Proteins M6 and F1 are required for efficient invasion of group A streptococci into cultured epithelial cells.

Group A streptococci were recently shown to be capable of invading human epithelial cell monolayers. Cell invasion might be an important virulence trait of streptococci that enable the pathogen to gain entry into deeper tissues after initial binding to host cells. Nothing is known concerning the nature of streptococcal components that mediate invasion. Using isogenic mutants of strain JRS4 that are defective in the expression of either M6 protein or protein F1, or both proteins, it was demonstrated that both adhesins are required for efficient invasion. Further more, expression of protein F1 on the surface of a non-invasive strain rendered the latter invasive, suggesting that protein F1 is directly involved in the invasion process.