Final answer:
Gram-negative bacteria appear pink after the Gram stain process due to their cell wall structure and the presence of an outer membrane.
Step-by-step explanation:
The Gram stain process is a commonly used technique in microbiology to differentiate between Gram-positive and Gram-negative bacteria. Gram-positive bacteria appear purple after the staining process whereas Gram-negative bacteria appear pink. There are two main reasons why Gram-negative bacteria appear pink when stained:
- Cell wall structure: Gram-negative bacteria have a thinner peptidoglycan layer in their cell walls, which allows the crystal violet stain to be washed out more easily during the decolorizing step of the staining process. This leads to the pink coloration with the counterstain, safranin.
- Outer membrane: Gram-negative bacteria have an additional outer membrane that Gram-positive bacteria lack. This outer membrane acts as a barrier and prevents the crystal violet stain from fully penetrating into the cell wall. As a result, the pink counterstain, safranin, becomes more prominent.