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The Non-Enteric Rods: Urease test

Some bacteria contain the enzyme urease, which catalyzes the hydrolysis of urea, yielding alkaline ammonia produts which turn the pH indicator in the urease agar red. The results of the urease test shown here are as follows, from left to right:

Negative
Positive, entire tube is bright pink (typical for Bordetella
Positive, pink just on the slant
Uninoculated.

NOTE: E.coli and Salmonella are negative. Klebsiella is often positive after 24 hours but only Proteus is positive within four hours.