Lysine Iron Agar

Lysine Iron Agar is used for differentiating microorganisms based on L-Lysine decarboxylation/deamination and the production of hydrogen sulfide. Edwards and Fife developed Lysine Iron Agar to detect?Salmonella?arizonae. Since this species ferments Lactose rapidly, it was found that hydrogen sulfide production on Triple Sugar Iron Agar was suppressed. By eliminating Lactose and using L-Lysine, this medium differentiates enteric bacilli based on their ability to decarboxylate or deaminate this amino acid. Sodium Thiosulfate and Ferric Ammonium Citrate reveal the production of hydrogen disulfide by forming a black precipitate. Bromocresol Purple serves as pH indicator. Organisms that decarboxylate L-Lysine, such as?Salmonella?spp., produce the alkaline compound cadaverine and the slant remains purple, while those deaminating it, such as?Proteus?spp., convert this amino acid to ?-ketocarboxylic acid and produce a color shift to red.