Microbial Toxin

Question 1

Which toxin facilitate spread of microbes through tissues?

Answer 1

Hayluronidase
Collagenase
Elastase
Deoxyribonuclease
Streptokinase

Question 2

Which toxin damage cellular membrane?

Answer 2

1. Cytolysin - damage cells
   - -> Hemolysin - detectable action on erythrocytes
2. Lecithinase - degrade cell membrane

Question 3

Toxin stimulate cytokine production?

Answer 3

Pyrogenic exotoxin (type of Superantigen)

1. erythrogenic toxin (Strep pyogene)
2. TSST-1 (Staph aureus)

Question 4

Effect of Superantigen on immune system?

Answer 4

Binding MHC II and T-cell receptor –> activate large T-cell numbers –> excessive production cytokine

Question 5

Toxin inhibit protein synthesis?

Answer 5

1. Diphtheria toxin & Pseudomonas aeruginosa Exotoxion A –> inactivate elongation factor 2
2. Shiga toxins of Shigella dysteriae and E. coli

Question 6

Mechanism of Exotoxin A?

Answer 6

ADP ribosyltransferases, transfering ADP-ribose from nicotinamide adenin dinucleotide (NAD) to diphthamide (modified histine) –> inactive EF-2 in cytoplasm

Question 7

Mechanism of Shiga toxin?

Answer 7

RNA N-glycosidases –> remove adenine from 28S RNA (60S ribosomal subunit) –> inactivate ribosome

Question 8

Toxin modify intracellular signalling pathway?

Answer 8

1. Heat-labile enterotoxins Vibrio cholerae and E. coli
2. Pertussis toxin
3. Heat-stable enterotoxin I of E. coli
4. Anthrax edema factor & adenylate cyclase toxin
5. Anthrax lethal factor
6. Toxin A & B of Clostridium difficile

Question 9

Mechanism of Vibrio cholerae & E. coli heat-labile enterotoxin?

Answer 9

ADP ribosyltransferases –> activate alpha-subunit of Gs (GPCR) –> increase cAMP –> active chloride secretion –> diarrhea

Question 10

Mechanism Pertussis toxin?

Answer 10

ADP ribosyltransferase –> inactivate alpha-subunit Gi –> increase cAMP

Question 11

Mechanism heat-stable enterotoxin E. coli?

Answer 11

activate guanylate cyclase –> increase cGMP enterocyte –> diarrhea

Question 12

Mechanism anthrax edema factor & adenylate cyclase toxin?

Answer 12

Adenylate cyclases –> increase cAMP

Require: activation by calmodulin and calcium

Question 13

Anthrax lethal factor?

Answer 13

Endopeptidase cleaves MAP kinase –> inactivate

Question 14

Toxin A & B C. diff?

Answer 14

glycosyl transferase alter actin cytoskeleton

* transfer glucose from UDP-glycose to Rho family GTPases –> inactivate Rho, Rac, Cdc42

Question 15

Toxins inhibit relase neurotransmitter?

Answer 15

1. Botulinum toxin

2. Tetanus toxin

Question 16

Botulinum toxin?

Answer 16

Zinc-dependent endopeptidase inactivate SNARE proteins for neuroexocytosis
–> inhibit release acetylcholine at myoneural junctions

Question 17

Usage of botulinum toxin?

Answer 17

Usage: treat focal dystonias and involuntary movement disorders

Question 18

Tetanus toxin?

Answer 18

Zn-depedent endopeptidase –> SNARE inactivation –> decrease neuroexocytosis
–> inhibit release neurotransmitter from inhibitory interneurons in spinal cord

Question 19

Intracellular toxin entry to cell?

Answer 19

1. bi-functional domains (A= active & B = binding)
2. Bind normal cell receptor
3. Endocytosis entry