CHRISTENSEN AGAR BASE

For the differentiation of a variety of microorganisms on the basis of urease production.

Code: CB1/7277

Typical formula g/l

Peptone	1.0
Glucose	1.0
Sodium chloride	5.0
Monopotassium phosphate	2.0
Phenol red	0.012
Agar	15.0

Final pH 6.8 +/- 0.2

Directions

Suspend 24g in 950ml of cold distilled water, heat to boiling with frequent agitation and sterilise by autoclaving at 121°C for 15 minutes. Cool to approximately 45°C and add under aseptically 50ml of Urea 40% Solution. Mix well and dispense the complete medium in quantities of 10ml into sterile tubes or bottles. Allow to cool in a sloping position.

Description

Christensen Agar base is prepared according to the formulation recommended by ISO/DIS 6579. Christensen Agar Base is used to detect the production of urease by Proteus, Klebsiella and certain yeasts such as Cryptococcus and as an identification test for the differentiation of Salmonella spp. (urease negative).

Method

Streak the agar slope surface with a pure culture to be tested. Do not inoculate the butt, to have the control colour of the negative reaction. Incubate at 37°C for 18-24 hours and examine at intervals. If the reaction is positive, splitting of urea liberates ammonia, which changes the colour of phenol red to rose-pink and later to deep cerise. The reaction is often apparent after 2-4 hours.

References

Christensen, W.B. (1946). J. Bact., 52,461466