Description
Amyl Lysine Iron Agar, AM 80, is based on the formulation developed by Edwards and Fife1 for the detection of Salmonella species and, more particularly, rapid lactose fermenting strains of Salmonella arizonae.
The medium will detect those members of the Family Enterobacteriaceae that have the ability to decarboxylate lysine, forming the alkaline amine cadaverine, and produce hydrogen sulphide. Deamination of lysine by some members of the Proteus-Providencia group of organisms, will produce α Keto carboxylic acid. Production of acid from fermentation of glucose by organisms that are negative for lysine decarboxylase may suppress the formation of H2S.2
Peptones and yeast extract provide the necessary growth requirements for non-fastidious organisms, while glucose is a source of carbohydrate, fermentation of which creates the acidic conditions ( pH 6 ) required for the decarboxylation reaction. This medium cannot be used to determine the production of lysine decarboxylase by organisms that are unable to ferment glucose.
The production of hydrogen sulphide( under pH neutral or alkaline conditions), is detected by the formation of black ferrous sulphide, and bromocresol purple pH indicator changes the colour of the medium to violet under alkaline conditions ( pH > 6.8 ), and to yellow under acid ( pH < 5.2) conditions
