Gram Stain Gram Stain



Gramstaining refers to the method of categorizing bacterial species intotwo major groups gram-positive and gram-negative. Gram methoddifferentiates bacteria by the physical and chemical features oftheir cell walls by identifying peptidoglycan, contained in a thicklayer in gram-positive bacteria (Black,2012).The name of the procedure was derived from the inventor HansChristian Gram.

Gramstain procedure

Inthe Gram stain procedure, the cells to be tested are first heatfixed, stained with a standard dye, crystal violet. The dye is takenup in equal proportions by the bacteria. The slides are treated withmordant (I2-KI mixture) to fix the stain. Then they are destainedwith 95 percent of alcohol and later counterstained with a lessintense dye of a variant color. Gram-positive bacteria maintain thecrystal violet dye, whereas the counterstain added after the crystalviolent, decolorizes giving the gram-negative bacteria a pink or redcoloration (Black,2012).Basically, the difference between gram-positive and gram negativebacteria is the capability of the cell wall of the organism tomaintain the violet color.

Significanceof Grain Stain

Gramstaining is very significant in microbiology as it is usually thefirst step in the identification of a bacterial organism. Even thoughit is a valuable method in microbiology, not all bacteria can bedistinctively classified using this approach. Nevertheless, itsadvent made it easy to categorize bacteria into variousclassifications.

HowGram stain changed our understanding of microbiology?

Gramstaining did not only allow differentiation of different bacteria,but also made it possible for bacteria in a given tissue or surfaceto be elaborately identified. The technique also brought aboutunderstanding of the differences in the cell walls of differentbacteria (Black,2012).In addition, the technique revealed another perspective ofgram-positive and gram-negative bacteria. For instance, the walls ofgram-positive bacteria when damaged can make the bacteria appear asgram-negative.


Black,J. G. (2012). MicrobiologyPrinciples and Explorations 8th edition.Wiley.