Final answer:
M protein is produced by bacteria, particular species of Streptococcus, and serves as a virulence factor to inhibit phagocytosis and evade the immune system.
Step-by-step explanation:
M protein is produced by bacteria, specifically by certain species of Streptococcus. M protein alters the surface of Streptococcus and inhibits phagocytosis, thereby evading the host's immune system. This virulence factor helps the bacteria to resist immune defenses by blocking the binding of complement molecules that would assist phagocytes in ingesting these bacterial pathogens. Understanding the function of M protein is important in the study of bacterial infections and their resistance mechanisms against the immune response.