Erysipelas, a superficial skin infection with a sharply demarcated, raised border, is most classically caused by which organism?

Erysipelas is classically caused by group A beta-hemolytic Streptococcus (Streptococcus pyogenes), producing a sharply demarcated, raised, erythematous lesion confined to the upper dermis/superficial lymphatics — distinguishing it from cellulitis, which has a less distinct border and a broader range of causative organisms.