grown in Mixed culture.

Hint:

The key to Koch's second postulate is the development of pure culture techniques.
Robert Koch and his assistant Julius Richard Petri (who invented the Petri dish) developed solid media methods using agar to isolate single bacterial colonies.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Robert Koch established a set of four scientific criteria, known as Koch's Postulates, to determine a causal relationship between a specific microorganism and a transmissible disease.
These postulates revolutionized the fields of medical microbiology and plant pathology.

Step 3: Detailed Explanation:
Let us review the four classical postulates formulated by Robert Koch:
1. The specific microorganism must be consistently associated with the disease, meaning it must be present in every diseased host and absent from healthy individuals. (This matches Statement A and Statement C).
2. The pathogen must be isolated from the diseased host and grown in an artificial medium as a pure culture containing only that specific organism.
3. The disease must be reproduced when the isolated organism from the pure culture is inoculated into a healthy, susceptible host. (This matches Statement B).
4. The same pathogen must be re-isolated from the experimentally infected host and shown to match the original culture.
Let us evaluate Statement (D):
Statement (D) suggests that the isolated microorganism is grown in a "mixed culture."
This contradicts the fundamental methodology of microbiology and Koch's postulates.
To establish a causal relationship, a pathogen must be isolated and grown as a pure culture (a clonal population of a single microbial species).
Growing the microbe in a mixed culture makes it impossible to determine which organism in the mixture is responsible for causing the disease.
Therefore, Statement (D) is incorrect.

Step 4: Final Answer:
The statement that is NOT true for Koch's postulates is Option (D).