General Information
This medium complies with the recommendations of the harmonised method in the European Pharmacopeia 5.6 and the United States Pharmacopeia 29 (2006).

Mode of Action
Degradation of xylose, lactose and sucrose to acid causes phenol red to change its colour to yellow. Production of hydrogen sulfide is indicated by thiosulfate and iron(III) salt, which react to form a precipitate of black iron sulfide in the colonies. Bacteria which decarboxylate lysine to cadaverine can be recognized
by the appearance of a purple colouration around the colonies due to an increase in pH. These reactions can proceed simultaneously or successively, this may cause the pH indicator to exhibit various shades of colour
or it may change its colour from yellow to red on prolonged incubation. The culture medium is weakly inhibitory.

Typical Composition (g/litre)
Yeast extract 3.0;
sodium chloride 5.0;
D(+)xylose 3.50;
lactose 7.5;
sucrose 7.5;
L(+)lysine 5.0;
sodium deoxycholate 2.5;
sodium thiosulfate 6.8;
ammonium iron(III) citrate 0.8;
phenol red 0.08;
agar-agar 13.5.

Preparation
1. Weigh out 55.2 g of XLD Agar.
2. Add 50 ml of demin. water to a flask
3. Transfer 55,2 g of XLD Agar gently to flask with swirling.
4. Mix thoroughly, add remaining 950 ml demin. water, until completely suspended. Check for lumps. If present repeat mixing.
5. Heat to boiling to dissolve completely (variously shaking).
6. Immediately cool the medium to about 47-50 °C in a waterbath set at this temperature. Agitate flask to cool rapidly.
7. Pour plates.
8. Dry plates and check for sterility prior to use.

Note: preparation of large volumes, overheating and prolonged storage in water bath (47-50 °C) should be avoided.
Do not autoclave.
pH: 7.4 ± 0.2 at 25 °C.
The plates are clear and red.