Why do Gram-positive bacteria retain the crystal violet stain but Gram-negative bacteria do not during Gram staining?
Show answer and explanation
Correct answer: Alcohol dissolves the gram-negative outer membrane
During decolorization, alcohol/acetone disrupts the outer membrane of Gram-negative bacteria, making the thin peptidoglycan layer unable to retain the crystal violet–iodine complex. Gram-positive bacteria have thick peptidoglycan that traps the dye.
Practice all 17 Bacteria: Structure and Pathogenesis questions
Keep practicing
More Bacteria: Structure and Pathogenesis questions
- Which bacteria lack a typical cell wall and are therefore not classified by Gram stain?
- Which of the following enables bacterial motility and chemotaxis in many pathogens?
- What is the primary role of lipopolysaccharide (LPS) in Gram-negative bacteria in pathogenesis?
- During biofilm formation by Pseudomonas aeruginosa, which intracellular signaling molecule increases to promote sessile community formation?
- Which structural feature allows Gram-positive bacteria to survive harsh environmental conditions without an outer membrane?
- Which bacterial surface appendage is primarily involved in attachment to host tissues rather than motility?