Download Koch`s Postulates

Koch’s Postulates
A LOGICAL MECHANISM FOR
DETERMINING THE CAUSE OF DISEASES
WITH NEAR CERTAINTY
What do they do?
 Koch’s postulates provide a logical mechanism used
to prove that a specific microorganism causes a
specific disease with near certainty.
Overview of Koch’s Postulates
 Overall, Koch’s postulates state:
1)
The suspected pathogenic organism should be present in all
cases of the disease. In addition, the organism should be
absent from all healthy animals.
2) The suspected organism should be grown in pure culture, a
laboratory grown culture containing only one type of
microorganism.
3) If a healthy animal is inoculated with cells from the pure
culture, that is the cells are introduced to the animal’s body,
the animal should become diseased.
4) The pathogenic organism should be isolated from the newly
infected animal, grown in laboratory culture and be shown to
be identical to the original organism.
Source: Madigan, Martinko, Dunlap and Clark, p. 15 (2009).
Step One: Determine a suspected pathogen.
 Observe infected samples (blood, tissue, etc.).
 Should contain the suspected pathogen.
 Different staining techniques may be used to allow better
differentiation between cells.
 Observe healthy samples.
 Should not contain the microorganism.

If the suspected microorganism is present in the healthy animal it
can be concluded that it is not the pathogen for the target disease.
Step Two: Grow suspected organism in
laboratory culture.
 Grow a pure culture on a media.
 A culture media is a solution of various nutrients, such as
carbon, nitrogen, vitamins, sugars and amino acids, suitable
for the growth of microorganisms.
 Different types of media:
Solid, semi-solid and liquid
 Defined and complex

 Note: Choosing the proper media is essential because
different microorganisms will grow in certain conditions,
but not others.
Step Three: Test the isolated suspect organism.
 Inoculate a healthy test animal with the suspected
pathogen.


If the animal develops the disease, the microorganism may still
be the causative agent.
If the animal does not develop the disease, the organism is not
the causative agent.
Step Four: Reisolate the suspected pathogen.
 If the suspected pathogen caused disease in the test
animal:



Reisolate the microorganism from the animal.
Grow the microorganism in a pure culture.
Examine the microorganism.

If the microorganism is the same as the original organism used in
step two, it can be concluded that it is the causative agent of the
disease in question.
Source: Madigan, Martinko, Dunlap and Clark, p. 15 (2009).
Conclusion
 Koch’s postulates can determine with an
unparalleled amount of certainty that a
microorganism causes a specific disease.


Helps researchers understand the behavior of diseases.
Aids in the discovery of cures and vaccines.
 It is sometimes impossible to satisfy all of Koch’s
postulates.

Other methods must be employed to link a pathogen to a
specific disease.
 The logical mechanism can also be used in other
applications.
Bibliography
 Leboffe, M. J., & Pierce, B. E. (2006). Microbiology
Laboratory Theory and Application. Morton
Publishing Company.
 Madigan, M. T., Martinko, J. M., Dunlap, P. V., &
Clark, D. P. (2009). Brock: Biology of
Microorgansism. San Francisco: Pearson
Education, Inc.