What causes the triple sugar iron agar to turn red?

The meagre amount of acid production in the slant of the tube during glucose fermentation oxidizes rapidly, causing the medium to remain orange red or revert to an alkaline pH.

What are the three sugars in triple sugar iron agar?

TSI Agar contains three carbohydrates dextrose, lactose and sucrose. A color change from a reddish salmon to a pale yellow indicates carbohydrate fermentation; this acid production is detected by the Phenol Red pH indicator.

What are the three sugars in TSI Agar slants?

TSI Agar contains three sugars (dextrose, lactose and sucrose), phenol red for detecting carbohydrate fermentation, and ferrous sulfate for detection of hydrogen sulfide production (indicated by blackening in the butt of the tube).

What is indicated by the formation of a black precipitate in a tube of triple sugar iron TSI medium?

The black precipitate indicates that the bacteria were able to produce hydrogen sulfide (H2S) from sodium thiosulfate. Because H2S is colorless, ferric ammonium citrate is used as an indicator resulting in the formation of insoluble ferrous sulfide.

Which is the correct interpretation of a tube of triple sugar iron TSI medium that develops a red slant and red butt?

If the medium in the butt of the tube becomes yellow (acidic), but the medium in the slant becomes red (alkaline), the organism being tested only ferments dextrose (glucose). A yellow (acidic) color in the slant and butt indicates that the organism being tested ferments dextrose, lactose and/or sucrose.

What does triple sugar iron agar contain?

Triple sugar iron agar (TSI) is a differential medium that contains lactose, sucrose, a small amount of glucose (dextrose), ferrous sulfate, and the pH indicator phenol red.

Which three things are tested for by the triple sugar iron test?

Triple Sugar Iron. TSI agar tests organisms for 3 things: (1) carbohydrate fermentation (2) gas production, and (3) hydrogen sulfide production. Carbohydrate fermentation: TSI slants contain three carbohydrates: glucose (0.1%), sucrose (1%), and lactose (1.0%), as well as phenol red (pH indicator) and peptones.

Is TSI Agar selective or differential?

Triple sugar iron agar (TSI) is a differential medium that contains lactose, sucrose, a small amount of glucose (dextrose), ferrous sulfate, and the pH indicator phenol red. It is used to differentiate enterics based on the ability to reduce sulfur and ferment carbohydrates.

What do you need to know about triple sugar iron agar?

Welcome to Microbugz. Triple Sugar Iron Agar. Triple sugar iron agar (TSI) is a differential medium that contains lactose, sucrose, a small amount of glucose (dextrose), ferrous sulfate, and the pH indicator phenol red.

How to test for triple sugar iron ( TSI )?

Procedure for Triple Sugar Iron Agar (TSI) Test With a sterilized straight inoculation needle touch the top of a well-isolated colony Inoculate TSI Agar by first stabbing through the center of the medium to the bottom of the tube and then streaking on the surface of the agar slant.

How is triple sugar iron used as a differential medium?

see Difco Manual, 9th Ed, (1953) pp. 166-168 (Table on p. 161.) Triple Sugar Iron medium is a differential medium that can distinguish between a number of Gram-negative enteric bacteria based on their physiological ability (or lack thereof) to: The medium contains 1.0% each of sucrose and lactose and 0.1% glucose.

Why are the butt and slant of iron agar yellow?

The slant will remain red 1.0 % lactose/1.0% sucrose: If lactose or sucrose or both sugar are fermented, a large amount of acid will produce which turns both butt and slant yellow. So the appearance of yellow color in both slant and butt indicates that the isolate has the ability to ferment lactose or sucrose or both.