Urea Broth can be used for the determination of the urea activity of Enterobacteriaceae, as well as microorganisms of the families of Brucella, Bacillus, Micrococcus, Mycobacteria and Proteus. It can be used for the identification of bacteria on the basis of urea utilization. It is especially recommended for the differentiation of members of the genus Proteus from those of Salmonella and Shigella. Urea is a source of nitrogen for those organisms producing urease. Yeast extract is a source of vitamins, particularly of the B-group essential for bacterial growth. Potassium phosphates provide buffering capacity. Phenol red is the pH indicator. When organisms utilize urea, ammonia is produced during incubation, making the reaction of these media alkaline. Positive urease tubes turn the phenol indicator a deep violet-red color (alkalinization). Therefore, urease production may be detected by a change in the phenol red indicator. Developed by Rustigian and Stuart, this highly buffered medium usually reacts only to the high outputs of ammonia by Proteus, Morganella and Providencia in the first 24 hours of incubation.
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