Bacillus anthracis, a Gram-positive, rod-shaped bacterium, causes anthrax. This is a deadly disease that can infect livestock and humans. It is the only permanent (obligated) pathogen in the genus Bacillus. Because it can be transmitted from animals to people, its infection is called zoonosis. Robert Koch, a German physician, discovered it in 1876. It became the first pathogen to be experimentally demonstrated. It was also the first scientific proof for germ theory.