Blood Agar (BA)

🩸 Blood Agar Interactive Microbiology Learning System

Intended Use

Blood Agar (BA) is an enriched, differential medium used for isolation of many clinically important bacteria and demonstration of hemolysis.

Principle

• 5% sheep blood enriches growth.
• Hemolysins produce characteristic hemolysis.

Composition

Component	Role
Tryptic Soy/Columbia Base	Nutrients
5% Defibrinated Sheep Blood	Growth factors & hemolysis
Agar	Solidifying agent

Preparation

1. Prepare basal medium.
2. Autoclave 121°C for 15 min.
3. Cool to 45–50°C.
4. Add sterile 5% sheep blood gently.
5. Pour plates.

Interpret Colonies

Organism	Expected
Streptococcus pyogenes ATCC 19615	β-hemolysis
Streptococcus pneumoniae ATCC 49619	α-hemolysis
Enterococcus faecalis ATCC 29212	γ-hemolysis

• Not selective.
• Hemolysis depends on incubation.
• Further identification tests are required.

1. Bailey & Scott.
2. Koneman.
3. MacFaddin.
4. CLSI M22.