Histidine discs are used for amino acid decarboxylation test. To determine amino acid decarboxylation, the Serine disc (DD054) is added in the Decarboxyalse Broth Base, Moeller (M393)which is used as a negative control for studying decarboxylation or as a base for the addition of amino acids. The test organismisinoculated into the broth containing the Serine disc (DD054). The inoculated tubes are overlaid with sterile mineral oil andincubated at 35-37°C for up to 4 days. Positive Test: Colour of the medium changes from yellow to purple. Negative Test: Colour of the medium changes to yellow or there is no change