Bacterial Toxins

Question 1

Endotoxin definition

Answer 1

Present on the outside of a bacteria. Can shed in vesicles or released when the bacteria dies

Question 2

Exotoxin defintion

Answer 2

Produced inside the cell and secreted out of the bacteria

Question 3

What is a bacterial toxin

Answer 3

A poison produced/expressed by a bacteria

Question 4

Can toxins have enzymatic activity

Answer 4

Yes

Question 5

Why could antibiotics be harmful in toxin-producing bacteria infections? (endotoxin)

Answer 5

More toxins can be relased from the bacteria once it has been lysed/killed by the antibiotic, increasing effects from the toxin

Question 6

Endotoxins - gram neg or pos?

Answer 6

Gram neg as its located in the LPS but also Listeria have endotoxin

Question 7

Can endotoxin have systemic effects?

Answer 7

Yes - bacterial sepsis
- systemic inflammatory response 
- cytokines 
- nitric oxide
- fever
- hypotension 
- intravascular coagulation 
- organ failure 
All can lead to septic shock

Question 8

What are OMVs? Key roles?

Answer 8

Outer membrane vesicles.

Contain LPS roles in cell stress, gaining nutrients and pathogenesis, can contain exotoxins

Question 9

Direct mechanisms to affect target cells:

Answer 9

• Help spread through tissue with hyaluronidase
• Damage cell membranes/structures with collagenase
• Immunomodulatory IgA protease
• Inhibit protein synthesis
• Inhibit neurotransmitter release

Question 10

Correct match:
Type I toxin: A-B toxins. Translocate active enzymatic component to target cell to modify target molecule
Type II toxin: bind to surface receptors, not translocated into host, stimulate transmembrane signals
Type III toxin: act directly on cell membranes

Answer 10

Type I toxins: bind to surface receptors, not translocated into host, stimulate transmembrane signals
Type II toxins: act directly on cell membranes
Type III toxins: A-B toxins. Translocate active enzymatic component to target cell to modify target molecule

Question 11

Why are Type II toxins called AB toxins?

Answer 11

They have an active (A) and a binding (B) component(s)

Question 12

What does the A component do?

Answer 12

Toxic component that attacks the host structure/function. Has an effect on the host

Question 13

What does the B component do?

Answer 13

Binds to the host cell receptor

Question 14

Place in order the timeline of AB toxins:

• AB dissociates
• A enters the cytoplasm and has effect. B is removed by exocytosis
• Exocytosis - vacuole becomes acidified and membrane breaks down
• Endocytosis

Answer 14

1) Endocytosis
2) Exocytosis - vacuole becomes acidified and membrane breaks down
3) AB dissociates
4) A enters the cytoplasm and has effect. B is removed by exocytosis

Question 15

Describe AB toxins

Answer 15

• Single gene
• Single protein
• A linked to B by disulphide bond
  Example: Diptheria, Tetanus toxins

Question 16

Describe AB5 toxins

Answer 16

• Several genes
• 1 A, 5 Bs
• Separate subunits covalently linked
• B subunits can be the same or different
  Example: Cholera identical Bs, Pertussis 4 different Bs

Question 17

Advantage of some AB5 toxins having different B subunits

Answer 17

Allows the microbe to bind to different host cell receptors and have different effects

Question 18

Describe 2A:7B toxins

Answer 18

• 2 A components: lethal and oedema factors
• 7 B components can be protective antigens
• Assembles on cell surface
  Example: Anthrax

Question 19

Which toxin ADP-ribosylates?

Answer 19

AB (exo)toxin

• Cholera: Gs protein (cAMP activation)
• E.coli: Gs protein (cAMP activation)
• Pertussis: Gi protein (Prevents cAMP deactivation)
• Diptheria: Elongation factor 2 (Stops protein synthesis)
• Pseudomonas A: Elongation factor 2 (stops protein synthesis)