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Microbiology

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Gram Positive Bacilli

Question
11 out of 71
 

The mechanism of action of the exotoxin produced by Corynebacterium diphtheriae can be characterized by which of the following? (AIPG 2009)



A Acting as a superantigen that binds to MHC class II protein and the T-cell receptor.

B Blocking the release of acetylcholine causing anticholinergic symptoms.

C Blocking the release of glycine (inhibitory neurotransmitter).

D Inhibits protein synthesis via EF-2 adenosine diphosphate (ADP) ribosylation.

Ans. D Inhibits protein synthesis via EF-2 adenosine diphosphate (ADP) ribosylation.

Category

Mechanism

Organism

Toxin

Toxins that stimulate

adenylate cyclase

Split NAD à attach ADP-R to regulatory protein

(G, or G, protein) à stimulate adenylate cyclase (directly or indirectly) à increase cAMP à cause hypersecretion.

Bacillus cereus

Bordetella pertussis

Clostridium perfringens

Escherichia coli (ETEC)

Vibrio cholerae

Enterotoxin

Pertussis toxin

Enterotoxin (hypothesized)

Labile toxin

Cholera toxin

Toxins that inactivate

elongation factor 2

Split NAD à attach ADP-R to EF-2 à halt protein

synthesis.

Corynebacterium diphtheriae

Pseudomonas aeruginosa

Diphtheria toxin

Pseudomonal exotoxin A

Toxins that inactivate

other host

enzymes

Split NAD à attach ADP-R to other host proteins

(precise target may be unknown) à inactivate

host protein.

Clostridium botulinum

C. perfringens

P. aeruginosa

Type C2 botulinum toxin

Iota toxin

Exoenzyme S

Toxins that Inhibit

respiration by

depleting NAD

Split NAD à no ADP-ribosylation à halt

respiration.

Yersinia pestis

Yersinia pseudotuberculosis

Murine toxin

Murine toxin

Inhibits protein synthesis via EF-2 adenosine diphosphate (ADP) ribosylation.

a. Diphtheriae produces a potent exotoxin encoded by a lysogenic beta-prophage. Following proteolytic cleavage, the A segment is released into the host cell where it inhibits only mammalian protein synthesis (ribosomal function) via ADP ribosylation of EF-2 which is a tRNA translocase.

b. Inhibition of protein synthesis disrupts normal cellular physiologic functions that are believed to be responsible for the necrotizing and neurotoxic effects of diphtheria toxin.

c. An exotoxin with a similar mode of action is produced by some Pseudomonas aeruginosa strains.

d. S. aureus is responsible for producing the toxic shock syndrome toxin that acts as a superantigen leading to T-cell activation.

e. Clostridium tetani toxin blocks the release of glycine, leading to "lock-jaw."

f. Clostridium botulinum toxin blocks the release of acetylcholine, causing central nervous system (CNS) paralysis and anticholinergic symptoms.

g. Finally, the heat-labile toxin produced by E. coli causes watery diarrhea by stimulating adenylate cyclase.

Gram Positive Bacilli Flashcard List

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