SHEEP BLOOD AGAR PLATE

Sheep Blood Agar medium is both differential and enriched medium and used for the isolation, cultivation and detection of hemolytic activity of fastidious microorganisms like Streptococci and Pneumococci. The Blood Agar plate medium contains highly nutritious extract and the 5 % blood supplement which provides additional use in isolation, cultivation, and determination of hemolytic reactions of fastidious pathogenic microorganisms. Hemolytic patterns may vary with the source of animal blood or type of base medium used. In sheep blood, nucleotidase destroys V factors preventing the growth of Haemophilus species on sheep blood agar unless other microorganisms, such as Staphylococci, provide the V factors. Small amounts of reducing sugars inhibit the expression of ?-hemolysis, and ?-hemolytic Streptococci may develop a green zone or ring of hemolysis.
A number of streptococcal species produce substances that lyse the red cell wall releasing hemoglobin. Such substances are referred to as hemolysins. The activity of streptococcal hemolysins, streptolysins, can be readily observed when the organisms are growing on a blood agar plate. Different Streptococci produce different effects on the red blood cells in blood agar.
? Those that achieve incomplete hemolysis and only partial destruction of the cells around colonies are called alpha-hemolytic Streptococci. Characteristically, this type of hemolysis is seen as a distinct greening of the agar in the hemolytic zone, and thus this group of streptococci has also been referred to as the viridans group.
? Species whose hemolysins cause complete destruction of red cells in the agar zones surrounding their colonies are said to be beta-hemolytic and are represented as small opaque or semi translucent colonies surrounded by clear zones in a red opaque medium. Two types of beta lysins are produced; Streptolysin-O, an antigenic oxygen-labile enzyme and Streptolysin-S, a non-antigenic oxygen-stable enzyme. The hemolytic reaction is enhanced when blood agar plates are streaked and simultaneously stabbed to show subsurface hemolysis by Streptolysin-O in an environment with reduced oxygen tension. Some strains of Staphylococcus, Escherichia coli, and other bacteria also may show beta hemolysis.
? Some species of Streptococci do not produce hemolysins. Therefore, when their colonies grow on blood agar, no change is seen in the red blood cells around them. These species are referred to as nonhemolytic or gamma hemolytic Streptococci.

For cultivation of fastidious organisms and studying haemolytic reactions.