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Principle
- Lysine Decarboxylase Broth is a modification of Moeller decarboxylase broth (1954-55). The media is composed of peptone, yeast extract, dextrose, L-lysine hydrochloride, and bromocresol purple.
- Peptone and yeast extract provide nitrogen, vitamins, minerals, amino acids, and growth factors. Dextrose is a 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 color of the indicator from purple to yellow. The acid produced stimulates the decarboxylase enzyme.
- Decarboxylation of lysine yields cadaverine in alkaline conditions, revert to purple color. If the organisms do not produce decarboxylase enzyme, the color of the medium remains yellow.
- Dextrose non-utilizers will not show any change in the medium color. Use light inoculation and do not read the tests after 24 hours of incubation, as some organisms require longer incubation time of up to 4 days.
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