bacterial toxins

Question 1

toxins

Answer 1

there’s a huge diversity of toxins

loads of different bacteria produce toxins. They have different mechanisms of action. They act on different cell types and they act on different targets within cells.

• you can roughly split them into non-protein toxins and protein toxins

Question 2

non protein toxins

Answer 2

endotoxin; embedded in the cell surface

and the term endotoxin is specific for lipopolysaccharide, which is in the outer membrane of gram-negative bacteria.

You do have other bacterial cell wall components that can have the same effect of endotoxin e.g lipoteichoic acid and phosphatidylglycerol

Question 3

mycolactone - non protein toxin

Answer 3

The only other non-protein toxin that’s been characterized is something called mycolactone and this is a polyketide derived drug molecule and this is produced by some mycobacteria.
- this toxin is responsible for this disease called buruli ulcer, which is where you get Progressive necrosis on the skin.
- So you get this necrosis due to the toxin causing tissue damage, but actually the bacteria remain localized So actually it’s very Superficial on the surface,
- this disease isn’t really seen outside the tropics but it’s recently been registered as an emerging disease in West Africa.

Question 4

protein toxins

Answer 4

there’s three different types of protein toxins
- huge diversity and they’ve just been roughly divided into three groups
○ type 1 type 2 type 3.
- So the protein toxins are known as exotoxins because these get released from the bacterial cell.

Question 5

endotoxin characteristics

Answer 5

chemical nature: lipopolysaccharide
relationship to cell: part of outer membrane
denatured by boiling: no
antigenic: yes
form toxoid: No
potency: relatively low (<100 micrograms)
specificity: low degree
enzymatic activity: no
pyrogenicity: yes

Question 6

exotoxin characteristics

Answer 6

chemical nature: protein
relationship to cell: extracellular, diffusible
denatured by boiling: usually
antigenic: yes
form toxoid: yes - important in vaccines
potency: relatively high (1 micrograms)
specificity: high degree
enzymatic activity: usually
pyrogenicity: occasionally

Question 7

the inflammatory response

Answer 7

endotoxin triggers inflammation that can lead to septic shock
inflammatory response involves 4 main events:
- vasodilation
- activation of endothelial cells
- increased vascular permeability
- chemotactic factors

brought out by combination of complement activation, cytokine release, monocyte and PMN transmigration/ activation

Question 8

inflammatory response - activation of endothelial cells

Answer 8

It makes them sticky so neutrophils and other cells start to stick to them and that helps with them starting to move out of the blood vessels into tissues

Question 9

inflammatory response - increased vascular permeability

Answer 9

This helps neutrophils squeeze through the gaps between the endothelial cells and also helps things like complement move out of the bloodstream into the tissue

Question 10

inflammatory response - chemotactic factors

Answer 10

drive the neutrophils macrophages et cetera to the site of infection and obviously complement factors play a key role with chemotaxis

Question 11

symptoms of inflammation

Answer 11

you get heat with inflammation and that’s due to the increased blood flow to the area

Get redness

Then you start to get swelling and the swelling is due to a buildup of fluid in the area.

pain is due to pressure on nerve ending

then eventually you get loss of control and that can be devastating if it’s this systemic inflammation.

Question 12

stages of septic shock

Answer 12

1. systemic inflammatory response syndrome
2. sepsis
3. severe sepsis
4. septic shock

Question 13

1st stage of septic shock - systemic inflammatory response syndrome

Answer 13

• temperature over 38 or less than 36
• higher than normal respiratory rate
• usually high neutrophil count
• mild hypotension

all of this can be brought about by one thing which is endotoxin

Question 14

septic shock - stage 2 (sepsis)

Answer 14

SIRS with proof bacteria in bloodstream

Question 15

sepic shock - sever sepsis - stage 3

Answer 15

• multiple organ dysfunction
• dramatic hypotension - the fluid is moving out of the bloodstream into the tissues

Question 16

septic shock - stage 4

Answer 16

• hypotension despite fluid administration
• disseminated intravascular coagulation
• acute respiratory distress
• multiple organ failure and death

Question 17

relationship between bacterial endotoxin structure, function and biological activity

Answer 17

in terms of variability, there’s a very low variability of lipid A between different bacteria.

No variability of the diphosphate

and then as you move out you get more and more variability. - O antigen variability high

in terms of endotoxin activity. It’s the lipid a component that causes the activity
- so the lipid a is essential because that’s integral within the bacterial membrane.
-the lipid A is a component within the outer membrane, that’s somehow got to be released for it to have an effect -So it’s due to lysis of the bacteria that you get this effect of endotoxins

Question 18

structure of bacterial endotoxin (LPS)

Answer 18

O - antigen
core polysaccharide
disaccharide diphosphate
lipid A
fatty acids

Question 19

how does endotoxin trigger septic shock (1)

Answer 19

• You get bacterial lysis, so that will release the LPS and then that gets Bound in the serum by LPS binding protein.
• they form a complex and then that Bind to the receptor cd14 on phagocytes
• Once cd14 is associated with LPS and LPS binding protein that triggers TLR 4 to start signalling Pathways, and that causes cytokine release
• And then that’s what has the effect.
  if it is all localized. It’s no problem and is beneficial to fight an infection but it’s when it happens systematically It’s an issue.

Question 20

septic shock - activation of complement pathway (2)

Answer 20

• So All of this in the release of acute phase proteins cause activation of complement Cascade- you get production of prostaglandins and leukotrienes- and you also get activation of the coagulation Cascade
  
  • and in terms of symptoms you start to see acute respiratory distress syndrome due to activation of the coagulation Cascade and you get this disseminated intravascular coagulation.
    so you start to get endothelial damage and then that might lead to multiple organ failure

Question 21

exotoxins - cytotoxins

Answer 21

attack a variety of cell types
- toxins that attach specific cell types include: neurotoxin, leuokotoxin, hepatotoxin, cardiotoxin

Question 22

exotoxins - cholera toxin

Answer 22

produced by vibrio cholerae

Question 23

exotoxins - shiga toxin

Answer 23

produced by shigella species

Question 24

exotoxin - diptheria toxin

Answer 24

produced by corynebacterium diptheriae

Question 25

exotoxin - tetanus toxin

Answer 25

produced by clostridium tetani

Question 26

exotoxin - adenylate cyclase

Answer 26

toxin produced by bordatella pertussis cause of whooping cough

Question 27

exotoxin - phospholipase

Answer 27

toxin produced by clostridium perfringens cause of gangrene

Question 28

exotoxin - enterotoxin

Answer 28

protein toxins that cause diarrhea or vomiting

Question 29

exotoxins - type 1

Answer 29

superantigens - toxins that get released from a bacterial cell, They bind to host cell surfaces, but they don’t go into the host cells.
- antigen-independent activation of T cells
- inappropriate activation of IL-2 -> toxic shock

symptoms identical to septic shock. It’s just been induced by a different mechanism.

Question 30

exotoxins - type 2 toxins

Answer 30

pore-forming, phospholipase
- destroy the integrity of the mammalian cell cytoplasmic membrane

Question 31

exotoxins - type 3 toxins

Answer 31

A-B toxins
- have a B portion comprising a translocation (T) domain and a receptor binding domain (R)
- have an enzymatic portion (A) that acts on some intracellular host protein

Question 32

how do type 1 toxins work

Answer 32

super antigens bind indiscriminately to MHC Class 2 and CD4 T cell receptors and forms a link between the two that doesn’t require an antigen to be present.
- So this means now that almost any CD4 T cell can become activated - It doesn’t have to have the right receptor
- so you get up to one in five T cells can be activated in this way.
- this then causes the clonal expansion of the huge diversity of CD4 T-cells and a huge diversity of receptors and you get an unfocused immune response
- you get an excess production of cytokines and then that leads to systemic Inflammatory response and you get toxic shock.

Question 33

normal antigens mechanism

Answer 33

normally when an antigen presenting cell like a macrophage expresses an antigen on the surface for recognition by CD4 T-cells, it presents that antigen on MHC Class 2.
- And so then that gets recognized by CD4 T cells that have the specific receptor for that antigen
- , so then those CD4 T cells become activated and they start to proliferate and you get the production of cytokines.
- So when this happens normally it’s only the CD4 cells with the right receptor for that antigen - so it’s about one in 10,000 CD4 T-cells that becomes activated.

Question 34

examples of superantigen - toxic shock syndrome toxin-1

Answer 34

• superantigen produced by some strains of staphylococcus aureus
• causes toxic shock syndrome

Question 35

examples of superantigen - staphyloccal enterotxins

Answer 35

• superantigens produced by some strains of staphylococcus aureus
• cause food poisoning

Question 36

examples of superantigen - streptococcal pyrogenic exotoxin

Answer 36

• produced by group A streptococci
• causes toxic shock-like syndrome

Question 37

type 2 toxins action - pore-forming toxins

Answer 37

• insert into host cell membranes And they form a pore in the membrane.
• That pore causes an ion imbalance because of the difference in osmolarity.
• So ions rush out, water rushes in and the cell bursts.
• the pore-forming toxins usually associate with cholesterol in the cell membrane

a big difference between the cell membrane of bacteria And host cells is the presence of cholesterol in the host cells so that’s why they’re specific for the host cell membranes and don’t affect their own membranes.

Question 38

type 2 toxins actions - phospholipase

Answer 38

• they cleave the phospholipids in the bilayer.
• they disrupt the membrane and that causes membrane damage and can cause the cell to lyse

Question 39

exmaples of type 2. toxins - pore forming

Answer 39

staphylococcal alpha-toxin
- produced by staphylococcus aureus
- pore-forming cytolysin

listeriolysin
- produced by listeria monocytogenes
- pore-forming membrane damaging toxin, role in mediating escape from phagosome

pneumolysin
- produced by streptococcus pneumoniae
- pore forming cytolysin
- induction of inflammation in lung
- inhibits cilial beat in respiratory mucosa

Question 40

exmaples of type 2. toxins - phospholipase

Answer 40

clostridium perfringens alpha toxin
- causes gas gangrene
- demonecrotic and hemolytic
- is a zinc metallophospholipase C

Question 41

gas gangrene

Answer 41

results from toxin and gas production during anaerobic fermentation

Question 42

type 3 toxins types

Answer 42

• simple A-B toxin
• compound A-B toxin