noun, plural: streptolysins
A streptolysin is a hemolytic exotoxin produced by or derived from certain strains of streptococci. The streptococci are Gram-positive bacteria that occur in chains of varying lengths. Many of them are known to release toxins, such as streptolysins and erythrogenic toxins. While alpha-hemolytic streptococci cause incomplete hemolysis, beta-haemolytic streptococci (of which Streptococcus pyogenes is an example) can cause complete hemolysis of red blood cells. They produce a broad zone of haemolysis on blood agar as a result of streptolysin O and S release.
Two forms of streptolysin occur: streptolysin O, which is oxygen-labile and streptolysin S, which is oxygen-stable. In 1930s, E. W. Todd was able to identify these two toxins responsible for the ability of group A streptococcus to lyse the red blood cells of mammals.1 Streptolysin O is immunogenic, which means it can incite certain immune cells to produce antibodies against it. Sreptolysin S is not immunogenic perhaps due to its relatively smaller size. Also, streptolysin S is oxygen-stable, which means that it is stable in the presence of atmospheric oxygen.
Word origin: strepto- from Streptococcus + (hemo)lysin)
1 Wessels, M. R. (2005). Streptolysin S. The Journal of Infectious Diseases, 192 (1): 13–15. https://doi.org/10.1086/430625