Gramvärjäykselle

Gramvärjäykselle is a staining technique used in microscopy to differentiate bacterial species into two large groups: Gram-positive and Gram-negative. Developed by Danish bacteriologist Hans Christian Gram in 1884, the method relies on differences in the cell wall composition of bacteria.

The procedure involves treating a heat-fixed sample of bacteria with a primary stain, typically crystal violet. This stain enters all bacterial cells. Next, a mordant, usually iodine, is applied. Iodine forms a complex with the crystal violet, making it less soluble. The slide is then decolorized with a solvent such as alcohol or acetone. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall that retains the crystal violet-iodine complex, appearing purple or blue under the microscope. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane. The decolorizer washes out the crystal violet-iodine complex from these cells. Finally, a counterstain, such as safranin or basic fuchsin, is applied. This stains the decolorized Gram-negative bacteria pink or red.

The Gram stain is a fundamental tool in microbiology for initial bacterial identification and classification. It is crucial in clinical settings for diagnosing infections and guiding antibiotic treatment, as many antibiotics target specific cell wall components. Variations in the Gram stain result can indicate important biological differences between bacteria, affecting their pathogenicity and response to antimicrobial agents.