Fluid Thioglycollate Medium

Fluid Thioglycollate Medium (FTM) is used for the isolation and cultivation of aerobic and anaerobic organisms and is widely used in sterility testing applications. The addition of a small quantity of agar helps to retain the anaerobic conditions within the medium.  Fluid Thioglycollate Medium is used for sterility control of pharmaceutical products.

Fluid Thioglycollate Medium composition

Ingredientsg/L
Pancreatic Digest of Casein 15.0
Yeast Extract (Water-Soluble) 5.0
Dextrose Anhydrous5.0
Sodium Chloride2.5
L- Cystine0.5
Sodium Thioglycollate 0.5
Agar0.75
Sodium Solution (1 in 1000) Freshly prepared 1.0 mL
Fluid Thioglycollate Medium composition

Fluid Thioglycollate Medium Principle

Sodium thioglycollate is a reducing agent that removes molecular oxygen from the medium and prevents the accumulation of peroxides which may be lethal to some microorganisms. Sulfhydryl groups inactivate mercury and other heavy metals neutralizing the antibacterial effect of mercurial preservatives. A small amount of agar is added to impede the diffusion of oxygen.

Casein peptone and cystine supply nitrogen and carbon compounds that are necessary for the growth of aerobes and anaerobes. Sodium chloride is a source of essential electrolytes and maintains osmotic equilibrium. Resazurin is an oxidation-reduction indicator that turns pink when increased oxidation occurs.

Fluid Thioglycollate Medium Procedure

  • Suspend 29.0 grams of the medium in one liter of distilled water.
  • Mix well and dissolve by heating with frequent agitation.
  • Boil for one minute until complete dissolution. Dispense into appropriate containers and sterilize in autoclave at 121°C for 15 minutes.
  • The preferred medium should be stored at 2-8°C.
  • The color is clear amber with a pink upper layer. Cool before using and store in the dark.

The dehydrated medium should be homogeneous, free-flowing, and light beige. If there are any physical changes, discard the medium.

Once prepared it can be used sometime after preparation until it is 30% oxidized, which is indicated by a pink color on the Resazurinsurface. If the oxidation is greater, reheat the medium only once, with steam or boiling water, cool it, and use it.

Fluid Thioglycollate Medium Application and Interpretation

The broth medium should be equilibrated to room temperature before use. The surface of the containers, including the septum below the protective cap, is not sterile. Therefore, please be aware of the risk of secondary contamination due to handling. To reduce the risk of secondary contamination by defective glass containers or handling the following recommendations may be helpful:

  • Please control each single container for visible defects or turbidity. Do not use such containers.
  • Please avoid the contamination of culture media by contact with skin or body fluids. Such contaminated media cannot be used anymore.
  • In the case of negative pressure due to prior heat sterilization, the containers should be ventilated by sterile filter units before usage to avoid aspiration of potentially contaminated air.
  • The risk of transfer of microorganisms from the surface of the containers into the sterile culture medium can be minimized by disinfection of these surfaces followed by handling in sterile environments, e.g. isolators. The inoculation of the containers by sterile cannulas is safer than procedures that require the opening of media bottles or tubes.

Media that contain ingredients of animal or human origin such as meat extract must be considered potentially infectious. After contact with such media, disinfection of the affected skin area is recommended.

Strictly anaerobic microorganisms such as Clostridium sporogenes are growing in the lower, yellowish part of the broth medium. The growth of facultative anaerobic microorganisms such as Staphylococcus aureus is distributed in the complete broth medium. aerobic microorganisms such as Pseudomonas aeruginosa can grow in the upper, oxidized part of Fluid Thioglycollate Medium indicated by a slight pink color. Usually, the incubation is performed under aerobic conditions. Not more than the upper half of the the medium should have undergone a color change to pink, which is indicative of oxygen uptake at the end of the incubation period.

A Fluid Thioglycollate Medium is recommended for sterility testing of pharmaceutical products according to the European and US Pharmacopoeia. According to the Pharmacopoeia a membrane filtration method should be performed wherever possible, but also direct inoculation methods are possible.

Fluid Thioglycollate Medium Keynotes

For membrane filtration application, we recommend the use of our 100 mL Fluid Thioglycollate Medium or our 100 mL clear Fluid Thioglycollate Medium.

For direct inoculation, the amount of the inoculated sample material should not exceed 10% of the volume of Fluid Thioglycollate Medium. Fluid Thioglycollate Medium is incubated for 14 days at 30 to 35 °C and visually inspected for growth.

The sterility test is passed, if no growth is visible at the end of incubation.

It is recommended to identify grown microorganisms in order to find out the origin of contamination and to implement corrective actions.

Fluid Thioglycollate Medium Storage and Shelf life

The product can be used for tests until the expiry date if protected from light and properly sealed at +2 °C to +25 °C. The testing procedures as described on the CoA can be Started up to the expiry date printed on the label.

Fluid Thioglycollate Medium Quality Control

Control StrainsInoculum CFUIncubationExpected Results
Clostridium sporogenes10-10020-24 h at 33-35 °Cgood growth; pronounced turbidity
Staphylococcus aureus10-10020-24 h at 33-35 °Cgood growth; pronounced turbidity
Pseudomonas aeruginosa10-10020-24 h at 33-35 °Cgood growth; pronounced turbidity
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