Question

A positive PDase test will result in what color change in the media when the appropriate reagent is added?

Answer 1

ANSWER 1 :-

The PDase test indicates Phenylalanine deaminase test. This test checks the ability of the microorganisms to produce the enzyme deaminase which is used to remove the amine group from Phenylalanine. The media containing Phenylalanine (amino acid) is converted to Phenylpyruvic acid. A reagent called as Ferric Chloride is added which reacts with Phenylpyruvic acid to produce a dark green coloured appearance in the media. The Ferric ions chelates the structure. Presence of this coloured media indicates a positive test and thus helps in differentiation between specific microbes.

ANSWER 2 :-

Phenol-red media is composed of a sugar such as glucose, phenol red dye. When the microorganisms are added to the media and they are able to fermentation the sugar into the media, the sugar gets converted to an acid which in turn makes the pH of the media acidic or less than 7. This can be indicated as a colour change forming a yellow coloured complex of the phenol red dye. This indicates positive test indicating fermentation has occured.

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