What color do Gram-Negative bacteria stain?

Gram-negative bacteria stain red or pink because they have a thinner peptidoglycan layer in their cell walls compared to Gram-positive bacteria. During the Gram staining process, these bacteria do not retain the crystal violet dye applied in the first step and are instead counterstained with safranin, which gives them their characteristic red or pink color.

The structural differences in the cell wall between Gram-negative and Gram-positive bacteria play a key role in this staining process. The outer membrane of Gram-negative bacteria contains lipopolysaccharides, which contributes to the inability to hold onto the crystal violet stain during the decolorization step with alcohol or acetone. This is why they adopt the red/pink color after the application of the safranin.

Understanding this staining technique is important in microbiology since it aids in differentiating between types of bacteria, which can influence their pathogenicity and treatment options. The distinct color response helps in identifying bacterial infections and managing appropriate antibiotic therapy.