Science Buddies: "Ask an Expert"

Hello,

Does anyone know how to preform a gram stain? Where can I get the materials?

Thanks

Hi John,

I have never performed a gram stain myself, though I understand how it works conceptually. Gram positive bacteria have thick cell walls, which soak up the purplish stain; gram negative bacteria have a thin cell wall underneath a membrane, and do not stain as readily.

Here are a few links with a descriptions and protocols for gram staining:
http://serc.carleton.edu/microbelife/re ... stain.html
http://www.uphs.upenn.edu/bugdrug/antib ... /Gram2.htm
http://www.life.umd.edu/classroom/bsci4 ... mStain.htm

There is even a YouTube video about it!
http://www.youtube.com/watch?v=OQ6C-gj_UHM

I found these links and more with a simple Google search for "gram staining." You can try looking for more of them yourself.

Let us know if you have more questions!

Heather

Hi John,

The links that Heather gave you have really great explanations and protocols. I wanted to add a couple tips that I use for my own gram staining.

-The ethanol/acetone decolorizer will remove any marker that you put on your slide. When I mark on the glass slide where my sample is I use a china marker (grease pencil) to do the writing. These resist the decolorizer better.

-When doing the water rinses you don't want to wash right over where your sample is. The water pressure can wash off some of your sample. I usually place the back side or edge of the glass slide under the stream of water. That way the water is moving much slower as it reaches you sample.

-Make sure to use fresh bacteria. As a bacterial culture gets old the cell walls get thicker. This can cause a false positive (gram negative bacteria may appear gram positive).

I hope that helps.
Kierstyn

Thank you very much