This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
A 54-year-old diabetic patient complaints 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 toxin has a mechanism of action most similar to the toxin responsible for tissue damage in this patient? 
Select and explain. 
A. Anthrax toxin, B. Botulinum toxin, C. Cholera toxin, D. Diphtheria toxin
D: Diphtheria toxin
Answer: D: Diphtheria toxin 
Explanation: This is the history of ecthyma gangrenosum (skin infection) due to Pseudomonas aeruginosa. Exotoxin A of P. aeruginosa has a same mechanism of action as diphtheria toxin. Pseudomonas aeruginosa is a gram-negative bacterium, motile by polar flagella. It is catalase and oxidase test positive. It produces two impoant pigments: fluorecein and pyocyanin. Selective medium used for its isolation is ceimide agar.