Lysine Decarboxylase Broth is used to detect and differentiate Enterobacteria from other microorganisms, based on lysine decarboxylation. Gelatin peptone provides nitrogen, vitamins, minerals and amino acids essential for growth.Yeast extract is a source of vitamins, particularly of the B-group. Dextrose is the fermentable carbohydrate. Bromocresol purple is the pH indicator. Lysine is added to detect the production of the specific enzyme. When the medium is inoculated with a bacterium that is able to ferment dextrose, the acid produced lowers the pH of the medium and changes the color of the indicator from purple to yellow. The acidic condition also stimulates decarboxylase activity. The bacteria that decarboxylate the L-Lysine to cadaverine are identified by the presence of a purple-red color. The production of these amines elevates the pH of the medium. A yellow color after 24 hours indicates a negative result. By substituting L-Lysine with Arginine or Ornithine, the new resulting medium (Falkow Broth Base) can be used to study the decarboxylation of these amino acids.
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