Which statement correctly describes Gram-negative bacteria in Gram staining?

Which statement correctly describes Gram-negative bacteria in Gram staining?

• A. They stain pink due to safranin
• B. They stain purple due to crystal violet
• C. They stain colorless
• D. They stain blue due to methylene blue

Answer: (D)

During Gram staining, Gram-negative bacteria end up pink because the alcohol-based decolorizer disrupts their outer membrane and thin peptidoglycan, washing away the crystal violet-iodine complex. The subsequent counterstain, safranin, then binds to the now colorless cells, giving them a pink color. In contrast, Gram-positive bacteria retain the purple crystal violet-iodine complex due to their thick peptidoglycan layer, so they appear purple. Colors like colorless would occur if no counterstain were applied, and blue from methylene blue isn’t part of this staining scheme.

During Gram staining, Gram-negative bacteria end up pink because the alcohol-based decolorizer disrupts their outer membrane and thin peptidoglycan, washing away the crystal violet-iodine complex. The subsequent counterstain, safranin, then binds to the now colorless cells, giving them a pink color. In contrast, Gram-positive bacteria retain the purple crystal violet-iodine complex due to their thick peptidoglycan layer, so they appear purple. Colors like colorless would occur if no counterstain were applied, and blue from methylene blue isn’t part of this staining scheme.