Step 1: Understanding the Concept:
Koch's postulates are a set of four criteria formulated by Robert Koch to establish a causal relationship between a specific microbe and a specific disease.
Step 2: Detailed Explanation:
Robert Koch developed his foundational postulates in the late 19th century through his research on anthrax, a disease affecting livestock and humans caused by the spore-forming bacterium Bacillus anthracis.
Koch isolated the bacterium from the blood of infected animals, grew it in pure culture, injected it into healthy laboratory animals, reproduced the disease, and re-isolated the same pathogen from the newly infected animals.
This experimental sequence established Bacillus anthracis as the specific cause of anthrax and formed the basis for his postulates.
Although Koch later used these postulates to identify the causative agents of tuberculosis (A) and cholera, his initial formulation and validation of the postulates were based on his studies of anthrax.
Hepatitis (B) is caused by viruses, which could not be cultured on artificial media, and Mycobacterium leprae (the cause of leprosy (C)) is an obligate intracellular pathogen that also cannot be grown in pure culture, making them unsuitable for his early postulates.
Step 3: Final Answer:
Therefore, the postulates were based on his studies of anthrax, corresponding to option (D).