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Question

Find the INCORRECT statement about Gram staining of bacteria.

This question was previously asked in
SSC Selection Post 2025 Graduate Level Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

Gram positive bacteria have a thick peptidoglycan layer so they are unable to retain crystal violet

Gram-positive bacteria have a thick peptidoglycan cell wall that holds the crystal violet–iodine complex, so they stay purple. Saying they are unable to retain crystal violet is incorrect.

Gram-negative bacteria have a thin peptidoglycan layer, lose the stain during decolourisation and take up the red/pink counterstain safranin, and Gram's iodine acts as the mordant that forms the complex.

Hence, Gram positive bacteria have a thick peptidoglycan layer so they are unable to retain crystal violet.

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