Blood agar is an example of: March 2010

Ans. B: Enriched media A growth medium is considered differential if, when specific microbes are present, the medium or bacterial colonies themselves exhibit a color change that provides information about their identity. Blood agar (BAP) is a differential growth medium which is used to distinguish clinically significant bacteria from throat and sputum cultures. BAP contains 5% sheep blood. Ceain bacteria produce enzymes (hemolysins) that act on the red blood cells to lyse or break them down. Beta hemolysis means that the bacteria's hemolytic enzymes completely beak down the blood cells. The a-hemolysis pattern results in the media displaying clear halos around bacterial colonies. Alpha hemolysis (a-hemolysis) means that the bacterial enzymes only paially break down the blood cells. This results in the media showing a yellowish/greenish/brownish discoloration (like a bruise) around the colony, indicating incomplete hemolysis. Gamma hemolysis is essentially no hemolysis at all. The bacteria have no effect on the red blood cells, and there is no change to the color of the medium. Some of the terms for media are interchangeable. For example, the blood agar medium is an enriched medium but bacteria lysing red cells show a clearing around their colonies. Thus, it is an differential medium as well.