Question

Microbiology: 1. Explain how you would use Robert Koch's postulates to determine that Bacterium HU220 is the causative agent of the disease XYZ. Also, explain why Koch's postulates cannot be fulfilled for some microorganisms. 2. Discuss the role of phages in bacterial pathogenesis. 3. The complement system functions as a mediator of both innate and adaptive host defense mechanisms. Given your knowledge of host-defense system, discuss the role played by the complement system in both adaptive and innate immunity, 4. Explain the concept of semiconservative replication and how simultaneous copying of both strands of DNA is accomplished in prokaryotic cells. Include as much detail as you can regarding DNA replication. 5. Explain the differences between defined and complex media, and selective and differential media. Additionally, design an experiment using media to characterize bacteria isolated from soil. Include any laboratory techniques you would use.

Answer 1

Answer 1:

The four criteria put forth by Robert Koch must be met to determine that Bacterium HU220 is the causative agent of the disease XYZ. In order to determine if Koch's criteria are met, tests would be performed on laboratory animals and cultures from healthy as well as animals that have the disease XYZ and compared for the following:

1) Bacterium HU220 would be absent from all healthy organisms but present in all diseased organisms

2) Bacterium HU220 isolated from organisms with XYZ disease should be able to grow as pure culture

3) The pure culture of Bacterium HU220 should cause the disease XYZ when inoculted into healthy susceptible individuals.

4) The Bacterium HU220 should be re-isolated from the inoculated, diseased organism

Koch's postulates cannot be fulfilled for microorganisms:

1) that cannot be grown in pure culture such as obligate intracellular parasites (or virus)

2) that might not be present at every stage of the disease. For example V. cholerae may not be present at the time of severe diarrhoea or vomiting because the bacteria releases the toxins which causes the symptoms even in its absence.

3) that cause Polymicrobial infections

4) that has no animal model of infection