Intracellularly invading Streptococcus pyogenes is degraded by autophagic machinery

Streptococcus pyogenes (also known as group A streptococcus, GAS) is the etiological agent for a diverse collection of human diseases ranging from self-limiting suppurative infections of the upper respiratory tract and skin to deeper and more serious invasive infections. Recent studies have revealed that it effectively attaches to and invades pharyngeal and skin epithelial cells. However, the fate of invading GAS into host cells has not clearly understood. We demonstrate that autophagy functions as another cellular degradation system for the intracellularly invading GAS. Intracellularly invading GAS was selectively acquired by the autophagosome-like compartments and degraded by fusion with lysosomes in non-phagocytic cells. In the autophagosome formation-deficient Atg5−/− cells, such compartments were not formed and the number of intracellular GAS markedly increased. Our results indicate that the autophagic machinery is not only for degradation of subcellular components, but also for a second security system against the intracellularly invading GAS.