Streptolysin O causes both lysis of cells and cardiotoxicity. Streptolysin O is widely used for the controlled permeabilization of cell membranes. Streptolysin O exists in two forms, a reduced active state and an oxidized reversibly inactive state .

When streptococci secrete streptococcal hemolysin O, it is in an active state, but it will quickly oxidize into a reversible inactive state and form disulfide bonds[2]. Streptolysin O is a secreted virulence factor of GAS that induces apoptosis in neutrophils and macrophages at later time points (~4 h). Streptolysin O induces eukaryotic cell lysis in a cholesterol-dependent manner, is highly upregulated in the GAS M1T1 clone during bloodstream dissemination. Streptolysin O is known to promote Group A Streptococcus (GAS) resistance to phagocytic clearance by neutrophils, a critical first element of host defense against invasive bacterial infection[3].