M Protein-Associated Adherence of Streptococcus pyogenes to Epithelial Surfaces: Prerequisite for Virulence

Virulent strains of Streptococcus pyogenes containing M protein were found to adhere well to human cheek epithelial cells in vitro, whereas an avirulent M − mutant strain adhered feebly. Pretreatment of M + strains with trypsin to remove their M protein surface coating or reacting them with type-specific antiserum markedly impaired their abilities to attach to epithelial cells. Electron microscopy revealed that the attachment of an M + strain to germfree rat epithelial cells was mediated by a fuzzy surface structure previously shown to contain M protein. When mixtures of streptomycin-resistant M + and M − strains were introduced into the mouths of mice, the proportions of the M + strain increased on tongue and cheek surfaces relative to its M − mutant. These data indicate that the surface fuzz of S. pyogenes which contains M protein functions in the attachment of the organism to epithelial surfaces, thereby permitting its colonization.