Question

During the Gram stain, ________ cells decolourise when alcohol is applied

• A. Positive
• B. Negative
• C. Both positive and negative
• D. Neither positive or negative

Answer 1

The correct option is B Negative

Gram-staining is based on the ability of bacteria cell wall to retaining the crystal violet dye during solvent treatment.
The cell walls for Gram-positive microorganisms have a higher peptidoglycan and lower lipid content than gram-negative bacteria.
The cell walls for gram-negative microorganisms have thinner peptidoglycan and higher lipid content than gram-positive bacteria.
The removal of the lipid layer enhances the leaching of the crystal violet stain from the cells into the surrounding solvent. So during gram-stain, the gram-positive bacteria retain the crystal violet while the gram-negative decolourize as the high lipid content in the cell wall is washed away by the alcohol and their peptidoglycan layer is also thin to retain the crystal violet.