What color corresponds to a "Gram positive" reading in a bacterial test?

In bacterial testing, particularly in Gram staining, a "Gram positive" reading corresponds to a blue or purple color. This outcome indicates that the bacterium has a thick peptidoglycan layer in its cell wall, which retains the crystal violet stain used during the Gram staining process. This retention causes the bacteria to appear blue or purple under a microscope.

The process begins with applying crystal violet dye, followed by a mordant that helps fix the dye in the cells. When decolorized, Gram-positive cells do not lose the dye due to their impermeable thick cell wall, hence they remain stained blue or purple. The distinction between Gram-positive and Gram-negative bacteria is crucial for identification and treatment strategies, as Gram-negative bacteria tend to have a thinner peptidoglycan layer and can appear pink or red after the staining process due to the counterstain (safranin).

The other colors do not correspond to the Geram positive outcome in this context.