Which organism did Koch identify as the cause of anthrax?

• A. Bacillus cereus
• B. Bacillus anthracis
• C. Staphylococcus aureus
• D. Escherichia coli

Answer: (B)

Koch showed that a disease can be traced to a specific bacterium by isolating it from sick animals, growing it in pure culture, and proving it can produce the disease when introduced into a healthy host. The organism he identified as the cause of anthrax is Bacillus anthracis, a rod-shaped, Gram-positive, spore-forming bacterium. Its ability to form spores helped explain how anthrax persists in the environment and spreads. By re-isolating the same organism from the diseased experimental host, Koch established the causal link between Bacillus anthracis and anthrax. The other microbes listed are not the agents of anthrax: Bacillus cereus is associated with food poisoning, Staphylococcus aureus with various skin and wound infections, and Escherichia coli with intestinal disease; none are the cause of anthrax.