Table of Contents
In this blood agar composition and uses post we have briefly explained about blood agar principle, blood agar base composition, appearances, storage, preparation, result, applications, and limitations of blood agar base.
Blood Agar Base
The term “Blood Agar” isn’t a well-defined media. The term “blood agar” refers to an enhanced base medium that has been supplemented with defibrinated mammalian blood. Blood agar baser is made up of basic nutrients and 5% sheep blood.
Blood agar base can be used to cultivate fastidious organisms and to determine an organism’s hemolytic capabilities.
Hemolysins are exoenzymes produced by bacteria that lyse red blood cells and destroy haemoglobin. Hemolysins are produced by bacteria in various forms. Beta-hemolysin totally degrades red blood cells and haemoglobin. This clears a space around the bacterial colony.
β-hemolysis is the term used to describe such outcomes (beta hemolysis). Alpha-hemolysin partially degrades red blood cells, resulting in a greenish tint. α-hemolysis is the medical term for this (alpha hemolysis). The presence of biliverdin, a by-product of haemoglobin breakdown, is responsible for the greenish tint.
There will be no clearance if the organism does not create hemolysins or break down the blood cells. This is known as γ-hemolysis (gamma hemolysis).
Tryptone: 17.000, Soya peptone: 3.000, Sodium chloride: 5.000, Dextrose (Glucose): 2.500, Dipotassium hydrogen phosphate: 2.500, Agar: 15.000, 5% Sheep Blood. Combine the ingredients and adjust the pH to 7.3.
Prepare the required amount of TSA in a flask according to the directions on the dehydrated powder’s packaging.
If you’re using TSA broth powder, dissolve 20 g agar in 500 mL pure water. Before autoclaving, the medium should be heated and totally dissolved, with no powder on the vessel’s walls.
Autoclave for 20 minutes at 121°C. In a water bath, cool to 60°C. 5 percent defibrinated, sterile sheep blood (5 ml sheep blood can be added to 100 ml of agar).
Fill 15×100 mm Petri dishes with 20 mL. Allow for the solidification of the medium and the drying of the condensate. Place the plates in sterile plastic bags and keep them at 4°C until ready to use.
1. Decide whether the hemolysis is alpha, beta, or gamma. Streptococci culture as well as antimicrobial susceptibility testing (AST).
2. Streptococcus pneumoniae is presumptively identified using an optochin disc. Similarly, bacitracin discs (0.04U) were used to presumptively identify Streptococcus pyogenes.
3. To test for Streptococcus agalactiae using the CAMP method. To carry out a Haemophilus satellitism test.
4. Other than streptococci, blood agar base also used to isolate and cultivate Neisseria and other fastidious bacteria. Blood agar base can also be used to make antigens for Salmonella Typhi.
Alpha hemolysis (α)
The conversion of red blood cell haemoglobin to methemoglobin in the media around the colony is known as alpha hemolysis.The medium turns green or brown as a result of this. The colour is similar to “bruising” the cells.
Beta hemolysis (β)
The term “beta hemolysis” refers to the complete or genuine breakdown of red blood cells. The colony is surrounded by a clear zone that resembles the colour and transparency of the underlying medium. Several bacteria species produce toxic by-products that can harm red blood cells.
Gamma hemolysis (γ)
Gamma hemolysis (γ) is somewhat self-contradictory. Gamma indicates the lack of hemolysis. There should be no reaction in the surrounding medium.