Question

6.What do we test for in the Voges-Proskauer test?

a. Name a species that will test positive.

7.What are the fermentation products made by bacteria which carry out mixed acid fermentation?

Answer 1

Answer

6. The Voges-Proskauer (VP) test is employed to determine if an organism produces acetylmethyl carbinol from glucose fermentation.The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth that has been inoculated with which. If present, acetylmethyl carbinol is converted to diacetyl in the presence of ∝- naphthol, strong alkali (40% KOH), and atmospherical oxygen.

a, species that will test positive

Enterobacter,Viridans group streptococci (except Streptococcus vestibularis), Listeria, Klebsiella, Serratia marcescens, Hafnia alvei, Vibrio eltor, Vibrio alginolyticus, etc.

7. bacteria which use the mixed acid pathway, which produces acidic end products such as lactic, acetic, and formic acid. These acidic end products are stable and will remain acidic.

Additional information About Voges-Proskauer (VP) test

Procedure
Inoculate a tube of MR/VP broth with a pure culture of the test organism.
Incubate for twenty-four hours at 35°C
At the end of this time, aliquot one ml of broth to clean tube.
Add 0.6mL of 50 α-naphthol, followed by 0.2 ml of 400th KOH. (Note: it's essential that the reagents be added during this order.)
Shake the tube gently to expose the medium to atmospheric oxygen and permit the tube to stay undisturbed for ten to fifteen minutes.

Results and Interpretation

A positive test is described by the development of a red color 15 minutes or more after the addition of the reagents indicating the presence of diacetyl, the oxidisation product of acetoin. The test shouldn't be read when standing for over one hour as a result of negative Voges-Proskauer cultures may turn out a copper like color, potentially leading to a false positive interpretation.