What color indicates gram-negative bacteria in the Gram staining process?

In the Gram staining process, gram-negative bacteria are indicated by a red color after being subjected to the staining technique. This staining process involves several steps, including the application of a crystal violet stain, followed by iodine, which forms a complex with the crystal violet. After this, a decolorizer, often alcohol or acetone, is applied.

For gram-negative bacteria, the outer membrane is disrupted by the decolorizer, allowing the crystal violet-iodine complex to wash away. After decolorization, a counterstain, usually safranin, is applied. Gram-negative bacteria will take up this counterstain, appearing red or pink, distinguishing them from gram-positive bacteria, which retain the crystal violet and appear blue or purple. Thus, red correctly identifies gram-negative bacteria due to their structural characteristics and how they respond to the staining process.