Urease
Overview
Some bacteria can use the urea as the sole source of nitrogen. In such a case the bacteria must have an enzyme, the urease, which can attack the urea. When it is broken down it releases ammonia that alkalizes the culture medium.
The culture medium has a pH indicator that turns a deep pink color when this pH becomes basic; in this way the production of ammonia and, ultimately, the presence of the urease enzyme, can be detected. The culture medium to be used is agar urea.
Carrying out the practical
A Petri dish that contains the agar urea medium is inoculated using the inoculation loop technique.
It is incubated at 37ºC for 24 hours at the end of which the medium is observed to see if it has turned a light amber color initially, which then goes deep pink (fuchsia).
The possible positive results are shown in the following figures. Some bacteria produce a large amount of the enzyme and the whole plate turns a fuchsia pink color, and others produce less and the color is not as intense.
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