contains chemicals that inhibit or halt(slow down) the growth of some organisms. Other organisms have enzyme systems that allow them to deal with the selective agents
Differential media
contain chemicals that produce visible differences among different groups of organisms when grown on that medium. such as color or changes in the appearence.
7%aNaCl is a selective medium
present an osmotir pressure that is too eextreme for many bacteria to survive
Hemolysis
break down of red blood cells - change of blood agar surrouding the colonies.
3 Hemolytic abilities
1. Beta hemolysis - complete hymolysis. Cleared agar around the colonies.
2. Alpha hemolysis - partial hemolysis. Agar around the colinies look greenish but not clear.
3. Negative hemolysis - no Hemolysis has accoured.