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Figure 1.4

The Germ Theory of Disease

1876: Robert Koch proved that a bacterium causes anthrax and provided the experimental steps, Koch’s postulates, to prove that a specific microbe causes a specific disease

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Postulate 1Postulate 1The suspected The suspected pathogenic organism pathogenic organism should be present in should be present in all cases of the all cases of the disease and absent disease and absent from healthy animalsfrom healthy animals

Postulate 2Postulate 2The suspected The suspected organism must be organism must be isolated and grown in a isolated and grown in a pure culturepure culture

Koch's Postulates

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Postulate 3Postulate 3Cells from a pure Cells from a pure culture of the culture of the suspected organism suspected organism should cause disease should cause disease in a healthy animalin a healthy animal

Postulate 4Postulate 4The organism must be The organism must be re-isolated and shown re-isolated and shown to be the same as the to be the same as the origninalorigninal

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Using Koch’s Postulates 1882 – bacteria caused tuberculosis 1884 – bacteria caused cholera 1884 – bacteria caused Diphtheria 1884 – bacteria caused Typhoid Fever 1885 – bacteria caused Gonorrhea 1886 – bacteria caused pneumonia Etc. 2003 – Virus called SARS