The urease test
Principle: to determine the ability of an organism to split urea, forming two molecules of ammonia by the action of the enzyme urease.

This urease test, based on the process involving the hydrolysis of urea, was performed to help identify the Gram-negative enteric bacterium Yersinia enterocolitica. The hydrolysis of urea is confirmed by the formation of ammonia, and CO2, which alkalinizes the medium, and results in a pH shift. A "hot-pink" coloration, as seen in the tube at right, indicates a positive reaction, i.e., urea hydrolysis, and a yellow color, as in the tube on the left, indicates a negative reaction. Yersinia enterocolitica bacteria contain the urease gene cluster that enables them to hydrolyze urea (in most strains), however, though this test may yield positive results, Y. enterocolitica is not the only organism that can perform this process (other common urease positive bacteria are for example Klebsiella pneumoniae, Proteus spp., Morganella morganii, Providecia rettgeri), and further testing would be required in order to rule out the presence of other urease producing bacteria.