Capsular hyaluronic acid of group A streptococci hampers their invasion into human pharyngeal epithelial cells.

Group A streptococci (GAS) cause various diseases, from uncomplicated noninvasive, to severe invasive infections. Capsular hyaluronic acid (HA) is known to resist phagocytosis, however, interaction between HA and epithelial cells have not been clearly understood. In this study, both HA-producing wild strains and HA-nonproducing mutants were employed to examine their invasiveness into confluent cultures of HEp-2, a nonphagocytic human epithelial cell line. Invasion of HEp-2 cells by GAS strains increased over time. The hasA gene encoding hyaluronate synthase of GAS strains was inactivated by allelic replacement. It was found that hasA-inactivated mutants were internalized into HEp-2 cells more efficiently than their parent strains under various conditions in terms of incubation time and inoculum size. Taken together, these findings indicate that GAS can be internalized into HEp-2 cells with considerably high frequencies and that the presence of HA of GAS decreased the invasion efficiency.