GRAM STAINING

Gram staining, one of the most frequently used techniques in microbiology, was developed by a Danish bacteriologist by the name of Hans Christian Gram way back in 1884. It differentiates between Gram-positive and Gram-negative bacteria. This staining method is useful in classifying microorganisms and distinguishing them from one another. In this process, some of the bacteria, stained by the primary stain, Crystal Violet, and fixed with the mordant, retain the primary stain, and some of them get decolorized by alcohol. In gram-positive bacteria, peptidoglycan is layered on the cell walls, and the lipid content is very low. Decolorization leads to the drying and shrinking of the cell wall, closing the pores and blocking the exit of the stain from the cell. The trapped Crystal Violet-Iodine complex appears blue or purple. While Gram-negative bacteria readily absorb the crystalline violet-iodine complex, due to the thin layer of peptidoglycan and thick outer layer of lipids, CV-Iodine complex is washed off. Exposed to alcohol, the decolorizer breaks the lipids in the cell walls and allows the crystal violet-iodine combination to leave the cells. When they are stained again with safranin, they absorb the stain and appear red.





































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