MFD.09

Question 1

Koch-Henle Postulates states:

Answer 1

• The organism must be present in all cases of disease and not present in healthy individuals
• The organism must be isolated in pure culture
• The isolated organism must cause disease in a suitable animal
• The organism must be reisolated from infected animal

Question 2

Under what circumstances is it NOT possible to fulfil Koch’s postulates for the following:

1) The organism must be present in all cases of disease, and not present in healthy individuals
2) The organism must be isolated in pure

Answer 2

1) : asymptomatic carriers (cholera, Neisseria meningitidis)
2) : viruses could not be cultured in 1900s. Prions are still difficult/impossible to culture
Some infections are polymicrobial (no single aetiological agent) e.g. oral diseases do not have a single aetiological agent, suggesting microbrial community is the aetiological agent.

Question 3

Under what circumstances is it NOT possible to fulfil Koch’s postulates for the following:
1) The isolated organism must cause disease in a suitable animal

Answer 3

1) animal models may not be available/may not be representative of human disease e.g. stomach ulcer bacteria had to be swollen by scientist researching antibiotic to prove

Question 4

When Koch’s postulates cannot be applied precisely:

5

Answer 4

• If no infecting organism can be detected
• If the bacteria cannot be grown in culture
• If no suitable animal model is available
• If more than one species of bacterium is involved
• If it is the level rather than just the presence of the infecting bacterium that is important

Question 5

How was Koch’s proof applied to B.antheacis infections?

Answer 5

1) Homogenise spleen of infected animal ( collect from patient)
2) Place inside mouse (infect 1st test animal)
3) mouse becomes infected
4) Culture the bacteria from blood of infected mouse in an Ox’s eye ( to culture the single bacterium) then place in a different mouse
5) Second mouse gets ill (therefore proving that single bacterium caused disease

Question 6

How do organisms cause disease?

Answer 6

transmission and pathogenesis

Question 7

What are the 6 ways bacteria are transmitted?

Answer 7

Implantation • In utero • Ingestion • Inhalation • Injection •

Question 8

What technology is used in Koch’s postulates in the modern era?

Answer 8

1. DNA analysis ( PCR, sequencing, hybridization) used to detect infectious agents (a and

Question 9

Why is DNA analysis used in Koch’s postulates?

Answer 9

1) as it sensitive (detects agents in the absence of disease)
2) quantitative (can determine the load of infectious agents)
3) circumvents the isolation of an infectious agent- how thO? idk mate