Question

1. Describe the difference between gram-positive and gram-negative bacterial cell walls. Explain which stains bind to gram positive and which ones bind to gram negative cells. Which of these bacteria is more susceptible to antibiotics and why?

Answer 1

Primary stain( crystal violet )binds to gram positive and counter-stain(safranin) binds to gram negative bacterial cell walls.As the crystal violet stain gives CV⁺ and Cl^{​​​​​-} ions.CV⁺ ion interact with the bacterial negative cell wall and when Iodine as a mordant uses it complexed with CV⁺ and form large complex of CV-I.Uses of alcohol as decolourisation, dehydration of the wall shrinks and the stain become more compact.

But for gram negative bacteria,the cell wall or peptidoglycan layer is so thin and the pores are less compact.The decolorizar melt the outer lipopolysaccharide layer and wash out the CV-I complex.When after washing with alcohol, safranin uses as counter-stain and the gram negative bacterial cell wall bind to it.

Gram-negative bacteria is more susceptible to antibiotics.

In gram negative bacteria ,there is a extra outer layer at outer surface of the cell wall.It is consist of lipopolysaccharide and different type of protein.The lipid-A chain of lipopolysaccharide contain six saturated fatty acids and provide a more compact structure and the polysaccharide region contain o-antigen which provides a immune response of the bacteria.And the lipopolysaccharide and pore forming protein with size-specific exclusion is more resistant to most antibiotics.