Which color do Gram-negative enteric bacteria typically appear after the safranin counterstain?

• A. Pale pink
• B. Dark violet
• C. Purple
• D. Blue

Answer: (A)

Staining outcome hinges on cell wall structure. Gram-negative enteric bacteria have a thin peptidoglycan layer and an outer membrane, so during the decolorization step the crystal violet-iodine complex is washed away and these cells become colorless. When the safranin counterstain is applied, they take up the pinkish dye, resulting in a pale pink appearance under the microscope. This contrasts with Gram-positive bacteria, which retain the dark purple crystal violet due to their thick peptidoglycan layer, so they don’t take on the counterstain as strongly. Blue isn’t the typical result of this Gram stain protocol. Pale pink is the expected color after counterstaining Gram-negative enteric bacteria.