Streptococcal M protein is a virulence factor for which group of bacteria?

Streptococcal M protein is a virulence factor for which group of bacteria?

• A. Group A Streptococcus
• B. Group B Streptococcus
• C. Staphylococcus aureus
• D. Escherichia coli

Answer: (A)

The main concept is that the M protein is a major virulence factor of Streptococcus pyogenes, the organism known as Group A Streptococcus. This surface protein helps the bacteria evade the immune system by inhibiting opsonization and phagocytosis, in part by binding host regulatory proteins like factor H and C4BP. Its high antigenic variability (many M types) allows the bacterium to dodge lasting immunity, contributing to persistent infections and post-infectious complications. In particular, antibodies against M protein can cross-react with heart tissue, linking GAS infections to rheumatic fever. Other bacteria listed rely on different virulence tools: Group B Streptococcus uses a protective capsule and other factors, Staphylococcus aureus relies on proteins like protein A and toxins, and Escherichia coli employs adhesins, toxins, and LPS. The specific association of M protein with Group A Streptococcus makes that choice the best fit.

The main concept is that the M protein is a major virulence factor of Streptococcus pyogenes, the organism known as Group A Streptococcus. This surface protein helps the bacteria evade the immune system by inhibiting opsonization and phagocytosis, in part by binding host regulatory proteins like factor H and C4BP. Its high antigenic variability (many M types) allows the bacterium to dodge lasting immunity, contributing to persistent infections and post-infectious complications. In particular, antibodies against M protein can cross-react with heart tissue, linking GAS infections to rheumatic fever.

Other bacteria listed rely on different virulence tools: Group B Streptococcus uses a protective capsule and other factors, Staphylococcus aureus relies on proteins like protein A and toxins, and Escherichia coli employs adhesins, toxins, and LPS. The specific association of M protein with Group A Streptococcus makes that choice the best fit.