Describe the purpose of each of the four basic steps of Gram

Describe the purpose of each of the four basic steps of Gram staining.

Solution

Gram Staining: It is used to differentiate gram positive and gram negative bacteria. It differentiates bacteria on the bases of cell wall characteristics, that is presence or absence of peptidoglycan. Gram positive bacteria contains major portion of peptidoglycan in cell wall.

Four basic steps of Gram staining are as follows:

When bacteria stained with crystal violet, gram positive bacteria stained blue, iodine solutions help in trapping the dye (crystal violet). Gram negative bacteria have very low amount of peptidoglycan as compare to gram negative bacteria. The blue color of gram positive bacteria cannot be decolorized after acetone or ethanol treatment whereas gram negative bacteria lose its blue color in decolonization step. In counter staining with safranin gram negative bacteria gain pink/ red color where on gram positive bacteria pink color is not visible because of dark blue color of crystal violet. Therefore after gram staining gram positive bacteria appear blue and gram negative bacteria appears pink/red under microscope.