Bacterial exotoxins- Lecture 20

Question 1

Stages of Infection

Answer 1

Colonization and entry into host cells, evade the immune system and damage the host

Question 2

Patterns of pathogenesis

Answer 2

(1) produce investable toxins
(2) proliferate at mucous membranes and inject effectors (toxins) into the host cell
(3) Evade the immune system to live inside cells
(4) Enter cells and release toxins inside

Question 3

Primary mechanisms of adhesion

Answer 3

Adhesion are proteins found on the tips of pili
also, use T6SS to inject effectors to mediate uptake

Question 4

Ways of penetrating the mucous membranes

Answer 4

(1) direct uptake into epithelial cells
(2) Transverse M cells to mediate being eventually uptake into M cells

Question 5

How are M cells transversed by bacteria?

Answer 5

(1) Use a section system, i.e. (T3SS) to generate membrane ruffling
(2) Use cell-damaging proteins to enter cells and subsequently enter nearby cells (epithelial cells)

Question 6

How does Shigella enter M cells?

Answer 6

(1) Enters into M cells
(2) Macrophages engulf the shigella
(3) pathogen is released from macrophages and has broken mucous membrane giving ability to infect epithelial cells

Question 7

Exotoxins

Answer 7

Typically secreted upon lysis of bacteria into the surrounding fluid, toxins that can be effective with or without the pathogen present

Question 8

Targets of exotoxins

Answer 8

(1) Neurotoxins: Neurons and nervous system
(2) cytotoxins: organs throughout the body
(3) Enterotoxins: gastrointestinal toxins

Question 9

How does the immune system react to toxins?

Answer 9

produces antibodies, but may be too slow to react to fast-acting toxins

Question 10

Toxoid

Answer 10

Used for vaccines, a non-toxic version of the toxin that is highly antigenic

Question 11

Classes of toxins

Answer 11

(1) AB toxins: B subunit mediates entry of the A subunit (toxin)
(2) Hemolysins: includes phospholipase, pore-forming and detergent toxins
(3) Superantigens: causes over-activation of the immune system and cytokine storms, since it leads to over-recruitment of T-cells

Question 12

Botulinum toxin

Answer 12

(1) A neurotoxin that causes paralysis, produced by Clostridium botulinum under anaerobic conditions (i.e., canned foods), heat-labile so heating is insufficient
(2) Toxin enters cells through receptor-mediated endocytosis
(3) Acidification of the Endsome triggers the release of A subunit
(4) A subunit (peptidase) cleaves SNARE proteins, prevents exocytosis of vesicles that carry neurotransmitters, blocks acetylcholine release from pre-synaptic nerves and prevents innervation of muscle tissue

Question 13

What activity does the A subunit of botulinum toxin have?

Answer 13

Peptidase activity, cleaves SNARE proteins

Question 14

Tetanospasmin toxin

Answer 14

Neurotoxin produced by Clostridium tetani, Enters neurons in muscles through receptor-mediated endocytosis, travels back to CNS through retrograde axonal flow from motor neurons to the spinal cord

Cleaves SNARE proteins in inhibitory neurons usually lead to suppression of involuntary muscle contractions but SNARE cleavage prevents exocytosis of vesicles, resulting in continuous muscle contraction

Question 15

Cholera toxin

Answer 15

Enterotoxin AB, produced by Vibrio Cholera (aquatic bacteria), the toxin is produced following colonization of intestinal epithelial and adherence using pili

Entry into cells: the five B subunits bind microvilli receptors on enterocytes, creating portal for A subunit entry

ADP-ribosyltransferase (A subunit) transfers the ADP-ribose group to the G-proteins, keeps it on indefinitely, leads to overproduction of CAMP, turns off CFTR (cystic fibrosis transmembrane conductance regulators), causes loss of water and ions from infected enterocytes leads to watery diarrhea

Question 16

Self-limiting infections

Answer 16

if host hydrates well enough they can survive without the use of antibiotics since the pathogen cannot survive for a long-time inside the host

Question 17

Anthrax

Answer 17

AB cytotoxin produced by bacillus anthracis, spore-forming bacteria, lies dormant until access to epidermis, lung or intestinal tissue, produces two virulence plasmids pOX1 and pOX2

Question 18

pXO1 plasmid activity

Answer 18

(Anthrax toxin) contains B-Subunit: protective antigen, and A-subunit: edema factor and lethal factor

B subunit binds anthrax toxin receptor, monomer B Is cleaved by Furin (protease) to produce heptamer that allows for A-subunit receptor-mediated endocytosis

B-subunit forms pores in the end-some following acidification

Edema factor: adenyl cyclase, increases CAMP levels leading to loss of water and ions

Lethal factor: metalloprotease, inactivates mitogen-activated protein kinase kinases, kinases are essential for cell growth leads to apoptosis

Question 19

Diphtheria toxin

Answer 19

Produced by Corynebacterium diphtheria, infects the throat and releases the exotoxin, mild sore throat and fever lead to malaise and fatigue

Toxin leads to tissue destruction after some time leads to a whiteish and gray appearance of tonsils

ADP-ribosyltransferase halts translation in specific tissues

Question 20

How does the Diphtheria toxin halt protein translation

Answer 20

B-subunit binds to heparin-binding epidermal growth factor receptor, triggers receptor-mediated endocytosis

Endocytosis followed by acidification of the endsome stimulates proteolytic processing of the A subunit, (cleaves key disulphide bond) and releases catalytic domain into the cell

A subunit targets translation elongation factor 2 (ETF 2), required for polypeptide elongation during translation

A subunit (ADP-ribosyltransferase) adds ADP-ribose group to EF2 to inactivate it

Question 21

Gas Gangrene

Answer 21

Membrane-degrading phospholipase enters open wounds and germinates when the environment is sufficiently anaerobic enough to produce a toxin

Toxin Is a metallophospholipase, with similar activity to phospholipase C (hydrolysis of head groups of phospholipids) and required zinc for activity

Produces diacylglycerol as a product of lysis, can act downstream activating cell pathways: arachidonic acid and thromboxane A2, resulting in tissue damage (Edema) and swelling

Causes muscle tissue breakdown and gas ferments amino acids and muscle glycogen which causes infection to spread quickly and no specific antibiotics or vaccines are available.