11+12 Microorganisms in disease

Question 1

Define pathogenicity and list the four requirements for it:

Answer 1

The capacity of a micro-organism to cause an infection.

Transmissibility, establishment in/on a host, harmful effects, persistence.

Question 2

Define virulence.

Answer 2

Degree to which a micro-organism is able to cause disease.

Question 3

Define infectivity.

What are the two factors for this?

Answer 3

The ability of a micro-organism to become established in/on a host.

Microbial ligand and host cell surface receptor.

Question 4

What are the ligand-receptor interactions behind E.coli, S.pyogenes and influenza?

Answer 4

E.coli: fimbriae: glycolipids on uroepithelial cells
S.pyogenes: protein-F:fibronectin
Flu: haemagglutinin: respiratory epithelial sialic acid receptors.

Question 5

What are virulence factors?

Answer 5

Components of micro-organisms resulting in harmful effects.

Question 6

What is endotoxin?

Answer 6

Component of g-ve cell wall (E.coli, N.meningitidis).
Released from damaged/dead cells.
Active component is lipopolysaccharide (LPS).

Question 7

What is the host response to endotoxin?

3 routes.

Answer 7

Systemic inflammatory response syndrome. All uncontrolled:
T cell response.
Clotting cascade: DIC.
Complement activation.

Question 8

How does N.meningitidis result in gangrenous digit loss?

Answer 8

Endotoxin mediated increase in vascular permeability. Loss of protein, fluid and plasma into tissues. Compensatory vasoconstriction -> gangrene.

Question 9

What are exotoxins?

Examples:

Answer 9

Proteins produced by living bacteria.

Botulin. Tetanospasmin.

Question 10

Botulism organism + route?
How does it work?
Effects? (5)

Answer 10

Clostridium botulinum. Contaminated food/dirty wound.
Binds to presynaptic ACh vesicles.
Diplopia, dysphasia, dysarthria, dry mouth, death from respiratory failure.

Question 11

Tetanus organism + route?
How does it work?
Effect?

Answer 11

Clostridium tetani. Wound infection.
Tetanospasmin produced with spore germination. Binds to synapses. Inhibits release of inhibitory neurotransmitters in CNS.
Death by respiratory paralysis.

Question 12

Name some exotoxin mediated infections. (7)

Answer 12

Cholera. 
Diphtheria. 
C.diff.
E.col O157 - verotoxin.
Staph scalded skin syndrome (epidermolysin).
Whooping cough (pertussis).
Scarlett fever (strep.pyogenes).

Question 13

Name the virulence factors that S. pyogenes makes: (7)

Answer 13

Hyaluronidase and streptokinase (break down connective tissue).
C5a peptidase.
Streptolysins O + H (lyse R/WBCs + platelets).
Erythrogenic toxin (scarlet fever).
Toxic shock syndrome toxin.

Question 14

Which bacteria inhibit phagocytosis and how? (2)

Answer 14

S.pyogenes: M-protein binds fibrinogen masking its surface.

S.pneumoniae: polysaccharide capsule inhibits opsonisation.

Question 15

Which microbes evade the immune system by being intracellular pathogens?

Answer 15

Mycobacterium tuberculosis.
Salmonella typhi.
Listeria monocytogenes.

Question 16

How do T cells respond to endotoxins?
3 chemicals,
5 effects.

Answer 16

TNF-α, γ-interferon, IL-1 release

Fever, rigors, hypotension, tachycardia, collapse.

Question 17

Which exotoxin does each of these produce:
E.col O157
Staph scalded skin syndrome

Answer 17

E.coli: verotoxin.

Staph: epidermolysin.