History of medical microbiology — Koch's postulates were first fully satisfied using which bacterial pathogen as the model organism?

Introduction / Context:
Koch's postulates established a foundational framework for linking a specific microorganism to a specific disease. Knowing the first organism used to fulfill these criteria is part of core microbiology knowledge and illustrates how systematic experimentation advanced infectious disease science.

Given Data / Assumptions:

• Koch's postulates include isolation of the organism, growth in pure culture, reproduction of disease in a susceptible host, and re-isolation of the same organism.
• The question asks which pathogen was used first to satisfy these postulates.
• Context is late 19th-century microbiology.

Concept / Approach:
Robert Koch studied Bacillus anthracis during anthrax outbreaks in livestock. He demonstrated the presence of bacilli in diseased animals, cultivated them in pure culture, reproduced disease by inoculation into healthy animals, and re-isolated the same bacillus. This series of experiments fulfilled the postulates, making B. anthracis the historically correct answer.

Step-by-Step Solution:

Verification / Alternative check:
Subsequent applications to Mycobacterium tuberculosis further cemented the framework, but the inaugural full demonstration was with B. anthracis.

Why Other Options Are Wrong:

• Clostridium tetani/Corynebacterium diphtheriae/Salmonella Typhi: important pathogens, but not the first historically used to satisfy all postulates.

Common Pitfalls:
Confusing notable Koch discoveries (e.g., tuberculosis) with the very first application of the full postulate set.

Final Answer:
Bacillus anthracis