Chapter 1 - Koch's Postulates

Question 1

Koch’s First Postulate

Answer 1

The microorganism must be present in every case of the disease but absent from healthy organisms.

Question 2

Koch’s Second Postulate

Answer 2

The suspected microorganisms must be isolated from the infected organism and grown in a pure culture.

Question 3

Koch’s Third Postulate

Answer 3

The same disease must result when the isolated microorganism is inoculated I go a healthy host.

Question 4

Koch’s Fourth Postulate

Answer 4

The same microorganisms must be isolated again from the diseased host.

Question 5

List Koch’s Molecular Postulates

Answer 5

• The gene in question should be found in all pathogenic strains of the genus or species but be absent from nonpathogenic strains.
• Virulence of the microorganism with the inactivated gene must be less than that of the unaltered microorganism, in an appropriate animal model.
• The reintroduction of the gene into the microbe should restore the virulence in the animal model.
• The gene which causes virulence must the present again during expression.

Question 6

Why were Koch’s postulates slightly problematic?

Answer 6

1) Not all microorganisms can be grown in a laboratory in a pure culture e.g. viruses in host cells.
2) Some diseases are deadly and would be unethical to use on humans or animals in order to prove the postulates.

Question 7

What was the significance of Koch’s research in the world of Microbiology?

Answer 7

• It was used in the development of microbe isolating techniques.
• lead to the use of Petri dishes (discovered by Richard Petri in one of Koch’s labs)
• Agar was discovered by one of Koch’s associates wives, Fannie Hess. It has a melting point of 100 degrees instead of gelatin, where it is 28.
• Nutrient broth and agar mixture