Description

Urease hydrolyzes urea into ammonia, carbon dioxide and water.


Urea is NH2-CO-NH2 (diamide of carbonic acid.

 

The release of ammonia increases the pH of the media. Phenolphthalein is colorless at a pH 8.1, but becomes pink-red if the pH is > 8.1.

 

Bacteria with urease vary in its activity:

(1) some species hydrolyze urea rapidly, with 2 hours

(2) other species hydrolyze urea slowly, over several days

 

The most commonly used test media are:

(1) Stuart's urea broth

(2) Christensen's urea agar

Both contain a large amount of urea.

 

The inoculated media is incubated at 35°C.

 

Causes of a false positive:

(1) mixed isolate

 

Causes of a false negative:

(1) reading the tube at 24 hours (will fail to detect species with weak urease activity)


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