urease test: Principle, Procedure, result microbiology

Urease test is an important biochemical test for the identification of certain kinds of bacteria like helicobacter pylori, proteus, morganella, and enterocolitis.

What is the principle of the urease test?

Some bacteria produce enzymes called urease. When they react with urea, they split it and convert it into ammonia (NH3) and carbon dioxide (CO₂). Ammonia changes the PH of the medium to alkaline. As a result color of the media changed.

what are reagents for the urease test?

Following reagents are used urease test.

• 1. Christensen medium
• 2. Peptone
• 3. Sodium Chloride (NaCl)
• 4. Dipotassium Hydrogen Phosphate
• 5. Phenol Red (Indicator) (1 in 500 aqueous solutions)
• 6. agar
• 7. Glucose
• 8. Urea 20 % solution

How to prepare urease test broth agar?

Following steps performed.

• a. First sterilize the urea and glucose solution by Sietz filtration.
• b. Prepare basal medium, adjust the PH between 6 to 7.
• c. Sterilize the basal media in an autoclave at 121 C for 30 minutes. After sterilization cool to 50 C
• d. Add glucose, urea, and media.

what is the procedure of urease test

1. Inoculate the colony of the test organism from culture over the entire slope surface and stab the medium.
2. Incubate at 37C inoculated medium.
3. Read after four hours, and again after overnight incubation.

Note: If the color of the medium did not change after FOUR days of incubation, then the result will be considered negative.

Which bacteria are urease-positive?

You can remember the list of urease positive bacteria by mnemonic (PUNCH KISS)

• 1. Proteus
• 2. Ureaplasma
• 3. Helicobactor
• 4. Nocardia
• 5. Klebsiella