It is abbreviated MR/VP. MR stands for methyl red, and VP stands for Voges-Proskauer. It is used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation and glucose. I found this on wikipedia.com.
You use methyl red as a ph indicator for for the MRVP test.
MRVP media contains glucose,peptone and phosphate buffer.Many enteric organism can overcome the buffering capacityb of media by producing large amount of stable acids as end product,thus lowering the pH.this acid production is detected bt methyl red indicator,which remains red in color at a pH of 4.4 or less.9red pH<4.4 or less,yellow pH >6).