Intracellular penetration and survival of Streptococcus pyogenes in respiratory epithelial cells in vitro.

Recurrence of pharyngotonsillitis caused by S. pyogenes after seemingly adequate antibiotic treatment has puzzled scientists for many years. We investigated the ability of S. pyogenes to invade HEp-2 cells and survive intracellularly. Five strains were tested, of which two were isolated from patients with recurrent pharyngotonsillitis, two without recurrent infection, while one was a reference strain. All five strains were found capable of penetrating the cells and surviving intracellularly for between 4 and 7 days. In this manner, an intracellular reservoir of bacteria was created, with the potential to cause recurrent infections.