A child attending classes in a preschool is noted by his teacher to have several skin lesions on his arms. The lesions are pustular in appearance and some have broken down and are covered with a yellow crust. Which of the following protects the most likely etiologic agent of this child's infection from phagocytosis and provides serologic specificity?
Erythrogenic toxin Hyaluronic acid Lipoteichoic acid M protein