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Bacteria, Viruses, and Protists

Historical Interest in Bacteria

What are Koch’s postulates?

German bacteriologist Robert Koch (1843–1910) was the first to identify that various microorganisms are the cause of disease. His four basic criteria of bacteriology, known as Koch’s postulates, are still considered fundamental principles of bacteriology.

The postulates are the four basic criteria an organism must meet in order to be identified as pathogenic (capable of causing disease). The characteristics are as follows: 1) the organism must be found in tissues of animals that have been infected with the disease, rather than in disease-free animals; 2) the organism must be isolated from the diseased animal and grown in a pure culture or in vitro; 3) the cultured organism must be able to be transferred to a healthy animal, which will show signs of the disease after having been exposed to the organism; and 4) the organism must be able to be isolated from the infected animal.



French chemist and microbiologist Louis Pasteur was the first to realize that fermentation resulted from a biological process.

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