Question

Staining material of gram positive bacterium is

• A. Fast green
• B. Haematoxylin
• C. Crystal violet
• D. Safranin

Hint:

Crystal violet is the primary stain used in Gram staining, which helps differentiate Gram-positive bacteria from Gram-negative bacteria.

Answer 1

The Correct Option is C

In Gram staining, crystal violet is applied first and forms a complex with iodine inside the cell. Gram-positive bacteria, with their thick peptidoglycan cell wall, trap this crystal violet-iodine complex even after the decolorizing step, retaining the purple color, whereas Gram-negative bacteria lose it and must be counterstained with safranin to become visible. This makes crystal violet the stain specifically associated with gram-positive bacteria's appearance under the microscope.

Therefore, the correct answer is Crystal violet.

Answer 2

Another way to approach this is to walk through the Gram staining procedure step by step and note which dye corresponds to which stage.

1. Fast green: This dye does not appear at any stage of the standard Gram staining sequence.
2. Haematoxylin: This dye also does not feature in the Gram staining protocol, being used instead in general histological nuclear staining.
3. Crystal violet: Applied as the very first stain in the sequence, this dye is what remains trapped in Gram-positive cell walls after iodine fixation, alcohol decolorization, and the final counterstain step, giving these bacteria their purple appearance.
4. Safranin: Applied last, this dye only becomes visible in bacteria that already lost the crystal violet, meaning it colors Gram-negative, not Gram-positive, bacteria.

Tracing the staining sequence confirms that the dye retained by gram-positive bacteria is crystal violet.

Therefore, the correct answer is Crystal violet.