"Most bacteria can be broadly classified as Gram positive or Gram negative.
Gram positive bacteria have cell walls composed of thick layers of peptidoglycan.
Gram positive cells stain purple when subjected to a Gram stain procedure.
Gram negative bacteria have cell walls with a thin layer of peptidoglycan. The cell wall also includes an outer membrane with lipopolysaccharide (LPS) molecules attached."
These bacteria, when performing the Gram staining technique, have a violet or dark blue stain. Gram-positive organisms are able to retain the violet dye due to the large amount of peptidoglycan in their cell wall. Cell walls of gram-positive organisms usually lack the peripheral membrane present in gram-negative bacteria.
Peptidoglycan, also called murein, is a peptide-bound heteropolysaccharide present in the prokaryote cell wall. It is formed by two types of sugars (N-acetylmuramic acid and N-acetylglucosamine) and some amino acids.
