<P> Hemolysis (from Greek "αιμόλυση" which means blood breakdown) is the breakdown of red blood cells . The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms . This is particularly useful in classifying streptococcal species . A substance that causes hemolysis is a hemolysin . </P> <P> When alpha hemolysis (α - hemolysis) is present, the agar under the colony is dark and greenish . Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha hemolysis . This is sometimes called green hemolysis because of the color change in the agar . Other synonymous terms are incomplete hemolysis and partial hemolysis . Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin producing the green oxidized derivative methemoglobin . </P>

When hemolysins are present on a blood agar plate they
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