This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gram-Negative Infections - Pseudomonal Infections, Subject name: Skin
Ecthyma gangrenosum is caused by? 
Select and explain. 
A. Fungal infection, B. Pseudomonas aeruginosa, C. Staphylococcus, D. Streptococcus
B: Pseudomonas aeruginosa
Answer: B: Pseudomonas aeruginosa 
Explanation: ANSWER: (B) Pseudomonas aeruginosaREF: Dermatology by jean bolognia 2nd e p. 1093"Ecthyma gangrenosum is caused by pseudomonas aeruginosa'"Ecthyma gangrenosum is an infection of the skin typically caused by Pseudomonas aeruginosa. It presents as a round or oval lesion,1 cm to 15 cm in diameter, with a halo of erythema. A necrotic center is usually present with a surrounding erythematous edge, representing where the organism invaded blood vessels and caused infarctions. These ulceritic lesions are single or multiple and heal with scar formation. The mechanism of tissue destruction is Pseudomonas exotoxin A"