Blood agar is an enriched, bacterial growth medium. Fastidious organisms, such as streptococci, do not grow well on ordinary growth media. Blood agar is a type of growth medium that encourages the growth of bacteria, such as streptococci, that otherwise wouldn’t grow well at all on other types of media. Blood Agar consists of a base containing a protein source (e.g. Tryptones), Soybean protein digest, Sodium chloride (Nacl), agar and 5% sheep blood.

Pancreatic digest of casein

Papaic digest of soy meal

NaCl

Agar

Distilled water

Combine the ingredients and adjust the pH to 7.3. Boil to dissolve the agar, and sterilize by autoclaving.

Procedure for the preparation of Blood Agar

Prepare the Blood Agar base as instructed by the manufacturer. Sterilize by autoclaving at 121oC for 15 minutes. Transfer thus prepared Blood Agar base to a 50oC water bath. When the agar base is cooled to 50oC, add sterile blood agar aseptically and mix well gently. Avoid formation of air bubbles. You must have warmed the Blood to room temperature at the time of dispensing to molten agar base. (Note: If you are planning to prepare a batch of Blood Agar plates, prepare few blood agar plates first to ensure that Blood is sterile). Dispense 15 ml amounts to sterile petri plates aseptically Label the medium with the date of preparation and give it a batch number (if necessary). Store the plates at 2-8 oC, preferably in sealed plastic bags to prevent loss of moisture. The shelf life of thus prepared Blood Agar is up to four weeks.

Blood Agar :

Prepare Trypticase Soya Agar (TSA). Sterilize it by autoclaving (121 degree Celsius/ 15psi/ 20-30 minutes).

Cool down the sterilized culture media to around 50 degree Celsius.

Add 5% (ie 5 ml to 100 ml TSA) fresh defebrinated ( which is not clotted) sheep blood under aseptic conditions.

Mix gently and dispense on petriplates immediately. Take care that media doesn't solidify during dispensing.