Streptolysin O is a labile toxin, and, with time, activity is irreversibly lost. The rate of activity loss is slowed by incubation with 0.1 M 2-mercaptoethanol or 0.01 M ethylenediaminetetraacetic acid (EDTA).
Streptolysin O, belongs to the group of thiol-activated toxins, 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.