Unlike Gram-positive bacteria, which asuume a violet color in Gram staining, Gram negative bacteria incorporate the counterstain rather than the primary stain. Because the cell wall of Gram(-) bacteria is high in lipid content and low in peptidiglycan content, the primary crystal-violet escapes from the cell when the decolorizer is added. This is because primary stains like to bind with peptidoglycan- something the G(-) cell lacks. The pathogenic nature of Gram(-) bacteria is usually associated with certain components of their cell walls, particularly the lipopolysaccharide (endotoxin) layer.The Black Plague, which wiped out a a third of the population of Europe, was caused by the tiny G(-) rod, Yersinia pestis. Most enteric (bowel related) illnesses can also be attributed to this group of bacteria.
