Why do gram positive and gram negative bacteria produce colors with gram staining?

Question

explain the chemistry of the staining process

Answer 1

Okay, so gram pos. is made of peptoglycan so it stains a different color than the negative. Obviously gram positive has a thicker cell wall than the negative one. I'm not so certain about the chemical composition but it does have alcohol in it (which produces a different stain for those two types of bacteria).

According to infoplease.com "Gram-positive bacteria are generally more sensitive to growth inhibition by dyes, halogens, many antibiotics, and to attack by phagocytosis and are more resistant to digestion by the enzymes pepsin and trypsin and enzymes in animal sera."

Answer 2

The Peptydoglycan on the Gram Pos. Bacteria creates a thick, sticky wall that makes it harder to hold stain.  So when you dye it with the Crystal Violet, you then use the Gram's Iodine, which acts as a Mordant, fixing the dye to the thick cell wall.  You then use the Ethyl Alcohol sparingly to de-colorize, but the mordant should make the dye stay just on the bacteria.  You have to rinse with water pretty quick.

Then, when you stain again with the pink dye, it will stick only to the gram negative bacteria.  These are easy to stain, and don't need a mordant, cause they have a membrane outside of their cell walls. So you end up with purple Gram positive and pink Gram negative.  Yay!!!!