How does peptidoglycan affect gram staining?

1 Answer
Jul 1, 2014

Gram staining is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents.

The Gram stain procedure distinguishes between Gram positive and Gram negative groups by coloring these cells red or violet.

Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.

Alternatively, Gram negative bacteria stain red, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decolorizing process.

All steps are done even if the lab tech thinks she knows what the results will be.

Gram staining involves three processes: staining with a water-soluble dye called crystal violet, decolorization, and counterstaining, usually with safanin (light red).

Due to differences in the thickness of a peptidoglycan layer in the cell membrane between Gram positive and Gram negative bacteria, Gram positive bacteria (with a thicker peptidoglycan layer) retain crystal violet stain during the decolorization process, while Gram negative bacteria lose the crystal violet stain and are instead stained by the safranin in the final staining process.