This video outlines
Fermentation of simple sugars testing this with the Durham, or what's often called the carbohydrate - this is a broth
medium so in the tube you'll notice that you have
an additional inverted tube inside which is a glass tube and that is there to catch air bubbles.
So we can test for the ability of an organism to ferment a particular simple sugar and we can have different sugars in different tubes
If the organism can ferment that particular sugar we say it has the enzymes with which to do so
We also can look to see if the organism produces gas in the course of
fermentation and that's what that inverted glass tube is for inside.
Now the indicator here is phenol red. 
 Phenol red starts out red
which you actually see here on the left that looks almost like a uninoculated tube even though it's not.  And
phenol red will turn yellow if the pH drops when an acid is produced.
So here on my lactose tubes on the left. I've got the yellow
which indicates acid is produced, the phenol red turned yellow
Any other color, orange, red
that we call that a negative that the organism does not have the particular enzyme in this case lactase to ferment lactose.
On the left here
We can see that this remained red so the phenol red did not react with an acid because there was not
Fermentation of lactose that produced an acid end product.  Another thing to note here is that
inverted tube.  So if that is cleared out at least a third of the way
Not just a little bit at the tip because sometimes that can happen during the manufacturing of the tube
But if there are enough air bubbles to clear out about a third of the tube
We say that the organism can also produce CO2 in the course of
fermentation.  You would only see this with an acid production because that's going to be in line with the acid production and the fermentation.
On the right here, you've got the sucrose tubes the same idea again
If an acid is produced you get a yellow color.  Now on this one you don't get the air bubbles produced at the top
Put that little bit closer to see
Yeah, you can see that
There's no air bubbles produced there
As opposed to one that does have the air bubbles you can see the clearing pretty well there I think.
So the yellow product acid production phenol red, which is our indicator turns yellow
So that in this case, since sucrose is a simple sugar
that's used
we can say that the organism is positive for the fermentation of sucrose or we can say has the
sucrase enzyme and
Right next to it here in the red
The red results that is a negative because again
We didn't get that acid production.  And we can put a variety of
simple sugars in different tubes. One nice thing to do with these is to use them in conjunction with a TSI tube in particular.
A TSI slant, because TSI has multiple sugars in there.  So this can help narrow down or give us additional
Supporting information as to which sugars are fermented and that is the carbohydrate
fermentation with Durham tube
