Description
This culture medium complies with the recommendations of the International Organization for Standardization ISO (1993) and the DIN Norm 10160.
Mode of Action
Urea is hydrolysed to carbon dioxide and ammonia by the enzyme urease. The ammonia formed then causes the medium to become alkaline; this reaction is detected by the indicator phenol red which changes its colour from yellow to purple (see also JEFFRIES, 1964).
Typical Composition (g/litre)
Peptone from meat 1.0;
D(+)glucose 1.0;
sodium chloride 5.0;
potassium dihydrogen phosphate 2.0;
phenol red 0.012;
agar-agar 12.0.
Also to be added:
Urea 20.0 g/litre.
Preparation
Suspend 21 g/litre, autoclave (15 min at 121 °C). Prior to use, liquefy the medium, cool to 45-55 °C and add 50 ml of a filtersterilized 40 % urea solution. Prepare slant-agar tubes.
pH: 6.8 ± 0.2 at 25 °C.
The prepared medium is clear and red.
Experimental Procedure and Evaluation
Inoculate the medium massively by spreading the pure culture
under investigation on the surface of the agar.
Incubation: 5-48 hours at 35 °C.
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