Question

What does a TSI tube with a red slant and a yellow buttom inducate? A yellow slant and a yellow buttom indicate?

Answer 1

Answer-

A TSI or Triple Sugar Iron Test is a kind of microbiological test which is roughly named for its ability to test a microorganisms ability to ferment Sugars and to produce hydrogen sulphide.

The TSI slant is basically a test tube which contains Agar, a pH sensitive dye (phenyl red), 1% lactose, 1% sucrose, 0.1% glucose as well as sodium thiosulphate and ferrous sulphate or ferrous Ammonium Sulphate.

The bacteria that ferment any of the three products in the medium will produce by product.

A bacterium which is a non lactose fermenter and ferments glucose will initially cause a yellow slant or yellow bottom (acid/acid reaction) after 8 hours. But this will then convert to a red slant or yellow bottom after 24 hours (alkaline/acid reaction). On the other hand, if it ferments both lactose and glucose it will result in a Yellow/yellow tube and remain that way due to a large amount of acid produced in the reaction.