L1 - Bacterial pathogens and disease 1 (Exotoxins)

Question 1

What is a pathogen?

Answer 1

A microorganism that is capable of causing disease

Question 2

What is pathogenicity?

Answer 2

The ability of an infectious agent to cause disease

Question 3

What is virulence?

Answer 3

The quantitative ability of an agent to cause disease

Question 4

What is toxigenicity?

Answer 4

The ability of a microorganism to produce a toxin that contributes to the development of disease

Question 5

What are exotoxins?

Answer 5

heterogeneous group of proteins produced and secreted by living bacterial cells.

They are produced by both gram positive and gram negative bacteria

Question 6

What advantages to exotoxins give to bacteria?

Answer 6

• evade the immune response (escape from phagocytosis)
• enable biofilm formation
• enable attachment to host cells

Question 7

What toxins are produced by Staphylococcus aureus?

Answer 7

• Hemolytic toxins:
  cause cells to lyse by forming pores

important cuase of features of the S.aureus disease

alpha, beta, gamma toxins

• Phenol Soluble modulins:
  aggregate the lipid bilayer of host cells - lysis

Question 8

Describe the genetics of exotoxins?

Answer 8

many toxins are encoded by extrachromosomal genes:

• plasmids
• lysogenic bacteriopahge

Question 9

What are the classification of Exotoxins?

Answer 9

• membrane acting toxins - type 1
• membrane damaging toxins - type 2
• Intracellular toxins - type 3

Question 10

Describe the activity, interference and target of Membrane acting toxins type 1?

Answer 10

• they act from outside the cell
• interfere with host cell signalling by inappropriate activation of host cell receptors
• target receptors include:

Guanylyl cyclase (increase intracellular cGMP)

Adenyl cyclase (increase intracellular cAMP)

Rho proteins

Ras proteins

Question 11

Describe the activity of membrane damaging toxins?

Answer 11

The cause damage to the host cell membrane (either receptor mediated or receptor independant) :

• insert channels into host cell membrane

(Beta sheet toxins, alpha helix toxins)

• enzymatical damage (PSM)

Question 12

What is the difference between receptor mediated and receptor independant membrane damaging toxins?

Answer 12

receptor mediated:
- toxin binds to receptor and causes the formation of another pore/channel

receptor independant:
- toxin attaches to membrane and causes disintergration

Question 13

Describe the activity of intracellular toxins type 3 and what the A subunit consists of?

Answer 13

• active within the host cell
• usually 2 components: AB toxins

receptor binding and translocation function (B)

toxigenic/enzymatic (A)
There may be multiple or single B subunits

A subunit:

• may have ADP - ribosomal transferases
• glucosyltransferases
• deamidase
• protease
• adenylcyclase

Question 14

How are toxins inactivated and what are they called when done so?

Answer 14

can be inactivated by using formaldehyde or glutaraldehyde

inactivated toxins are called toxoids

Question 15

Give examples of vaccines where toxoids are the base?

Answer 15

tetanus vaccine
diphtheria
pertussis