Hello everybody. We're going to talk
about sugar fermentation.
Sugar fermentation is an assay in 
microbiology
that we do in order to determine if a
specific bacterium
is able to use a specific sugar as a
source of energy.
As food. The sugar could be anything, it
could be glucose, it could be
lactose, it could be sorbitol. It could
be any kind of sugar that you can think
of.
In this case, these two tubes are
they both have glucose. We're
checking specifically,
for glucose.
The only difference between these tubes
is that this one is liquid
and this one, as you can see, is solid.
If you're asking, how do you know if the
bacteria
were able to use the sugar? 
Both tubes, not only they both have
glucose, they both have methyl red.
That's why it looks kind of red to
pinkish color.
If the bacteria were able to use the
sugar
that is inside both tubes there will be
sugar fermentation,
the environment will turn acidic and
methyl red
would turn yellow
Like here. I'm gonna go into
more detail about
like the results.
To summarize again, if when you add the
bacteria,
the media stays red to pinkish 
color,
that means that the bacteria were unable
 to use the sugar.
If after you add the bacteria, the
media
turns yellow, that means that there was
fermentation, the environment turned acidic
and that means that the
bacteria were able to use
the sugar. You can also
check both of them, if they turn yellow
you know that the bacteria
were able to use the sugar.
You can test for gas production, just
because the bacteria
were able to use the sugar
doesn't mean that it produces gas. You
could you also check for gas production.
And checking for the gas production is
going to be different whether you're
using liquid
or solid. Let's start with the liquid one.
Let's start with the liquid one, if
you're using the liquid what you're
going to do is you're going to use a
small tube. I don't know if you can see
there is a small tube inside
the big tube. The small tube is called
the Durham tube.
And I'm going to show it, this is
the Durham tube. And this is an
empty
this is what we did. We
have these and then we put the
the liquid so the only difference
between this one
and that one is that, that one has the
liquid, it has the liquid and this one
doesn't.
The Durham tube is open on one side
as you can see,
and it's closed on the other side.
What you're going to do is, you're going
to put the open side
inside, you can see the open side inside,
upside down, inside the big
tube. Now, if there is gas production,
it's going to be trapped in the Durham
tube, in the small tube.
It's like, it's going to, gases what they
want to go up.
The gas is going to go up and it's
going to be trapped
at the tip of the Durham tube. That's how
you check for gas production in the
liquid.
In the solid, if you're using the solid
one,
you're going to see that the media
it's going to be look crack
and it's going to be pushed up. You're
going to see both of them.
We inoculated both of them.
I'm not gonna go into much detail
how we do that because you know we
learned that in a different video.
but for the liquid one you can just take
a loop
The loop and you're
gonna follow aseptic techniques of
course, you're gonna like flame
the mouth, you're gonna take the bacteria
with the loop, you're gonna put it in,
you shake it, you flame it again, remember?
and you're gonna close it.
For the solid one
we're going to use the needle,
you're going to go with the needle one
and
again i'm not going to go into much
detail because I know you learned that
already, you're going to take the needle
and you're going to
go, you're going to surface sterilize the
needle, you're going to flame
the mouth here, you're gonna go all
the way to the bottom
you're gonna inoculate it with bacteria
like with a needle with bacteria
all the way to the bottom.
We did that, we inoculated both tubes.
and let's check the results.
Here we have,
we have here, we have two different
bacteria, bacterium A and bacterium B
As you can see both bacteria,
bacterium A
and bacterium B were able to use
the sugar.  It turned yellow so that
means that the bacteria,
both bacteria, were able to use the sugar.
The difference between bacteria A,
bacterium A,
and bacterium B is that bacterium A was
able to produce
gas production, as you can see there
are bubbles
in the Durham tube, actually there
are a couple bubbles, there are three
bubbles.
Whereas bacterium B
was unable to produce gas, like you can
see the Durham tube doesn't have any
bubbles.
Just to summarize, both bacteria
were able to use the sugar.
Now
the environment is acidic so that means
that there has been sugar fermentation
but only one was able, only one bacterium,
was able to use the produce
gas.
In this case we have the same, we have
bacterium A bacterium B.
It's just that we are testing on 
solid. Remember, after you
inoculate
the tubes with bacteria you will
incubate them overnight and this was
these are the results of the day after.
As you can see both bacteria were able
to use the sugar.
They both are yellow. Now the difference
is that, let me remove the caps so
you can see.
The gas production, as you can see
bacterium A produced a lot of gas but in
this case it's not a bubble,
it's just the gas wants to go up it
cannot and it's just pushing the entire
media
up. And so you can tell definitely
that bacterium A
produced gas, and then
bacterium B is not producing any gas.
There is no the media, is just
just like it was originally and there is
no like cracks on the sides or anything.
So definitely
bacterium A produced gas, B
didn't produce gas.
