Saturday, December 29, 2012

Urease test: Principle, Procedure, interpretation and urease positive organsims



Medium used: Any urea medium, agar or broth
Indicator used: Phenol red
Color change:  
Original: orange yellow color
Final color (in positive test): Bright pink 

Test principle
Many organisms especially those that infect the urinary tract, have a urease enzyme which is able to split urea in the presence of water to release ammonia and carbon dioxide. The ammonia combines with carbon dioxide and water to form ammonium carbonate which turns the medium alkaline, turning the indicator phenol red from its original orange yellow color to bright pink.

Urease test is useful test: 
This test can be used as part of the identification of several genera and species of Enterobacteriaceae including proteus, klebsiella, and  yersinia species. It is also useful to identify Cryptococcus species, Brucella, Helicobacter pylori.

Name of urease positive organisms
  1. Helicobacter pylori
    Most species of Helicobacter pylori have strong urease activity. Biopsy urease test and urea breath test are commonly employed test for the presumptive diagnosis of Helicobacter pylori infection.
  2. Proteus spp
  3. Yersinia spp
  4. Corynebacterium spp
  5. Brucella spp
  6. Cryptococcus spp
Note:Mneomonics to remember urease positive organisms: PUNCH
i.e.
P: P
roteus
U:Ureaplasma
N: Nocardia
C: Cryptococcus neoformans/Corynebacterium spp
H: Helicobacter Pylori

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