Question

What are four possible reactions that can occur when different carbohydrates react with the TSI agar?

Answer 1

Ans) TSI medium contains three sugars that is glucose, lactose, sucrose and iron.

The indicator is phenol red

The four reactions or results from action of different carbohydrates are -

In case of lactose or sucrose fermentation the indicator shows a yellow colour in the slant and butt due to production of acid.

Acidic slant and acidic butt.

In case of glucose fermentation only the butt will turn yellow in color while the slant will remain red because butt contains higher concentration of glucose than the slant

That is alkaline slant and acidic butt.

3 - If none of the sugars in the medium is fermented that is lactose, sucrose or glucose are fermented the slant and the butt reaimins red in color.

So either alkaline slant and no change in butt or alkaline slant and alkaline butt.

4 - If hydrogen sulfide is produced the slant turns black as the sulphur combines with the iron to form ferrous sulphide.

If this helps, give it a positive rating. Thank you.