In the late nineteenth century, the German microbiologist Robert Koch established a set of procedures to identify, and confirm the causative agent of a particular infectious disease. The following four steps, which are still very much used today, are known as Koch’s Postulates.
1. A specific organism must be always be observed in association with the disease.
2, The same organism must be isolated from an infected host and grown in pure culture
3. When the organism from the pure culture is inoculated into a susceptible host organism, it must cause the same disease.
4. The infectious organism must be re-isolated from the diseased organism and then grown again in pure culture.
I came across this bag of infected oranges this morning, (Penicillium digitatum I think), and its very clear to see how the infection has spread. With some General Kitchen Agar, this could be used as a lovely little DIY/Kitchen demonstration of a very important microbiological concept.