Capsule Stain of Mystery Bacteria

CAPSULE STAIN OF MYSTERY BACTERIA

Class: Tuesday, September 24th, 2013

In today's lab, we prepared our mystery bacteria with a capsule stain. The capsule stain is a type of negative staining. Similar to the negative stain we did in another lab, the purpose of this type of stain is to view bacterial capsules, which are difficult if possible with basic dyes. A bacterial capsule is one type of glycocalyx, the other type is a slime layer. However, slime layers are highly unorganized and easily detach from the cell wall, so the chances of even seeing a slime layer is slim if at all. Therefore, our main focus in this lab is to determine whether our bacteria has a capsule surrounding the cell wall.  If our bacteria has a capsule, a halo surrounding it will remain unstained. This "halo" is the bacterial capsule. 

A little background on bacterial capsules, they consist of polysaccharides usually combined with lipids and proteins, which adds to the organized structure of the capsule. The capsule acts as armor on the bacteria, protecting it from being eaten by phagocytic white blood cells. So bacteria with capsules stand a better chance of surviving in the human body than other bacteria that may not have a capsule.

To start the procedure, we prepared a negative stain of our mystery bacteria. We used the same technique as we did in our previous negative staining lab with nigrosin.

Negative stain of mystery bacteria using nigrosin

Magnified view of negative stain bacteria

After we placed our bacteria in a negative stain and let it air dry, we covered it with crystal violet. After the appropriate time of letting the smear soak in crystal violet, we gently rinsed off the excess stain. We were very careful with this step because the smear could very easily be removed. The goal is to NOT remove much of the smear.

      

We blotted the slide dry with pieces of bibulous paper, and then looked at our slide under a microscope to see some pretty cool stuff. However, sadly we saw no capsule surrounding our mystery bacteria...But we took a pretty awesome picture of it!

                                    

Random Dr. P's Experiment: We were given a bacteriophage to be tested with our mystery bacteria J. We inoculated bacteria J and streaked it onto the agar plate in a zig-zag fasion. The bacteriophage was streaked over top in the shape of our initials-JSM. This is to demonstrate how bacteriophage will kill the bacteria it touches.