Gramvärjäykseen

Gramvärjäys, also known as Gram staining, is a differential staining technique used in microbiology to classify bacteria into two major groups: Gram-positive and Gram-negative. Developed by Danish physician Hans Christian Gram in 1884, the method relies on the chemical and physical properties of bacterial cell walls.

The process involves applying a primary stain, typically crystal violet, to a heat-fixed bacterial smear. This is followed by the addition of a mordant, usually Gram's iodine, which forms a complex with the crystal violet. The smear is then decolorized with a solvent, such as ethanol or acetone. Gram-positive bacteria, with their thick peptidoglycan layer, retain the crystal violet-iodine complex and appear purple or blue under a microscope. In contrast, Gram-negative bacteria, which have a thinner peptidoglycan layer and an outer membrane, lose the primary stain during decolorization. Finally, a counterstain, such as safranin, is applied, which stains the decolorized Gram-negative bacteria pink or red.

The Gram stain is a crucial initial step in the identification of bacteria, providing rapid and valuable information about cell wall composition. This distinction helps in selecting appropriate antimicrobial treatments, as Gram-positive and Gram-negative bacteria often respond differently to antibiotics. For example, certain antibiotics are more effective against one group than the other. The technique is widely used in clinical laboratories for diagnosing bacterial infections and in research for characterizing unknown bacterial species. Variations of the Gram stain exist, but the fundamental principle of differential staining based on cell wall structure remains consistent.