Microbial Infection

Question 1

What is a capsid and what is its function?

Answer 1

Protective protein coat

Provides protection for the viral genome against environment; receptor recognition

Question 2

What is a spike projection (protein)?

Answer 2

Glycoprotein (found within phospholipid envelope) involved in receptor recognition and viral tropism (helping virus to productively infect a cell), e.g neuraminidase and haemagglutinin expressed on Influenza A

Question 3

Outline the steps of Mycobacterium tuberculosis infection.

Answer 3

1. Bacteria first encounters alveolar macrophages. Other macrophages and APCs recognise and phagocytose the bacteria (form a phagosome).
2. Phagosome matures and fuses with endosomes and lysosomes. Activation of macrophage by IFN-gamma promotes bacterial killing by ROI and RNI formation.
3. APCs and activated macrophages present antigen on MHC II molecules.
4. Specific CD4+ cells are activated, proliferate and differentiate into Th1 cells.
5. Th1 effector cells migrate to lungs through chemotaxis - release cytokines -increased macrophage activation and triggering of potent anti microbial activities.
6. Granuloma forms with centrally located macrophages (plus lymphocytes, NK cells, DCs, neutrophils)

Question 4

What happens in the pre-erythrocytic stage of the malaria cell cycle?

Answer 4

During mosquito bite, sporozoites are released from mosquito salivary glands:

• enter bloodstream
• circulate to the liver
• invade hepatocytes
• differentiate

After one week, infected hepatocytes rupture, releasing merozoites into the bloodstream that invade red blood cells.

Question 5

What happens in the erythrocytic/ blood-stage of the malaria cell cycle?

Answer 5

Parasite development: mature from rings to trophozoites to fully mature schizonts (contain 16-20 merozoites) over a 44-72 hr period. Schizonts eventually rupture (along with RBC) releasing more merozoites into the bloodstream (new cycle begins). This stage is where acute clinical symptoms appear.

Question 6

What fungal species most commonly causes human disease and what kind of infections does it cause (with examples)?

Answer 6

Candida albicans

Mucosal, e.g vulvovaginal candidiasis (thrush)
Systemic, e.g disseminated candidiasis

Question 7

What molecule do HIV viruses target and on which cells?

Answer 7

CD4 molecule on CD4 + T cells (interacts with CXCR4 co-receptor) and monocytes (CCR5 co-receptor).

Interaction between CD4 molecule and viral envelope glycoprotein gp120.

Question 8

What are viruses and how do they replicate?

Answer 8

Intracellular obligate parasites
Replicate using host-cell nuclear synthetic machinery
Divide by budding out of host cell or cytolysis

Question 9

Do viruses show host specificity?

Answer 9

Yes - but infect most other life forms, inc. bacteria

Question 10

List viral routes of infection

Answer 10

Faecal-oral, airborne, insect vectors, blood borne

Question 11

What makes HIV a retrovirus?

Answer 11

RNA used to make DNA via Reverse Transcriptase

Whereas normally in viruses DNA makes RNA which makes the protein

Question 12

Give an example of a virus

Answer 12

Smallpox (variola virus)

Question 13

What makes Prokaryotes more susceptible to the effects of a mutation?

Answer 13

They are haploid so if one gene is mutated, the effect will occur.
However in diploid cells, the mutation must be seen on both copies of DNA to occur.

Question 14

What is the main component of Prokaryotic cell walls?

Answer 14

Peptidoglycan

Question 15

How do Prokaryotes divide?

Answer 15

Binary fission

Question 16

What are the purpose of the pili (several pilus) on Prokaryotes?

Answer 16

They can have a role in movement, but are more often involved in adherence to surfaces, which facilitates infection, and is a key virulence characteristic.

Question 17

Give an example of a bacterial pathogen and it’s mode of transmission.

Answer 17

Shigella species
Faecal-oral route
Invades and destroys guts cells
Cell-to-cell spread using host actin

Question 18

What must be taken into consideration when making vaccines for Neisseria meningitidis?

Answer 18

Multiple serogroups - different sugar capsules

Vaccines must target the different serogroups

Question 19

Why are the mutation rates of viruses higher than humans?

Answer 19

They have half the point mutation rate as they have error prone replication and cannot deal with errors in genetic code efficiently.

Much shorter replication times

Question 20

What types of infection do fungi cause?

Answer 20

Cutaneous, mucosal and systemic

Question 21

What forms do yeast exist in?

Answer 21

Yeasts and filaments

Question 22

What are Protozoa and how do they replicate?

Answer 22

Unicellular eukaryotic organisms including blood, intestinal and tissue parasites
Replicate in the host by binary fission or trophozoite formation in cells

Question 23

How is a Protozoa infection acquired?

Answer 23

Ingestion

Vector transmission

Question 24

Compare malaria and leishmaniasis

Answer 24

Both caused by blood and tissue parasites -Plasmodium (malaria) and Leishmania species (Leishmaniasis)
Both replicate by trophozoite formation inside cells
Malaria transmitted via mosquito vector whereas leishmaniasis transmitted via sandfly vector

Question 25

What are helminths and how are they transmitted?

Answer 25

Metazoa with eukaryotic cells
Multicellular organism
Transmitted via fecal oral route

Question 26

Give examples of helminths

Answer 26

Flatworms (flukes), tapeworms and roundworms (e.g Ascaris)