German bacteriologist who demonstrated that specific diseases are caused by specific microorganisms. He identified the bacilli that cause anthrax, tuberculosis, and cholera, and he showed that fleas and rats are responsible for transmission of the bubonic plague and that the tsetse fly is responsible for transmitting sleeping sickness. Koch won the Nobel Prize for physiology or medicine in 1905.
Biography Robert Koch is deservedly famous for his discovery of the bacteria that cause tuberculosis and many other diseases, and his illumination of the life cycle of the anthrax bacillus in 1876 showed how a particular microorganism caused a particular disease, definitively establishing the modern germ theory of disease. What Koch is less well-known for is his equally important and pioneering work in laboratory methods, especially in culture techniques and microscopy. Some attempts before Koch had already been made to grow microorganisms outside the body, but it was he who, through ingenious experiments, devised cheap, reliable, and duplicable techniques for growing pure cultures of single species of bacteria in the lab. Except for the lid, he invented the petri dish and a jellylike culture medium for it (the lid was later added by one of his assistants, Julius Petri). For years a passionate amateur photographer, Koch soon applied that interest to his lab work: he devised methods for preparing and culturing bacteria in thin layers on glass slides so that they could be photographed under a microscope. He invented ways of staining bacterial cultures to make poorly visible bacteria stand out under magnification. All of these innovations allowed the life cycles of bacteria to be studied and documented for the first time—an advance that bore its first and perhaps most dramatic fruit in Koch's demonstration of the life cycle of the anthrax bacillus, which was accompanied by dramatic photographs that took the scientific world by storm.