Streptolysins are two homogenous exotoxins from Streptococcus pyogenes. Types include streptolysin O (SLO; slo), which is oxygen-labile, and streptolysin S (SLS; sagA), which is oxygen-stable.
SLO is part of the thiol-activated cytolysin family. It is hemolytically active only in a reversibly reduced state. It is antigenic, so its antibody antistreptolysin O can be detected in an antistreptolysin O titre.
SLS is stable in the presence of oxygen. It is not antigenic due to its small size. It is sometimes considered a bacteriocin due to similarities in the synthesis pathway.