Final answer:
Blood agar is enriched with 5% sheep blood and used to grow and differentiate hemolytic bacteria like Streptococcus and Listeria, with the presence of hemolysis indicated by the clear zones around colonies.
Step-by-step explanation:
The type of agar made by adding blood to the medium before autoclaving is known as blood agar. Blood agar is a rich growth medium that contains tryptic soy agar enriched with 5% sheep blood, although blood from other animals may also be used. This type of agar supports the growth of many bacteria and is particularly used for the detection and differentiation of hemolytic bacteria, such as Streptococcus and Listeria. The presence of hemolysis can be observed through the clearing of the red blood cells around colonies on the agar, indicating the lysis of blood by the bacteria. This characteristic helps in the diagnosis of certain bacterial infections. For instance, the clear zone around small grayish colonies on sheep blood agar can suggest Listeria infection, reflecting a serious condition that requires appropriate medical treatment, such as antibiotics, depending on the pathogen identified.