Diabetic with unresolved skin lesion

[Oak]

A 52 year old diabetic patient reports to his physician's office complaining of an unresolved skin lesion on his foot. The lesion began several weeks ago as a blister and has since become a painful, erosive, expanding sore. On examination, the affected site is now 5 cm in diameter, with a black necrotic center and raised red edges. Which of the following toxins has a mechanism of action most similar to the toxin responsible for tissue damage in this patient?

A. Anthrax toxin
B. Botulinum toxin
C. Cholera toxin
D. Clostridium perfringens alpha toxin
E. Diphtheria toxin
F. Escherichia coli labile toxin
G. Pertussis toxin
H. Shigatoxin
I. Streptococcal erythrogenic toxins
J. Tetanus toxin
K. Toxic shock syndrome toxin-1

[kenneth masamaro]

Tough!I would go for Cl.perfringes alpha toxin.It was causing gas gangrene characterized by necrotizing ulcers??.Lets see how it goes.

[Oak]

You just missed it, the correct answer is E. This patient's wound is infected with Pseudomonas aeruginosa, and the characteristic lesion described is called ecthyma gangrenosum. The Pseudomonas alpha toxin, which is responsible for the tissue damage, inhibits protein synthesis by acting on EF-2 with a primary target cell in the liver. The diphtheria toxin has a similar action, although its target cells are heart and nerve.

Anthrax toxin (choice A) is an adenylate cyclase that causes fluid loss from cells.

Botulinum toxin (choice B) is a neurotoxin that decreases acetylcholine synthesis.

Cholera toxin (choice C) acts to increase adenylate cyclase activity by ribosylation of GTP-binding protein.

Clostridium perfringens alpha toxin (choice D) is a lecithinase.

Escherichia coli labile toxin (choice F) works in a fashion similar to the cholera toxin.

Pertussis toxin (choice G) causes fluid loss by ribosylating Gi.

Shigatoxin (choice H) decreases protein synthesis by inhibiting the 60S ribosomal subunit.

Streptococcal erythrogenic toxins (choice I) act similarly to the diphtheria toxin, but do so by increasing cytokine production.

Tetanus toxin (choice J) is a neurotoxin that inhibits the inhibitory neurotransmitters glycine and GABA.

TSST-1 (choice K) is a superantigen that acts by increasing cytokine production and decreasing liver clearance of endotoxin.