What is the role of iodine in the Gram stain?

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Prepare for the WGU NURS1010 Microbiology Exam with engaging study materials, flashcards, and multiple choice questions. Enhance your understanding with detailed explanations and insights. Get exam-ready today!

Multiple Choice

What is the role of iodine in the Gram stain?

Explanation:
Iodine acts as a mordant in the Gram stain. It binds with the crystal violet to form a crystal violet–iodine complex that is large and less soluble. This complex is trapped inside the cell wall, especially in Gram-positive bacteria with a thick peptidoglycan layer, so the purple stain is retained during the decolorization step. In Gram-negative bacteria, the CV–I complex is more easily washed out by the alcohol decolorizer, so they appear colorless until the counterstain is applied. Iodine is not the fixative to the slide, not the decolorizer, and not the counterstain.

Iodine acts as a mordant in the Gram stain. It binds with the crystal violet to form a crystal violet–iodine complex that is large and less soluble. This complex is trapped inside the cell wall, especially in Gram-positive bacteria with a thick peptidoglycan layer, so the purple stain is retained during the decolorization step. In Gram-negative bacteria, the CV–I complex is more easily washed out by the alcohol decolorizer, so they appear colorless until the counterstain is applied. Iodine is not the fixative to the slide, not the decolorizer, and not the counterstain.

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