Which virulence factor is primarily responsible for adherence to host tissues in Streptococcus pyogenes?

• A. M protein
• B. Streptolysin O
• C. Hyaluronic acid capsule
• D. C5a peptidase

Answer: (A)

Streptococcus pyogenes relies on a surface protein called M protein as its main adhesion factor. This protein acts as an adhesin, allowing the bacterium to attach to epithelial cells and extracellular matrix components, which facilitates colonization of the throat and other tissues. At the same time, M protein helps the bacteria resist phagocytosis by interacting with host factors that dampen the complement system, aiding survival in the host. Other virulence factors have different roles: Streptolysin O is a toxin that lyses cells, the hyaluronic acid capsule mainly helps evade the immune system by concealing the bacterium, and C5a peptidase reduces neutrophil recruitment. So the adherence to host tissues is best explained by the M protein.