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Urease test

Urease test

The figure shows the result of an urease test, where tube A is a negative control. Tube B contains, Proteus sp. and tube C contains Escherichia coli. Note that a  pH change has occured in tube B because Proteus spp. are urease positive.

Image:Karl-Erik Johansson (BVF, SLU) and Lise-Lotte Fernström (BVF, SLU).

 

General

Some bacteria have the enzyme urease, which in the presence of H2O converts urea (=carbamide) to NH3 (ammonia) and CO2 (carbondioxide), which forms ammonium carbonate in the presence of water. See chemical reaction formula.
The urease test

Method

By growing the bacteria in urease medium containing a pH indicator, it can be determined if the bacteria express urease. If the bacteria have an urease, urea will be converted to ammonium carbonate and the medium will turn alcaline. Thus, the colour will change to red (cerise).

Urease medium:

Substance Amount (g)
Pepton 1.0
Glucose 1.0
NaCl 5.0
Disodium hydrogen phosphate 1.2
Potassium dihydrogen phosphate 0.8
Phenol red 0.004

Applications

The urease test can be used to distinguish between E. coli, which is urease negative, from Proteus spp., which are urease positive.

Updated: 2017-03-31.

 

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