Urease Test- Principle, Media, Procedure, Result, Uses


The urease test is a biochemical test that detects the presence of the enzyme urease in microorganisms. Urease is an enzyme that catalyzes the hydrolysis of urea into ammonia and carbon dioxide. The production of ammonia raises the pH of the medium, which can be detected by a color change of a pH indicator.

The urease test is useful for identifying and differentiating various bacteria, especially those that cause urinary tract infections, such as Proteus, Klebsiella, and some Citrobacter and Yersinia species. It can also be used to identify other bacteria that produce urease, such as Brucella, Helicobacter pylori, Cryptococcus, and some Corynebacterium species.

The urease test can be performed using different media, such as agar slants, broth tubes, or disks. The most commonly used medium is the urea agar base (Christensen agar), which contains urea and phenol red as a pH indicator. Phenol red turns from orange-yellow to bright pink when the pH rises above 8.4. The test can also be performed using a rapid urease test kit, which involves placing a gastric biopsy sample on a urea broth with a red phenol indicator and observing for a color change within minutes.

The urease test is simple, inexpensive, and reliable. However, it has some limitations, such as the variability in the speed of urease production among different organisms, the possibility of false-positive results due to peptone hydrolysis or autohydrolysis of urea, and the need for proper storage and buffering of the medium.

In this article, we will discuss the objectives, principle, procedure, result interpretation, control organisms, uses, and limitations of the urease test in detail.