Urease Test

General Information About Urea Broth

Urea broth is a differential medium that tests the ability of an organism to produce an exoenzyme, called urease, that hydrolyzes urea to ammonia and carbon dioxide.  

Many enterics can hydrolyze urea; however, only a few can degrade urea rapidly. These are known as “rapid urease-positive” organisms. Members of the genus Proteus are included among these organisms.

Urea broth is formulated to test for rapid urease-positive organisms. The restrictive amount of nutrients coupled with the use of pH buffers prevent all but rapid urease-positive organisms from producing enough ammonia to turn the phenol red pink.

THE Basic Chemistry of Urea Broth

Urea broth contains two pH buffers, urea, a very small amount of nutrients for the bacteria, and the pH indicator phenol red.  Phenol red turns yellow below a pH of 6.8 and fuchsia above a pH of 7.4. If the urea in the broth is degraded and ammonia is produced, an alkaline environment is created, and the media turns pink.

Important: In our lab, we only use the urea broth, not the agar.

Reading the Results

Urease positive organisms will turn the medium pink. Urease negative organisms will not produce a color change in the medium.

Application of the Urease Test

Urease broth can be used to differentiate members of the genera Proteus, Morganella, and Providencia from other enterics.