Decarboxylase medium
From Bugwoodwiki
Purpose
Ingredients
| Ingredient | 1 L | 500 ml |
|---|---|---|
| Distilled water | 1000 ml | 500 ml |
| Peptone | 5 g | 2.5 g |
| Beef extract | 5 g | 2.5 g |
| Brom Cresol purple (0.2% aq.) | 5 ml | 2.5 ml |
| Cresol red (0.2% aq.) | 2.5 ml | 1.25 ml |
| Glucose | 0.5 g | 0.25 g |
| Pyridoxal | 0.005 g | 0.0025 g |
Instructions
- Divide the basal medium into four equal portions. One portion remains free of amino acids, to serve as a control, while the others receive lysine, ornithine, and arginine, to make 1% (10 g/L) solutions of each, respectively. If only DL forms of the amino acids are available, then add enough to make 2% solutions (20 g/L).
- The pH of the medium should be adjusted to 6.0-6.5 prior to autoclaving by adding 40% NaOH solution, one drop at a time, until the pH and color are correct. The medium should be violet in color. Caution: NaOH is very caustic. Dispense 4 ml of the medium into test tubes, cap, autoclave, and label.
- Inoculate tubes and cover with a layer of sterile mineral oil. Incubate and examine for up to 4 days.
Expected Results
- A positive reaction occurs with the release of amines and subsequent alkalinization. The tubes will change first to yellow then back to violet or reddish violet for a positive test, but will stay yellow if the test is negative. If the mineral oil is omitted, the tubes will show a false positive reaction.
Notes
References
- Difco Manual, 10th Edition. 1984. Difco Laboratories, Detroit, MI. 1155 pp.
Contributed by
From the Culture Media for Plant Pathogenic Fungi and Bacteria, University of Massachusetts: Contributed by Robert L. Wick
