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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
Figure 1.4
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Koch's Postulates
Postulate 1
The suspected
pathogenic organism
should be present in
all cases of the
disease and absent
from healthy animals
Postulate 2
The suspected
organism must be
isolated and grown in a
pure culture
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Postulate 3
Cells from a pure
culture of the
suspected organism
should cause disease
in a healthy animal
Postulate 4
The organism must be
re-isolated and shown
to be the same as the
origninal
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Using Koch’s Postulates
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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
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