Intracellular Staphylococcus aureus employs the cysteine protease staphopain A to induce host cell death in epithelial cells

Staphylococcus aureusis a major human pathogen, which can invade and survive in non-professional and professional phagocytes. Intracellularity is thought to contribute to pathogenicity and persistence of the bacterium. Upon internalization by epithelial cells, cytotoxicS. aureusstrains can escape from the phagosome, replicate in the cytosol and induce host cell death. Here, we identified a staphylococcal cysteine protease to induce cell death by intracellularS. aureusafter translocation into the host cell cytoplasm. We demonstrated that loss of staphopain A function leads to delayed onset of host cell death and prolonged intracellular replication ofS. aureusin epithelial cells. Overexpression of staphopain A in a non-cytotoxic strain facilitated intracellular killing of the host cell even in the absence of detectable intracellular replication. Moreover, staphopain A contributed to efficient colonization of the lung in a mouse pneumonia model. Our study suggests that staphopain A is utilized byS. aureusto mediate escape from the host cell and thus contributes to tissue destruction and dissemination of infection.Author SummaryStaphylococcus aureusis a well-known antibiotic-resistant pathogen that emerges in hospital and community settings and can cause a variety of diseases ranging from skin abscesses to lung inflammation and blood poisoning. The bacterium asymptomatically colonizes the upper respiratory tract and skin of about one third of the human population and takes advantage of opportune conditions, like immunodeficiency or breached barriers, to cause infection. AlthoughS. aureusis not regarded as a professional intracellular bacterium, it can be internalized by human cells and subsequently exit the host cells by induction of cell death, which is considered to cause tissue destruction and spread of infection. The bacterial virulence factors and underlying molecular mechanisms involved in the intracellular lifestyle ofS. aureusremain largely unknown. We identified a bacterial cysteine protease to contribute to host cell death mediated by intracellularS. aureus. Staphopain A induced killing of the host cell after translocation of the pathogen into the cell cytosol, while bacterial proliferation was not required. Further, the protease enhanced survival of the pathogen during lung infection. These findings reveal a novel, intracellular role for the bacterial protease staphopain A.