Question

Koch’s postulates are not applicable to
A) T.B
B) Leprosy
C) Cholera
D) Diphtheria

Answer 1

Koch's postulates: In 1890, Robert Koch, a German physician and bacteriologist, set forth his celebrated criterion for determining whether a given bacteria is the cause of a given disease. Koch's criteria also provided some much-needed scientific clarity to what was then a somewhat confused area.

Complete answer:
The postulates of Koch are as follows:

In any case of the disease, the bacteria must be present.
The bacteria must be isolated from the disease host and grown in pure culture.
When the pure culture of the bacteria is inoculated into a healthy susceptible host, the same disease has to be replicated.
The bacteria must be retrieved from the experimentally contaminated host.

However, Koch's postulates have drawbacks, so it might not always be the last word. They will not be retained if:

Specific bacteria (such as the one that causes leprosy) can not be "grown in pure culture" in the laboratory.
There is no animal model of infection with this particular bacteria.

An inoffensive bacteria can cause disease if:

It has acquired extra virulence factors that make it pathogenic.
Access to deep tissue by trauma , surgery, IV line, etc.
Infects the immunocompromised patient.
Not all bacteria infected individuals may develop a disease. In general, subclinical infection is more common than a clinically evident infection..

Hence the correct answer is ption (B) Leprosy.

Note: Despite these limitations, Koch's conclusions are still a valuable benchmark in determining if there is a cause-and - effect relationship between a bacteria (or any other form of microorganism) and a clinical disease.