A 38-year-old fishmonger presents with a 5-day history of a well-demarcated, violaceous plaque on the dorsum of his right hand and index finger following a puncture wound from a fish bone 2 days prior. The lesion has central clearing, advances slowly at the periphery, and stops at the wrist. He reports mild burning pain and stiffness but denies fever, lymphangitis, or regional lymphadenopathy. The structure marked **B** in the diagram represents the characteristic presentation of erysipeloid. Which of the following is the MOST APPROPRIATE initial antimicrobial therapy for this condition?
A. Penicillin V or amoxicillin orally
B. Cephalexin orally
C. Clindamycin intravenously
D. Vancomycin intravenously
Explanation
Why Penicillin V or amoxicillin orally is right
The lesion marked B is erysipeloid caused by Erysipelothrix rhusiopathiae, a gram-positive rod acquired through occupational exposure to contaminated animal products (fish, meat). The classic presentation—sharply demarcated violaceous plaque with central clearing, slow centrifugal spread, localized to the hand, and absence of systemic toxicity—is pathognomonic. Penicillin (or amoxicillin) is the gold standard treatment for localized erysipeloid. Critically, E. rhusiopathiae is intrinsically resistant to vancomycin, a common empiric choice for skin infections, which would result in clinical failure if used (Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases 9e).
Why each distractor is wrong
Vancomycin intravenously: Although vancomycin is often used empirically for gram-positive skin infections, Erysipelothrix rhusiopathiae is intrinsically vancomycin-resistant. Using vancomycin would be ineffective and delay appropriate therapy, risking progression to the diffuse or septicemic forms (particularly endocarditis with aortic valve involvement).
Cephalexin orally: First-generation cephalosporins are not reliably active against E. rhusiopathiae. While some third-generation cephalosporins (e.g., ceftriaxone) are alternatives, cephalexin is not recommended as first-line therapy for this organism.
Clindamycin intravenously: Clindamycin has poor activity against E. rhusiopathiae and is not recommended. The organism's susceptibility to clindamycin is unpredictable, and it is not a standard or alternative agent for erysipeloid.
High-YieldNEET PG
Erysipelothrix rhusiopathiae (erysipeloid) = violaceous hand plaque in fish/meat handlers + intrinsic vancomycin resistance → treat with penicillin, not vancomycin.
Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases 9e
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