Nessler's reagent is used to detect production of ammonia.Bacteria decompose urea by means of the enzyme urease. The occurrence of this enzyme can be tested by growing the organism in the presence of urea and testing for alkali (NH3) production by means of a suitable pH indicator. An alternative method is to test for the production of ammonia from urea by means of Nessler's reagent and/or to detect NH3 production due to L-arginine breakdown.