Methyl Red-Voges Proskauer

(MRVP) Test




 
 

Purpose:  The Methyl Red (MR) test is used to identify mixed acid fermenting bacteria that yield a stable acid end product.  The Voges-Proskauer (VP) test is used to identify bacteria capable of 2,3 butanediol fermentation following mixed-acid fermentation.

Principle: MRVP media contains glucose, peptone and phosphate buffer.  Many enteric organisms can overcome the buffering capacity of the media by producing large quantities of a stable acid end product, thus lowering the pH.  Acid produciton is detected using the pH indicator methyl red (red pH<4.4, yellow pH > 6).  In order to insure that the acid is stable this test should be conducted a minimum of 48 hrs. post inoculation.

Some organisms do not produce stable acid end products and instead further metabolize acids to more neutral end products like 2,3 butanediol.  The reagents used however, don't test for 2,3 butanediol, but rather it's precursor acetoin. 


 

Methyl Red Test Results:

These tubes show the results of a typical methyl red test.


Tube A.  Methyl red negative

Tube B.  Methyl red postive

Voges-Proskauer Test Results:

 

These tubes show the results of a typical Voges-Proskauer test.


Tube A.  Voges-Proskauer positive
 

Tube B.  Voges-Proskauer negative

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