Question

Gram Staining

Answer 1

• Gram staining is a method to differentiate bacteria on the basis of cell wall. It was developed by Hans Christian Gram.
• Method:

  Fix cells on slide. Apply primary stain (crystal violet). All cells will turn purple. Apply iodine (mordant). Apply ethanol (decoloriser ). Apply counter stain : safranin. Cells which become pinkish are gram negative. Cells which retain purple colour are gram positive.

• Gram positive bacteria have thick layer of peptidoglycan in cell wall which resists decoloration by ethanol and thus retains primary purple/violet stain.

• Gram negative bacteria have very thin peptidoglycan layer and is unable to resist decoloration. Thus it loses purple stain and gets stained by counter stain and appear pinkish /reddish.