Question

Gram staining technique is based on the fact that Gram-positive bacteria retain _______ stain that Gram-negative bacteria do not.

• A. Safranin
• B. Crystal violet
• C. Acetone
• D. Phenol

Answer 1

The correct option is B Crystal violet

Hans Christian Gram figured out that based on the amount of peptidoglycan content in the bacterial cell walls, bacteria react to crystal violet dye differently. He used this method to broadly classify bacteria into gram-positive - that is bacteria having thick cell walls and retain the crystal violet stain or gram stain even when washed with acetone, and the gram-negative bacteria, which are bacteria with thinner cell walls and do not retain the crystal violet dye.
Safranin is a counterstain that only Gram-negative bacteria take up.
Phenol and acetone are not stains.