This video provides an overview of the Methyl red / Vogues Proskauer test
This test is starts with a basic T soy broth with glucose present and
We're looking to see what type of end products are produced whether they are an acid end product due to mixed acid production
Or whether it's a neutral - maybe even slightly basic end products. We're basically looking for a pH change through various reagents
This is a medium that is split into two tubes
So you put the same bacterium into both tubes the same species of bacterium,
Incubate and then you add the reagents so here on the left we have Methyl red reagent. That's been added
and
the
Test result of [its] staying a bright
red indicates that it is a
positive for the
Production of mixed acid so the pH is dropped and we did the exact same incubation here with the same organism
We just simply added a different reagent at the end of the incubation period
Consuming here, just a little bit and here. We added the [VP] reagent the VP reagent is a
Combination Vogues Proskauer reagent is a combination of two reagents, and it's somewhere around eight drops of A to four drops of B
but that can vary so always check with your instructor on that and that needs an
Incubation time of somewhere from five to ten minutes
Maybe even up to [fifteen] and that varies a little bit depending on again. Just the type of
Particular type of VP-A and VP-B reagent [that] we use now. You should never see a positive for both tests
So what I see here on the left is a positive for Methyl red and that tells me this organism makes acid end products
And I got a negative for the VP
Test which also confirms that the end products are not neutral to basic because I didn't get a positive here
I got a red color of Methyl Red which indicates the end product is acidic
Now taking a different
Bacterium over here on the right. I now have the same set up. I have a Methyl red test
Against a VP test. I took again a different species of bacteria
But with the same species in each Tube. It's again a broth thats split in half with glucose and
I added Methyl red and in one tube to test for acid products in that particular tube
and then I added the VP-A and VP-B reagent to test for the pH change again neutral to maybe even
slightly alkaline
the
product that I'm looking for here actually what I'm looking for in particular is 2-3 butanediol
However the particular product that this test picks up is a precursor to that acetoin.  So I'm testing for acetoin
But if acetoin is present it's going to indicate that instead of mixed acids produced at the end of this fermentation
you're going to see a 2-3 butanediol that's produced or it could be also acetyl methyl carbonol
Again, it's key that the VP reagents are added in the correct amounts in the right order
And I compared a couple different Methyl red negatives here just to note on these methyl reds that
It clearly needs to be a bright red color so I'm going to move this other one over here pull this out
This is actually a negative methyl red. It's more of an orange color
It needs to be bright red to be considered positive over here here. You can see it. Clearly this is from the test
I started with a clear bright red color which is going to indicate an acidic end product anything other than that
So little to no red or here's almost kind of an orangey red is going to be considered a negative
And I should again see negative
This is a different species of bacteria. Which is slightly different change but again should see a negative
MR Test going along with with a positive VP test
And the VP test appears positive by the formation of a red ring at the top of the Tube [after] 15 minutes
So this gives again an overview of the MR-VP test which covers
the type of end products that are produced at the end of glucose fermentation you're either looking for acidic end products or
neutral end products
and I said neutral and can be slightly basic and
You're doing that by adding Methyl red to one tube to pick up any acidic products that might be there and then the other tube
with the same bacterium
Adding the VP reagents to pick up a a rise in pH, and that is the overview of the MR VP test.
