Biochemical tests


Written by MicroDok

Voges-Proskauer (VP) test test is used to identify Gram negative bacteria that produce 2,3-butanediol (acetoin) from the fermentation of glucose. Some bacteria utilize glucose producing acetyl methyl carbinol which is oxidized in the presence of alkali to diacetyl. The presence of diacetyl is confirmed by the formation of red colour with arginine, creatine or creatinine. VP positive bacteria turn the medium in which they are inoculated to brownish-red to pink because they produce acetoin. Bacteria that are VP negative turn the inoculated medium to brownish-green to yellow. Klebsiella pneumoniae and Enterobacter aerogenes are VP positive bacteria.


  1. Prepare and sterilize glucose-phosphate as the growth medium and cool to room temperature.
  2. Inoculate the glucose-phosphate medium with the test bacterium.
  3. Incubate medium at 37oC overnight.
  4. Add 5 mg of creatine followed by 5 ml of 40 % NaOH and shake the tube very well.
  5. Observe tube(s) for a change in colour. Change of the colour of the medium to brownish-red to pink signifies a positive VP test.

Illustration of Voges Proskauer test

Tube on left side is negative while tube on right side is positive as indicated by the red colour.


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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