In a standard Gram stain, which color do Gram-positive bacteria appear after completing the 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

In a standard Gram stain, which color do Gram-positive bacteria appear after completing the stain?

Explanation:
During Gram staining, the decisive factor is the cell wall structure. Gram-positive bacteria have a thick peptidoglycan layer that traps the crystal violet-iodine complex and resists decolorization by alcohol, so they remain stained. Once the counterstain is applied, these cells still appear purple because the violet color is retained. Gram-negative bacteria, with a thinner peptidoglycan layer and an outer membrane, lose the crystal violet during decolorization and take up the counterstain, turning pink. Therefore, after completing the stain, Gram-positive bacteria appear purple.

During Gram staining, the decisive factor is the cell wall structure. Gram-positive bacteria have a thick peptidoglycan layer that traps the crystal violet-iodine complex and resists decolorization by alcohol, so they remain stained. Once the counterstain is applied, these cells still appear purple because the violet color is retained. Gram-negative bacteria, with a thinner peptidoglycan layer and an outer membrane, lose the crystal violet during decolorization and take up the counterstain, turning pink. Therefore, after completing the stain, Gram-positive bacteria appear purple.

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