Gram-negative

 Gram-negative refers to a classification of bacteria based upon their cell wall structure. Gram-negative bacteria appear red as a result of Gram testing, whereas Gram-positive stain purple.

The structure of the Gram-negative bacterial cell wall is what distinguishes it from Gram-positive bacteria. Gram-negative bacteria contain a much thinner layer of Peptidoglycan in comparison to a Gram-positive bacterial cell wall. The Gram-negative cell wall consists of a unique outer membrane, containing lipopolysaccharides, murein lipoproteins and porin channels. There is also a periplasmic space between the peptidoglycan cell wall, and the cell membrane.

Gram-negative bacteria exhibit stronger resistance to Antibiotics such as Lysozyme and pennicillin G, as well as greater resistance to dyes and detergents.  The lipopolysaccharide consists of a core polysaccharide, Lipid A and O-antigen. This lipolysaccharide layer is important in excluding large hydrophobic susbstances from interacting with the cell. Lipid A attaches to the outer membrane ensuring that the lipopolysaccharide remains attached to the cell.