<prompt> 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 childs infection from phagocytosis and provides serologic specificity?Erythrogenic toxinHyaluronic acidLipoteichoic acidM protein  <response>: Streptococcus pyogenes, or Group A Streptococcus GAS, produces a number of virulence factors. The M protein d is the organisms most important antiphagocytic factor, and it conveys serologic specificity-over 100 serotypes are now known. In the early stages of growth, the bacteria have hyaluronic acid b capsules. This capsule similar to human hyaluronic acid structure is rapidly destroyed by the organisms own hyaluronidase. Also known as spreading factor, hyaluronidase plays a role in GAS cellulitis. Erythrogenic toxin a is a superantigen produced by some strain of GAS lysogenized by a bacteriophage carrying the toxin gene; it causes the rash of scarlet fever. A second superantigen, streptococcal pyrogenic toxin, causes streptococcal toxic shock syndrome. Streptolysin O e an oxygen-labile hemolysin is useful for identification of the organism and is antigenic so antistreptolysin antibodies can be used to diagnosis rheumatic fever, a sequelae of GAS infection. Lipoteichoic acid c is a component of the cell wall that is involved in binding of the bacterium to host fibronectin. 