Streptolysin O (SLO; slo), is a bacterial toxin that has four protein domains which is known to make the plasma membranes in animal cells permeable. It does this by creating pore complexes within the membrane by first binding a monomer to the cholesterol found in the target membrane and then forming an oligomeric transmembrane pore.[6] This toxin excreted by a Gram-positive bacteria Streptococcus pyogenes, under the classification of Thiol-activated cytolysin or CDCs.