Triple Sugar Saline Iron Agar

 

In 1940, Sulkin, Willett, and Hajna described a triple-sugar ferrous sulphate medium for the identification of enteric bacteria. Triple Sugar Iron (TSI) Agar is used for the presumptive identification of Enterobacteriaceae based on the fermentation of carbohydrates and the production of gas and H2S. Triple Sugar Iron Agar contains three carbohydrates: glucose (dextrose), lactose, and sucrose.

Triple Sugar Iron Agar is a differential medium that contains lactose, sucrose, a small amount of glucose (dextrose), ferrous sulphate, and the pH indicator phenol red. If an organism can ferment any of the three sugars present in the medium, the medium will turn yellow. If an organism can only ferment dextrose, the organism consumes a small amount of dextrose in the medium within the first ten hours of incubation. After that time, the reaction that produced acid reverses in the aerobic areas of the slant, and the medium in those areas turns red, indicating alkaline conditions. 

The anaerobic areas of the slant, such as the butt, will remain yellow and not revert to an alkaline state. This happens with Salmonella and Shigella. Sodium thiosulfate in the medium is reduced by some bacteria to hydrogen sulphide (H2S), and the latter reacts with ferric ions in the medium to produce iron sulphide, a black, insoluble precipitate.

Result Interpretation On Triple Sugar Saline Iron Agar

If the bacteria only use glucose, the bottom turns yellow and the slope turns red.

If the bacteria use glucose, sucrose, and/or lactose, the bottom and slope will turn yellow.

Bacteria do not use any of the sugars. The bacteria will consume the peptones in this case. The slope and pellet will be red if the bacteria can metabolize peptones both aerobically and anaerobically. If peptones can only be metabolized aerobically, the slope turns red and the base remains unchanged.

The division (detachment) of the agar detects the production of gas (CO2 and O2).

The presence of the black precipitate indicates that the bacteria were able to generate hydrogen sulfide (H2S) from sodium thiosulfate. As H2S is colourless, ferric ammonium citrate is used as an indicator of insoluble ferrous sulphide formation.

Composition Of Triple Sugar Saline Iron Agar

Ingredients

Gms/Ltr

Peptic digest of animal tissue

20.00

Meat extract

3.00

Yeast Extract

3.00

Sodium chloride

30.00

Lactose

10.00

Sucrose

10.00

Glucose

1.00

Ferric citrate

0.30

Phenol red

0.024

Sodium thiosulfate

0.30

Agar

15.00

TM Media Manufacturer of Culture Media

To save microbiologists time and ensure accurate results, TM Media has manufactured Culture Media in both Dehydrated and Ready-to-use forms. Ready-to-Use Media is available in plates, bottles, bags, and tubes as slants.

TM Media is a one-stop solution for all the Culture Media needs. As with over 2000 variants of Dehydrated Culture Media, TM Media offers Culture Media and Biological Media Bases with animal or non-animal origin.

For more, visit www.tmmedia.in.

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