Urea Agar was described by Christensen which detected urease activity by all rapidly urease-positive Proteus organisms and also by other members of Enterobacteriaceae that exhibited a delayed urease reaction. This is accomplished by
a) adding glucose to the medium
b) decreasing the peptone concentration, and
c) decreasing the buffering system, as a less buffered medium detects even smaller amount of alkali.
ISO Committee has recommended Urea Agar Base, Christensen (M112I), with one phosphate, instead of two phosphates for detection of rapid urease activity.
Heavy inoculum of growth is inoculated on the surface of the slants. On incubation urea is utilized to form ammonia, which makes the medium alkaline, showing a pink-red colour by the change in the phenol red indicator. Prolonged incubation may cause alkaline reaction in the medium. Check using medium without urea as the negative control.
Peptic digest of animal tissues is the source of essential nutrients. Dextrose is the energy source. Sodium chloride maintains the osmotic equilibrium of the medium whereas phosphates serve to buffer the medium. Urea is hydrolyzed to liberate ammonia. Phenol red indicator detects the alkalinity generated by visible color change from orange to pink.
Storage and Shelf-life:
Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.