UREASE TEST

Urease test is used to detect and differentiate Enterobacteriaceae that produce urease enzymes from those that do not. Urease positive enterobacteria produce urease enzyme which has the ability to breakdown urea to ammonia (NH3) and carbon (IV) oxide (CO2). To test for urease production in bacteria, test isolates are cultured in a medium that contains urea and an indicator phenol red which changes colour from yellow to pink following the release of NH3 which turns the medium alkaline. Urease test can be performed in the laboratory using modified Christensen’s urea broth, a urease testing tablet or a urea agar medium. Proteus, Klebsiella and Providencia species are strong producers of urease enzymes.

Procedure

  1. Prepare urea agar medium slant in a test tube according to manufacturer’s instruction. In the preparation, test tube(s) containing the citrate medium must be kept in slanting position in order to make a slope. Well prepared urea slant looks yellowish.
  2. Perform this test with a pure culture of the test isolate grown on a nutrient agar plate.
  3. Aseptically inoculate a speck or inoculum of the test isolate on urea agar medium slant by streaking.
  4. Incubate the slant(s) overnight at 37oC
  5. Observe the slant for a pink colouration. This is indicative of a positive result. Absence of a pink colour shows a negative test result, and nonexistence of a urease producer.

Illustration of urease test

Tube on left side is positive as indicated by the pink colour, tube at the center is an uninoculated tube and tube on the right side is negative.

REFERENCES

Cheesbrough M (2006). District Laboratory Practice in Tropical Countries. 2nd Cambridge University Press, UK. Pp. 178-187.

Willey J.M, Sherwood L.M and Woolverton C.J (2008). Harley and Klein’s Microbiology. 7th ed. McGraw-Hill Higher Education, USA.

Woods GL and Washington JA (1995). The Clinician and the Microbiology Laboratory. Mandell GL, Bennett JE, Dolin R (eds): Principles and Practice of Infectious Diseases. 4th ed. Churchill Livingstone, New York.

World Health Organization (1993). Laboratory Biosafety Manual, 2nd edn. Geneva: WHO.

World Health Organization (2003). Guidelines for the Safe Transport of Infectious Substances and Diagnostic Specimens.  WHO/EMC/97.3. Geneva: WHO.

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