Gram-positive bacteria are
bacteria that give a positive result in the
Gram stain test. Gram-positive bacteria take up the
crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. This is because the thick
peptidoglycan layer in the bacterial
cell wall retains the
stain after it is washed away from the rest of the sample, in the decolorization stage of the test.