Moeller Decarboxylase Broth Base

 Principle

• Moeller Decarboxylase Broth Base is used for the differentiation of enteric bacilli on the basis of their ability to decarboxylate amino acids.
• The media is composed of peptone, special peptone, dextrose, bromocresol purple, cresol purple and pyridoxal. Peptone and special peptone provides nitrogen, vitamins, minerals, amino acids and growth factors. Dextrose is a carbon or energy source for the growth of microorganisms. Pyridoxal is the co-factor of the decarboxylase enzyme.
• 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 while putrescine is produced due to ornithine decarboxylation. Arginine is first hydrolyzed to ornithine which is then decarboxylated to form putrescine.
• Formation of these amines increases the pH of the medium, changing the colour of the indicator from yellow to purple.
• If the organisms do not produce the appropriate enzyme, the medium remains acidic and yellow in colour.
• The decarboxylase activity is compared with the Moeller Decarboxylase broth base lacking the amino acid. Inoculated tubes must be protected from the air with a layer of sterile mineral oil. Exposure to air may cause alkalinization at the surface of the medium which makes the test invalid.

Use: Recommended to differentiate bacteria on the basis of their ability to decarboxylate the amino acids.