A LOGICAL MECHANISM FOR DETERMINING THE CAUSE OF DISEASES WITH NEAR CERTAINTY Koch’s Postulates

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.