streptolysins

Streptolysins are exotoxins produced by some Streptococcus species, most notably Streptococcus pyogenes (group A streptococcus). These toxins are cytolytic proteins that disrupt host cell membranes and contribute to tissue damage during infection. The two best characterized streptolysins are streptolysin O and streptolysin S.

Streptolysin O (SLO) is an oxygen-labile, cholesterol-dependent cytolysin. It binds to cholesterol in host cell membranes and forms pores, leading to cell lysis. SLO activity is enhanced in reducing environments and can be inhibited by cholesterol. It is antigenic and elicits an immune response, which underpins the use of anti-streptolysin O antibodies (ASO) as a historical marker of recent streptococcal infection. SLO is associated with several disease processes, including tissue necrosis and systemic manifestations in invasive streptococcal diseases.

Streptolysin S (SLS) is an oxygen-stable, non-immunogenic cytolysin that also disrupts cell membranes, contributing to cytotoxicity and tissue damage. SLS is primarily responsible for the characteristic beta-hemolysis observed around Streptococcus pyogenes colonies on blood agar and is produced by the sag gene cluster. Unlike SLO, SLS is not readily inhibited by cholesterol and is active under a broader range of conditions.

Together, streptolysins enhance streptococcal virulence by lysing host cells, modulating immune responses, and promoting bacterial spread. Laboratory detection often centers on SLO antibodies for past infection, while SLS contributes to hemolysis patterns used in bacterial identification.