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Principle
- Lysine Lactose Broth is formulated by Falkow (1985) is also named Falkow Lysine Broth use for the detection of lysine decarboxylase by means of a color reaction in enteric bacilli.
- The media is composed of peptone, yeast extract, dextrose, L-lysine hydrochloride, lactose and bromocresol purple. Peptone and yeast extract provide nitrogen, vitamins, minerals, amino acids and growth factors. Dextrose and lactose are carbon or energy source for the growth of microorganisms.
- L-lysine hydrochloride decarboxylated from cadaverine. Bromo cresol purple and cresol red are the pH indicators. When dextrose is fermented by bacteria, the pH is lowered due to acid production, which changes the colour of the indicator from purple to yellow.
- The acid produced stimulates the decarboxylase enzyme. Decarboxylation of lysine yields cadaverine in alkaline conditions, reverting to purple colour. If the organisms do not produce decarboxylase enzyme, the colour of the medium remains yellow.
- The enteric bacilli produce acid initially due to lactose fermentation. While lactose non-fermenters produce acid from dextrose resulting in the formation of yellow colour. Subsequently L-Lysine is decarboxylated to form cadaverine resulting in an alkaline reaction and the broth reverts to purple colour.
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