AAT Bioquest

Is peptidoglycan presence signify Gram-positivity or Gram-negativity?

Posted August 6, 2021


The cell walls of both Gram-positive and Gram-negative bacteria contain peptidoglycans so the presence of peptidoglycan by itself does not signify Gram-positivity or Gram-negativity. The difference lies in the composition of peptidoglycans in the cell wall of each.

Gram-negative bacteria have a relatively thin cell wall made up of a few layers of peptidoglycan about 7 to 8 nanometers in thickness. Peptidoglycan makes up about 10% of the cell wall dry weight in Gram-negative bacteria.

Gram-positive bacteria have a thicker cell wall made up of multiple layers of peptidoglycan about 20 to 80 nanometers. Peptidoglycan makes up about 20% of the cell wall dry weight in Gram-positive bacteria.

Additional resources

Mechanism of gram variability in select bacteria

MycoLight™ Rapid Fluorescence Gram-Positive Bacteria Staining Kit

Gram Staining