Hemolysis (microbiology)
The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms.
[1] Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells.
Streptolysin O is an oxygen-sensitive cytotoxin secreted by most Group A streptococcus (GAS) and Streptococcus dysgalactiae; it interacts with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), usually resulting in β-hemolysis under the surface of blood agar.
Streptolysin S is an oxygen-stable cytotoxin also produced by most GAS strains which results in clearing on the surface of blood agar.
The hemolysis of some weakly beta-hemolytic organisms is enhanced when streaked close to certain beta hemolytic strains of Staphylococcus aureus.
(left) α-hemolysis ( S. mitis );
(middle) β-hemolysis ( S. pyogenes );
(right) γ-hemolysis (non-hemolytic, S. salivarius )