Gram Stain

Gram Staining

Gram staining, also called Gram's Method, is named after Hans Christian Gram who developed the method in 1884, which allows for one to distinguish between gram-postive and gram-negative bacteria using a combination of different chemical stains.  In this test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan. In contrast, negative bacteria do not retain the violet dye and appear as red/pink.