ABSTRACT
The defi nitive proof that a specifi c bacterium caused a particular disease was fi nally provided by the German microbiologist Robert Koch in 1876 (Figure 5.22). Crucial to this endeavor was the development of pure culture technique. Koch realized that if a specifi c microorganism was causing disease, any host would also harbor many other microorganisms that may have nothing to do with the disease in question. Unless he could isolate these various microorganisms, he would have no means to determine exactly which species was actually the pathogen. Koch found that he could take samples from a host and spread them out on solid nutrients such as potato slices. Different microbial species grew into different shaped and colored colonies. He then inferred that each of these colonies had arisen from a single bacterial cell and consequently represented a pure culture. Cells could then be extracted from each of these colonies for further testing.
