Why does Pseudomonas aeruginosa appear pink after the counterstain is added?

Explanation:

Pseudomonas aeruginosa is a Gram-negative bacterium that does not retain the crystal violet stain in the Gram staining process due to its thin peptidoglycan layer. Instead, it takes up the pink safranin counterstain. Thus, Pseudomonas aeruginosa will appear pink after the counterstain is added.

The question is about the Gram staining process of the bacterium Pseudomonas aeruginosa. In this process, bacterial cells are stained with crystal violet dye and then decolorized with alcohol or an acetone/alcohol solution. After decolorization, a counterstain, often safranin, is added. Based on how these dyes interact with the peptidoglycan layer in bacterial cell walls, cells will either retain the crystal violet dye, appearing purple (gram-positive), or take up the counterstain, appearing pink (gram-negative).

Typically, Pseudomonas aeruginosa is a Gram-negative bacterium. This means that it does not retain the crystal violet stain due to its thin peptidoglycan layer and is instead colored by the pink safranin counterstain. Therefore, after the counterstain is added, Pseudomonas aeruginosa will appear pink.