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Fluid Tetrathionate Medium
An enrichment broth for isolation of Salmonellae from specimens suspected to be contaminated with Salmonellae in accordance with US Pharmacopoeia.
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Intended Use
Recommended as an enrichment broth for isolation of Salmonellae from specimens suspected to be contaminated with Salmonellae in accordance with U.S.P.
Composition
| Ingredients | g/L |
|---|---|
| Tryptone | 2.500 |
| Peptone | 2.500 |
| Bile salts | 1.000 |
| Calcium carbonate | 10.000 |
| Sodium thiosulphate | 30.000 |
Formula adjusted, standardized to suit performance parameters
Directions
Suspend 46.0 grams in 970 ml purified/distilled water. Heat just to boiling. DO NOT AUTOCLAVE. Cool to 45-50°C. On the day of use add 20 ml iodine solution (5 grams of potassium iodide and 6 grams of iodine in 20 ml distilled water) and 10 ml of 0.1% brilliant green solution. Mix well and dispense in 10 ml quantities. Do not heat after addition of iodine solution. Use the medium immediately after addition of iodine.
Note: Due to presence of Calcium Carbonate, the prepared medium forms opalescent solution with white precipitate.
Principle And Interpretation
Fluid Tetrathionate Medium was originally described by Mueller (1) and found that the medium selectively inhibit coliforms and permit unrestricted growth of enteric pathogens. The medium is now formulated according to FDA (2), United States Pharmacopoeia, 2019 (Vol. 5) (3), Compendium of Microbiological Examination of Foods (4) and Standard Methods for the Examination of Water and Wastewater (5) which specify this medium as enrichment medium for Salmonella species. Salmonella is the common causative agent of mild gastroenteritis to typhoid. It is common contaminant in food and other biological products. This medium supports the rejuvenation of Salmonella cells injured by food processing which are incapable of forming colonies on plate, but on injection can cause infection. This medium is recommended by USP for microbial limit tests for pharmaceutical preparations. Bile salts inhibit gram-positive microorganisms. The selectivity depends on the ability of thiosulphate and tetrathionate (formed by addition of Iodine and Potassium iodide) in combination to suppress commensal coliform organisms (6,7). The microorganism harbouring tetrathionate reductase flourish in this broth. Sodium thiosulphate forms the substrate for enzyme thiosulphate reductase. Sodium thiosulphates are also inactivators of halogens and can minimize its toxicity in the testing sample, if any during microbial limit tests. Tryptone and peptone supplies essential nutrients and vitamins in this medium. Calcium carbonate neutralizes the acidic tetrathionate decomposition products. Sodium chloride maintains osmotic balance.
Type of specimen
Pharmaceutical sample
Specimen Collection and Handling
For pharmaceutical samples, follow appropriate techniques for sample collection, processing as per guidelines (3) After use, contaminated materials must be sterilized by autoclaving before discarding.
Warning and Precautions
Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling specimens. Safety guidelines may be referred in individual safety data sheets.
Limitations
- For further confirmation, streak the enriched cultures after incubation, on plates of Brilliant Green Agar (M016), MacConkey Agar (M081) and Bismuth Sulphite Agar (M027).
Performance and Evaluation
Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at recommended temperature.
Quality Control
Appearance: White to cream homogeneous free flowing powder
Colour and Clarity of prepared medium: Complete medium with added brilliant green and iodine solution - Light green coloured opalescent solution with white precipitate, on standing the precipitate settles down.
Growth Promotion Test
As per United States Pharmacopoeia.
Cultural Response
Cultural characteristics observed with added brilliant green and iodine solution, after an incubation at 35-37°C for 18-24 hours, when sub cultured on MacConkey Agar (MU081) after enrichment in Tetrathionate medium.
| Organism | Inoculum (CFU) | Recovery | Colour of colony |
|---|---|---|---|
| Salmonella Abony NCTC 6017 (00029*) | 50-100 | good-luxuriant | colourless |
| Salmonella Typhimurium ATCC 14028 (00031*) | 50-100 | good-luxuriant | colourless |
| Salmonella Typhi ATCC 6539 | 50-100 | good-luxuriant | colourless |
| Escherichia coli ATCC 8739 (00012*) | 50-100 | little or no increase in numbers | white to pink with bile precipitate |
Key: *Corresponding WDCM numbers.
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and use freshly prepared medium. Use before expiry date on the label. On opening, product should be properly stored dry, after tightly capping the bottle in order to prevent lump formation due to the hygroscopic nature of the product. Improper storage of the product may lead to lump formation. Store in dry ventilated area protected from extremes of temperature and sources of ignition. Seal the container tightly after use. Product performance is best if used within stated expiry period.
Disposal
User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow established laboratory procedures in disposing of infectious materials and material that comes into contact with sample must be decontaminated and disposed of in accordance with current laboratory techniques (8,9).
| Product Name | Fluid Tetrathionate Medium |
|---|---|
| SKU | MU032 |
| Product Type | Regular |
| Physical Form | Powder |
| Origin | Animal |
| Packaging type | HDPE |
| References | 1. Cherry et al, 1972, Appl. Microbiol., 24:334 2.Hartman and Minich, 1981, J. Food and Prot., 44:385 3.Mueller, 1923, Compt. Rend. Sco. Biol., 89:434. 4.Salfinger Y., and Tortorello M.L. Fifth (Ed.), 2015, Compendium of Methods for the Microbiological Examination ofFoods, 5th Ed., American Public Health Association, Washington, D.C.5 Baird R.B., Eaton A.D., and Rice E.W., (Eds.), 2015, Standard Methods for the Examination of Water andWastewater, 23rd ed., APHA, Washington, D.C. 6.FDA Bacteriological Analytical Manual, 2005, 18th Ed., AOAC, Washington, DC. 7.Pollock M. R. and Knor R., 1943, Biochem J., 37:476. 8.MacFaddin J. F., 1985, Media for Isolation-Cultivation-Identification-Maintenance of Medical Bacteria, Vol. 1, Williamsand Wilkins, Baltimore. 9.American Public Health Association, Standard Methods for the Examination of Dairy Products, 1978, 14th Ed., WashingtonD.C.10.Isenberg, H.D. Clinical Microbiology Procedures Handb0ook. 2nd Edition. 11.Jorgensen,J.H., Pfaller , M.A., Carroll, K.C., Funke, G., Landry, M.L., Richter, S.S and Warnock., D.W. (2015)Manual of Clinical Microbiology, 11th Edition. Vol. 1. |
| Customized Product Available | No |
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