A patient with erysipelas of the face. What is the causative microorganism?

Correct answer: B. Streptococcus pyogenes (beta-hemolytic)

• A. Pseudomonas causes infections in immunocompromised patients and burn victims — not erysipelas.
• B. Correct. Erysipelas is a superficial skin infection involving the upper dermis and superficial lymphatics caused by Streptococcus pyogenes (Group A beta-hemolytic streptococcus). It is characterized by a well-demarcated, raised, erythematous lesion.
• C. Staphylococcus aureus causes cellulitis and abscesses but is not the classic cause of erysipelas.
• D. Streptococcus viridans is associated with infective endocarditis and dental bacteremia — not erysipelas.