Introduction
The Urease Test is an important biochemical test in microbiology used to detect the ability of bacteria to produce the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide.
This test is widely used for differentiating Enterobacteriaceae, identifying Proteus species, and detecting Helicobacter pylori.
Principle
The enzyme urease hydrolyzes urea into:
Ammonia (NH₃)
Carbon dioxide (CO₂)
Ammonia increases the pH of the medium, making it alkaline.
The medium contains phenol red as a pH indicator:
Yellow → Neutral/Acidic
Pink/Red → Alkaline (positive result)
Procedure
Prepare Christensen’s urea agar slant (contains urea and phenol red indicator).
Inoculate the medium with the test organism.
Incubate at 37°C for 24–48 hours.
Observe for color change:
Pink → Positive
No color change (remains yellow/orange) → Negative
Interpretation
| Result | Observation | Interpretation |
|---|---|---|
| Positive | Pink or red color in the medium | Urease enzyme present, urea hydrolyzed |
| Negative | No color change (remains yellow/orange) | Urease enzyme absent |
Examples of Bacteria
Urease Positive Bacteria
Proteus spp. (strongly positive, rapid)
Klebsiella pneumoniae
Helicobacter pylori
Corynebacterium urealyticum
Cryptococcus neoformans (fungus)
❌ Urease Negative Bacteria
Escherichia coli
Salmonella spp.
Shigella spp.
Pseudomonas aeruginosa
Uses of Urease Test
Differentiation of Proteus spp. (urease positive) from other Enterobacteriaceae.
Identification of Helicobacter pylori in gastric infections.
Helps distinguish Klebsiella (positive) from E. coli (negative).
Useful in mycology (e.g., Cryptococcus detection).
Important in clinical microbiology laboratories for bacterial identification.
Conclusion
The Urease Test is a simple and rapid biochemical test that detects urease enzyme activity in bacteria. It plays a crucial role in differentiating Proteus, Klebsiella, and Helicobacter pylori, making it highly valuable in diagnostic microbiology.
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