Robert Koch isolated Vibrio cholera and Mycobacterium
tuberculosis using not only sound microbiological techniques
but also rigorous epidemiological formulations. Koch noted
that a specific microorganism can be identified with disease if
it is present in all cases of disease and absent in health, if it
can be isolated from diseased animal and grown in pure
culture, and if the fresh microorganism, when inoculated into a healthy laboratory animal, caused the same disease seen in
the original animal and could be reisolated in pure culture
from the experimental infection.