Phenol red broth base is the media that is used to grow most organisms and a large amount of a potentially fermentable sugar.
For the purpose of microorganism differentiation, phenol red broth base is advised to ascertain the fermentation response of carbohydrates.
Gram negative bacilli can be recognised with it, particularly Enterobacteriaceae. It includes one carbohydrate, a Durham tube, peptone, and phenol red (a pH indicator) (glucose, lactose, or sucrose).
When a carbohydrate is utilised by an organism, an acid byproduct is produced, which causes the media to turn yellow. If the organism can use the peptone but not the carbohydrate, ammonia is produced as a byproduct, which raises the pH of the medium and colours it fuchsia.
A gas byproduct could be created once the organism is able to utilise the carbohydrate. If so, the Durham tube will become caught by an air bubble. Gas will not be created and no air bubble will emerge if the organism is unable to use the carbohydrates .
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