Which organism is commonly linked to erysipelas?

• A. Streptococcus pneumoniae
• B. Streptococcus pyogenes
• C. Staphylococcus aureus
• D. Staphylococcus epidermidis

Answer: (B)

Erysipelas is a superficial bacterial skin infection that is most classically caused by Streptococcus pyogenes, a Group A Streptococcus. This organism infects the upper dermis and superficial lymphatics, producing a rapidly enlarging, well-demarcated, raised red plaque often on the face or legs. Its virulence factors, such as M protein and enzymes like hyaluronidase, facilitate spread in skin tissue and lymphatics, which explains the sharp borders that distinguish erysipelas from more diffuse cellulitis. While Staphylococcus aureus can cause skin infections, it typically produces non-demarcated cellulitis or abscesses rather than the raised, clearly defined lesions seen with erysipelas, and Staphylococcus epidermidis is more associated with device-related infections. Streptococcus pneumoniae is mainly a respiratory pathogen, not a common cause of erysipelas.