Urease test

Principle

Urease splits urea to ammonia, raising the pH; the phenol red indicator in Christensen's urea agar turns pink.

Procedure

• Inoculate the slant surface heavily; incubate at 35 °C and read at 4–6 h and 24 h (up to 7 days for some organisms).

Results

• Rapid positive (pink within hours): Proteus, Morganella, Providencia rettgeri
• Slower positive: Klebsiella, Enterobacter, Cryptococcus (yeasts)
• Negative: yellow (e.g. E. coli)

Related

Helicobacter pylori has very strong urease, the basis of the rapid urease (CLO) test and urea breath test.