Answer:
B. The pathogen must be grown in pure culture.
Explanation:
Virus, and also some bacteria can not be cultured in "lifeless media". In the case of bacteria, we refer to the obligate intracellular ones, and all virus. Thus, this postulate can not be fulfilled in all cases. Virus can be propagated on tissue cultures, but certainly this was not considered by Koch. Moreover, these methods often result in spontaneous genetic alterations, which leads to adaptation and even attenuation in animal models of disease, so, the cultured virus perhaps does not induce the same disease when introduced to another specimen.
