Amino Acid Decarboxylase Control (Escherichia coli O157, Salmonella and Shigella, Vibrio cholerae)

Principle of Test:After bacteria grow in the control tube for amino acid decarboxylase test, they decompose glucose in the medium and produce acid, which reduces the medium pH and turns the tube from purple to yellow;in the test tube, bacteria first decompose glucose to generate acid, also changing the color from purple to yellow. The acidic environment induces bacteria to synthesize amino acid decarboxylase. The enzyme breaks down amino acids in the tube to produce alkaline substances, which neutralize the prior acidic environment and raise the medium pH, turning the color back to purple. If the bacteria do not produce amino acid decarboxylase, the test tube will remain yellow instead of turning purple. So when observing the final results, if the control tube and the test tube are both yellow, it is negative for the corresponding amino acid decarboxylase; if the control tube is yellow while the test tube is purple, it indicates that the bacterial amino acid decarboxylase is positive.