Understanding the Gram Stain: A Powerful Microbiological Technique for Bacterial Identification in Clinical Laboratories

who created the gram stain, what does it do, and what are the possible results/colors?

Hans Christian Gram, used for ID purposes, staining method that distinguishes between two different kinds of cell walls. (positive= purple; negative=red)

The Gram stain was invented by Danish bacteriologist Hans Christian Gram in 1884. The Gram stain is a microbiological technique used to differentiate bacterial species into two groups based on structural differences in the cell wall. This technique is widely used in clinical laboratories for the identification of bacteria and for preliminary diagnosis of infectious diseases.

The Gram stain procedure involves the use of crystal violet, iodine, alcohol, and safranin. The cells are first stained with crystal violet, followed by iodine. The iodine acts as a mordant, helping to fix the stain to the cell wall. Then, the slide is washed with alcohol to decolorize the cells. Gram-positive cells retain the stain, while Gram-negative cells do not. Finally, the cells are stained with safranin, which functions as a counterstain.

The potential results/colors of the Gram stain are either purple or blue for Gram-positive bacteria and pink or red for Gram-negative bacteria. The color difference is because of the structural differences in the cell wall. Gram-positive bacteria have a thick peptidoglycan layer, which retains the crystal violet stain and appears purple or blue under a microscope. In contrast, Gram-negative bacteria have a thin peptidoglycan layer, along with an outer membrane that is dissolved by alcohol in the decolorization step, resulting in the cells losing the crystal violet stain and appearing pink or red when stained with safranin.

More Answers: