What did Robert Koch contribute to the field of microbiology?

Robert Koch's contribution to microbiology is primarily recognized through the establishment of Koch's postulates, which are a series of criteria designed to identify the causative agents of infectious diseases. These postulates laid the groundwork for modern bacteriology by providing a systematic method for determining the relationship between a specific microbe and a specific disease. Koch's method required researchers to isolate the microbe from a diseased organism, grow it in pure culture, and then demonstrate that it could cause the disease when introduced to a healthy host.

This was a pivotal development because it helped to shift the understanding of disease causation from miasma and humoral theories to a more scientific basis involving microorganisms. Koch’s work ultimately led to the identification of many pathogens, which is essential for the field of microbiology and the development of treatments and vaccines.

In contrast, the other options reflect contributions made by other figures or different aspects of medical science. The discovery of penicillin is attributed to Alexander Fleming, vaccines were developed by several scientists including Louis Pasteur, and although significant in the history of microscopy, the creation of the first microscope is not attributed to Koch.