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GK QUESTION#3933

Identify the incorrect statement regarding the Gram staining technique for bacteria:

  1. AGram-negative bacteria have a thin peptidoglycan layer and do not retain crystal violet
  2. BGram-positive bacteria have a thick peptidoglycan layer and cannot retain crystal violetCorrect answer
  3. CGram’s iodine helps form the crystal-violet–iodine complex
  4. DGram-negative bacteria appear red or pink under a microscope
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Answer

B. Gram-positive bacteria have a thick peptidoglycan layer and cannot retain crystal violet

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Explanation

Statement B is incorrect. After a correctly completed Gram stain, thick-walled Gram-positive bacteria retain the crystal-violet–iodine complex and appear purple. Gram-negative cells lose this complex during decolorization and take up the pink or red counterstain.

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