What is this medium used for?
Fluid thioglycolate is a broth medium used for determining the oxygen requirements of a pure culture.
How is the oxygen requirement determined by using fluid thioglycolate broth?
After inoculation and incubation, the location of turbid growth reveals the oxygen requirements of the organism.
What is the content of this medium?
The medium contains the following ingredients.
- Pancreatic digest of casein 15 g/L
- Glucose 5.5 g/L
- Yeast extract 5/g/L
- Sodium chloride 2.5 g/L
- Sodium thioglycolate 0.5 g/L
- L cysteine 0.5 g/L
- Resazurin 1 mg/L
- Agar 0,75 g/L
Casein and glucose provide basic nutrients of sugar and amino acids. Yeast extract is a source of vitamins and growth factors to enrich the medium, as does the added cysteine. Sodium chloride helps maintain an osmotic balance in the medium. Thioglycolate is a chemical that acts as a reducing agent, an oxygen scavenger that enables the medium to remain anaerobic in the butt of the tube. The small amount of agar present acts as a thickening agent to reduce the speed with which oxygen can diffuse through the medium to re-oxygenate the butt of the tube. Resazurin is an indicator dye that is red in the presence of oxygen and colorless when in the absence of oxygen.
The result is a thickened broth medium that is aerobic at its surface and becomes increasingly more anaerobic as you go deeper into the tube. When autoclaved, all oxygen is driven out of the butt of the tube, and as it begins to diffuse back into the medium the portion of the broth at the top turns red, showing how far down oxygen has moved. As long as it is not shaken (which would trigger movement of oxygen throughout the medium), the medium is red/aerobic at the top and amber/anaerobic at the bottom.
How is the test performed?
For information on how to determine the oxygen requirements for microbes using fluid thioglycolate broth, refer to the “Oxygen Requirements Determination” test.