Which component of the Gram stain do Gram-negative bacteria retain?

Which component of the Gram stain do Gram-negative bacteria retain?

• A. Crystal violet
• B. Iodine solution
• C. Decolorizer
• D. Safranin

Answer: (D)

Differential staining separates bacteria by cell wall structure. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane; when the decolorizer (ethanol/acetone) is applied, it disrupts this outer membrane and washes the crystal violet-iodine complex out. The cells become colorless at that stage, so they take up the counterstain. Safranin is the counterstain, and these Gram-negative cells absorb it, appearing pink/red under the microscope. So Gram-negative bacteria retain the counterstain safranin.

Differential staining separates bacteria by cell wall structure. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane; when the decolorizer (ethanol/acetone) is applied, it disrupts this outer membrane and washes the crystal violet-iodine complex out. The cells become colorless at that stage, so they take up the counterstain. Safranin is the counterstain, and these Gram-negative cells absorb it, appearing pink/red under the microscope. So Gram-negative bacteria retain the counterstain safranin.