Gram +ve bacteria on treatment with crystal violet dye give _________colour?

Correct answer: C. purple

  • A. red
  • B. green
  • C. purple
  • D. pink

Explanation

Gram-positive bacteria retain the crystal violet-iodine complex because their thick peptidoglycan wall is not decolorized by alcohol, so they appear purple. Gram-negative bacteria lose the crystal violet and later take the counterstain, so students may choose red or pink by mixing up the two Gram reactions.

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