Principles of Disease and Epidemiology

7. Describe the significance of Koch’s postulates.

8. List Koch’s postulates.

9. Describe the applicability of Koch’s postulates.

10. List and describe the exceptions to Koch’s postulates.

The Etiology of Infectious Diseases

Koch’s Postulates

Koch’s postulates are criteria for establishing that specific microbes cause specific diseases.

Koch’s postulates have the following requirements:

The same pathogen must be present in every case of the disease.

The pathogen must be isolated in pure culture.

The pathogen isolated from pure culture must cause the same disease in a healthy, susceptible laboratory animal.

The pathogen must be reisolated from the inoculated laboratory animal.

Exceptions to Kochs Postulates

Kochs postulates are modified to establish etiologies of diseases caused by viruses and some bacteria which cannot be grown on artificial media.

Some diseases, such as tetanus, have unequivocal signs and symptoms.

Some diseases, such as pneumonia and nephritis, may be caused by a variety of microbes.

Some pathogens, such as S. pyogenes, cause several different diseases.

Certain pathogens, such as HIV, cause disease in humans only.