Question

What is hemolysis? How do you test the hemolytic activity of certain bacteria? What kind of hemolytic activity do you know?

Answer 1

Hemolysis is the breakdown of red blood cell, releasing hemoglobin. Thus, hemolysis is destruction of red blood cells in blood.

Hemolytic activity of bacteria is tested by culturing the bacteria on blood agar plate. This plate has medium containing sheep blood. Bacteria produce exoenzymes called hemolysin that will cleave red blood cells. There are different kinds of hemolysins produced by bacteria. Beta hemolysins cleave red blood cells and hemoglobin completely. Hence, these colonies will have a clear zone around them (beta hemolysis). Alpha hemolysin producing bacteria partially cleave red blood cells. Hence, a greenish zone is seen around the colonies (alpha hemolysis). No clearing will be seen if the bacteria cannot produce hemolysin (gamma hemolysis).

Group A streptococci like Streptococcus pyogenes is beta hemolytic due to production of streptolysin O and streptolysin A. Streptococcus pneumoniae and streptococcus viridans are alpha hemolytic bacteria while Enterobacter faecalis is gamma hemolytic.