Gram-negative bacteria are those bacteria that do not retain crystal violet dye in the Gram staining protocol. Gram-positive bacteria will retain the crystal violet dye when washed in a decolorizing solution. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria a red or pink color. The test itself is useful in classifying two distinct types of bacteria based on structural differences in...
"Gram-positive bacteria are those that retain a crystal violet dye during the Gram stain process. Gram-positive bacteria appear blue or violet under a microscope, while Gram-negative bacteria appear red or...