What color do gram-negative bacteria appear after the gram staining process?

Gram-negative bacteria appear pinkish-red after the gram staining process due to their cell wall structure. In this process, a primary stain (crystal violet) is applied first, which stains all bacteria initially. After that, a mordant (iodine) is added, which forms a complex with the crystal violet in the cells. The next step involves decolorization using alcohol or acetone, which disrupts the outer membrane and allows the crystal violet-iodine complex to leach out of gram-negative bacteria that have a thinner peptidoglycan layer.

Once decolorization has occurred, a counterstain (safranin) is applied. Gram-negative bacteria take up this counterstain, appearing pinkish-red under the microscope. This characteristic color is essential for differentiating between gram-negative and gram-positive bacteria, as the latter retains the crystal violet stain due to their thicker cell walls, appearing bluish-purple. Thus, understanding the gram staining process is crucial for microbiology, as it helps in the identification and treatment of bacterial infections.