The urease test is a biochemical assay that detects the presence of urease, an enzyme that hydrolyses urea to ammonia and carbon dioxide. Many bacteria produce urease to neutralize their environment; this test helps distinguish urease-positive organisms from those that lack the enzyme.nt; this test helps distinguish urease‑positive organisms from those that lack the enzyme.
Principle and method
Urease catalyses the hydrolysis of urea into ammonia and carbon dioxide. The test medium contains urea and a pH indicator such as phenol red. In the classical broth method, bacteria are inoculated into urea broth; urease activity releases ammonia, raising the pH and changing the indicator from yellow to bright pink. In urea agar slants, the same reaction produces a fuchsia color in the slant. Rapid urease producers like Proteus species turn the medium pink within a few hours, whereas weak producers like Klebsiella yield slower reactions. Organisms lacking urease, such as Escherichia coli, do not alter the medium. Incubation is typically at 35–37 °C and results are read at intervals up to 24 hours.
Diagnostic applications and interpretation
The urease test is an important tool in clinical microbiology. It is used to distinguish Proteus, Morganella and Yersinia species from other enteric Gram‑negative rods and to identify Brucella and Cryptococcus species. In gastroenterology, rapid urease tests (CLO test) detect Helicobacter pylori in gastric biopsies by exploiting the bacterium’s strong urease activity. Positive results are indicated by a color change to pink or red; negative tests remain yellow or orange. False negatives can occur with heavily inoculated media that overwhelm the pH change or with organisms growing poorly. Interpretation should consider incubation time and the strength of urease expression. The urease test provides a simple means to detect urease activity and aids in the identification of pathogenic bacteria and fungi. Its rapidity and ease of interpretation make it a standard component of biochemical identification panels. Related Terms: Urease, Proteus, Biochemical Test, Phenol Red, Helicobacter pylori