He accomplished this in 1876 with his work on anthrax. He isolated the bacterium *Bacillus anthracis* from infected animals and showed that it could cause the disease when injected into healthy animals. This was a landmark discovery because it established the germ theory of disease.
It's worth noting that Louis Pasteur, a contemporary of Koch, also made significant contributions to the understanding of infectious diseases. He was the first to demonstrate that microorganisms cause fermentation and that these organisms could be killed by heat. However, it was Koch who definitively linked a specific microorganism to a specific disease through his meticulous experimental approach.
