In order to understand the action of the gram stain in differentiating the bacterium, we need to have a look at the cell wall composition of the bacteria .In them, the cell wall has a little difference .
Cell Wall in Gram positive bacteria –
- Has relatively thick layer of peptidoglycan ,
- Techoic acid (polymer of glycerol or ribotol connecterd with phosphate groups,
- The various layers of peptidoglycan are linked by covalent linking of techoic acid to muramic acid to form a mesh
Consequence— The crystal violet color is not allowed to decolorize , so the cells appear blue black
Cell Wall in Gram negative bacteria
- In gram negative bacteria, the cell wall is much thinner with low peptidoglycan concentration but high lipid content.
- Hence the crystal violet gets decolorized when washed due to restraining activity of the mesh like peptidoglycan in gram positive cells.
- Besides, in gram negative bacteria, the outer part of cell wall is high in lipid, polysaccharides and proteins, but there is a space called periplasmic space outside the central membrane external to which is the peptidoglycan followed by the final external membrane
- Thus another stain (counter stain ) becomes very important .
cell in life 