ANDRADE PEPTONE WATER

Different species of bacteria possess great variations in the ability to utilize carbohydrates and allied substances. Hence, the carbohydrate fermentation test is useful to distinguish between varieties of bacteria and identify them. The most common medium for the fermentation of carbohydrates is Andrade Peptone Water. The preferred carbohydrates are added separately to the medium, and it is inoculated with the test organism.
In the carbohydrate fermentation method, the organisms that can metabolize the provided carbohydrates will lower the pH of the medium by producing acids. This reaction makes the colour of the indicator change from colourless to pink to red. No colour change in the medium, which will remain in pale tan to straw colour, will show organisms that could not metabolize the added carbohydrate. The gas, which is collected in Durham’s tube indicates organisms fermenting carbohydrate with the production of gas.
The Andrade indicator is a solution of acid fuchsin which when titrated with sodium hydroxide changes colour from pink to yellow. The peptone used in the medium is free from fermentable carbohydrates and the medium is also free from nitrates which may interfere with gas production.

A basal medium to study fermentation reactions by adding carbohydrates.