Question

The Gram's stains used to stain bacteria are:

• A. Safranin and iodine
• B. Cotton blue and iodine
• C. Crystal violet and safranin
• D. Crystal violet and cotton blue

Answer 1

The correct option is C Crystal violet and safranin

Staining is an accessory technique used in microscopy to enhance contrast in microscopic images. Different coloured stains and dyes are used to highlight biological structures for viewing under the microscope.

Gram staining is one the staining technique which classifies bacteria into two groups as Gram positive and Gram negative. This classification depends upon the chemical and physical properties of cell wall of bacteria.

Gram staining is an important diagnostic tool for clinical and research settings. This staining technique uses two stains as crystal violet as first stain and safranin as counterstain.

Gram positive bacteria retain the crystal violet stain as they possess a thick layer of peptidoglycan (50-90% of their cell envelope) in their cell wall.

Whereas, Gram negative bacteria possess thinner layer of peptidoglycan (10% of their cell envelope) in their cell wall.

Due to this, Gram negative bacteria do not retain crystal violet and allow it to rinse away when rinsed with ethanol.

Gram negative bacteria are stained by the counterstain safranin.

Hence, Gram positive bacteria appear purple and Gram negative bacteria appear pink.