Antiphagocytic M protein?

Antiphagocytic M protein?

• A. M protein
• B. Protein A
• C. Exotoxin A
• D. Panton-Valentine leukocidin

Answer: (A)

Antiphagocytosis is achieved by a surface protein that helps Streptococcus pyogenes dodge neutrophils and the complement system. The M protein is that key factor: it sits on the bacterial surface and, by interacting with host components, reduces opsonization and phagocytosis. It can recruit regulator proteins like factor H to the bacterial surface, dampening the complement cascade and decreasing C3b deposition, so neutrophils are less able to recognize and ingest the bacteria. It also can bind fibrinogen, which helps cloak the organism from phagocytes. The hyaluronic acid capsule adds to this shield, but M protein is the principal antiphagocytic determinant in this context. That’s why this option best fits the idea of an antiphagocytic factor. The other options are different types of virulence factors—for example, Protein A blocks Fc-mediated opsonization in Staphylococcus aureus, while the other two are toxins—so they don’t describe the antiphagocytic mechanism associated with M protein.

Antiphagocytosis is achieved by a surface protein that helps Streptococcus pyogenes dodge neutrophils and the complement system. The M protein is that key factor: it sits on the bacterial surface and, by interacting with host components, reduces opsonization and phagocytosis. It can recruit regulator proteins like factor H to the bacterial surface, dampening the complement cascade and decreasing C3b deposition, so neutrophils are less able to recognize and ingest the bacteria. It also can bind fibrinogen, which helps cloak the organism from phagocytes. The hyaluronic acid capsule adds to this shield, but M protein is the principal antiphagocytic determinant in this context.

That’s why this option best fits the idea of an antiphagocytic factor. The other options are different types of virulence factors—for example, Protein A blocks Fc-mediated opsonization in Staphylococcus aureus, while the other two are toxins—so they don’t describe the antiphagocytic mechanism associated with M protein.