Bacterial Pathogenesis

Question 0

How does virulence differ from pathogenicity?

Answer 0

Virulence is measurable

Question 1

Define virulence.

Answer 1

The relative capacity for a microbe to cause damage to the host.

Question 2

Name the 3 overarching bacterial virulence factors

Answer 2

Structural components (e.g. adherence factors; motility)
Ability of evade host defences (e.g. Antiphagocytic/-complement strategies)
Gene expression (e.g. Invasion factors; exotoxins/enzyme production)

Question 3

How does Streptococcus pneumoniae evade host defences?

Answer 3

The bacteria encapsulates itself preventing macrophages from accessing its receptors and thus avoids phagocytosis

Question 4

List 4 possible host immunity evasion mechanisms used by bacteria

Answer 4

Capsules
Detection avoidance
Damage to immune cells
Resistance to killing immune cells (avoiding action of lysing enzymes)

Question 5

By what mechanism do Pneumococcus, Meningococcus and Haemophilus evade the immune system?

Answer 5

Resistance to phagocytosis

Question 6

By what mechanism do Legionella, Mycobacterium and Taxoplasma evade the immune system?

Answer 6

Resistance to macrophage killing

Question 7

By what mechanism does Pseudomonas evade the immune system?

Answer 7

Secretes a leukotoxin to kill neutrophils

Question 8

By what mechanism does Clostridium difficile evade the immune system?

Answer 8

Makes itself inaccessible to the immune system by proliferating in the gut lumen.

Question 9

What type of bacterial toxin am I? I am:
Actively produced
Relatively unstable
Highly toxic
Synthesised by plasmids

Answer 9

I am an exotoxin!

Question 10

Do exotoxins directly or indirectly harm host cells?

Answer 10

Directly

Question 11

What type of toxin am I? I am: 
Released in bacterial death
Weakly toxic
Found in gram -ve cell walls
A lipopolysaccharide complex

Answer 11

I am an endotoxin!

Question 12

What 3 pathways can endotoxic activation take?

Answer 12

Activation of coagulation cascade
Release of prostaglandins and leukotrienes
Activation of the complement cascade

Question 13

What will likely result from endotoxic activation of the coagulation cascade?

Answer 13

Acute respiratory distress syndrome
OR
Disseminated intravascular coagulation

Question 14

What will likely result from endotoxic activation of prostaglandin and leukotriene release?

Answer 14

Endothelial damage and potential multi-organ failure

Question 15

What will result from endotoxic activation of the complement cascade?

Answer 15

IL-1 release and fever (normal inflammatory response)

Question 16

What does the tracheal cytotoxic Bordetella pertussis cause?

Answer 16

Whooping cough

Question 17

List the 4 mechanisms of action by which exotoxins can cause cellular injury

Answer 17

Cell or tissue degrading enzymes
Alter cell signalling pathways
Act as neurotoxins
Act as Superantigens

Question 18

What impact does a Superantigen have on the host?

Answer 18

It causes an excessive immune response activating a high number of T-cells, which activate large numbers of IFN-gamma, which activates macrophages, which over-produce pro-inflammatory cytokines IL1, IL-6 and TNF-alpha - can cause shock or multi-organ failure

Question 19

By which mechanism of action do Type I exotoxins function?

Answer 19

Disrupt the cell homeostasis by interfering with the cell membrane causing loss of ions and water. They act on the membrane from OUTSIDE the cell.

Question 20

By which mechanism of action do Type II exotoxins function?

Answer 20

One of two ways:

1) form pores in cell membrane, creating a channel and disrupting the membrane potential
2) destroy the integrity of membrane phospholipids by use of enzymes

Question 21

By which mechanism of action do Type III exotoxins function?

Answer 21

Interfere with host cell from WITHIN via two possible means:

1) injecting secretions into host cells via ‘secretion apparatus’
2) receptor-mediated endocytosis i.e. A-B toxins

Question 22

For A-B toxins which is the active component and which is the binding component?

Answer 22

A = Active
B = Binding

Question 23

Name 3 diseases caused by exotoxins from Gram -ve bacteria

Answer 23

Diarrhoea - E. coli (enterotoxin)
Cholera - Vibrio cholerae (enterotoxin)
Whooping cough - Bordetella pertussis (pertussis toxin)

Question 24

Name 3 diseases caused by exotoxins from Gram +ve bacteria

Answer 24

Pharyngeal diphtheria - Corynebacterium diphtheiae
Toxic shock or Scaled-skin syndrome - Staph. aureaus
Diarrhoea - Clostridium difficile (Toxin A)