Koch's Postulates

Question 1

What are the 4 criteria for Koch’s postulates?

Answer 1

1) Microorganism must be found in abundance in organisms from disease but not in healthy individuals
2) Microorganism must be isolated from a diseased organism and grown in culture
3) Cultured microorganism should cause disease when introduced into a healthy organism
4) Microorganism must be re-isolated from inoculated, diseased host and identified as identical as original

Question 2

What are necessary and sufficient causes?

Answer 2

1) Necessary - must be present for disease to occur
2) Sufficient - guarantees disease will occur

Question 3

What is the major limit of Koch’s postulates today?

Answer 3

Many pathogens cannot be cultured/lack suitable animal models

Question 4

What are Molecular Koch’s postulates (Falkow, 1988)?

Answer 4

1) Gene must be linked to virulence
2) It’s deletion must reduce virulence
3) Reintroduction must restore it

Question 5

Why are original Koch’s postulates insufficient for modern microbiology?

Answer 5

Do not account for asymptomatic carriers, polymicrobial infections, unculturable microbes, or genetic mechanisms of disease

Question 6

What’s an example of a pathogen without an animal model?

Answer 6

Helicobacter pylori (proven by Barry Marshall) - drank it to prove it causes ulcers

Question 7

What is a polymicrobial infection?

Answer 7

An infection caused by multiple microbial species acting together

Question 8

What happens if a gene deletion affects general viability, not just virulence?

Answer 8

It cannot be used to claim the gene causes pathogenicity