Koch's postulates
Japanese: コッホの原則（コッホの四原則）
Four criteria for proving that a specific microorganism causes a specific disease. Proposed by Robert Koch in 1884, this methodology became a foundation of microbiology.
Koch's postulates are four criteria for proving that a specific bacterium causes a specific disease. Proposed in 1884 by German bacteriologist Robert Koch.
First, the organism must be found in all cases of the disease. Second, it must be isolated in pure culture. Third, inoculating a healthy host with the pure culture must reproduce the disease. Fourth, the same organism must be re-isolated from that host.
This logical framework became the methodological foundation of microbiology. Today, however, with many unculturable bacteria and cases where multiple organisms cooperate to cause disease, situations where the postulates cannot be directly applied are increasing.
In fermentation research too, a similar line of reasoning is sometimes used to identify which microbe is responsible for which flavor.