This is a differential medium. It is a rich, complex medium that contains 5% sheep red blood cells. BAP tests the ability of an organism to produce hemolysins, enzymes that damage/lyse red blood cells (erythrocytes). The degree of hemolysis by these hemolysins is helpful in differentiating members of the genera Staphylococcus, Streptococcus and Enterococcus.
Beta-hemolysis is complete hemolysis. It is characterized by a clear (transparent) zone surrounding the colonies. Staphylococcus aureus, Streptococcus pyogenes and Streptococcus agalactiae are b-hemolytic (the picture on the left below shows the beta-hemolysis of S. pyogenes).
Partial hemolysis is termed alpha-hemolysis. Colonies typically are surrounded by a green, opaque zone. Streptococcus pneumoniae and Streptococcus mitis are a-hemolytic (the picture on the right below shows the a-hemolysis of S. mitis).
If no hemolysis occurs, this is termed gamma-hemolysis. There are no notable zones around the colonies. Staphylococcus epidermidis is gamma-