Gramvärjäyksillä

Gramvärjäyksillä, often translated as Gram staining, is a fundamental differential staining technique used in microbiology to classify bacteria into two large groups based on their cell wall composition: Gram-positive and Gram-negative. The method was developed by Danish bacteriologist Hans Christian Gram in 1884.

The procedure involves applying a primary stain, crystal violet, to a heat-fixed bacterial smear. This is followed by the addition of a mordant, usually Gram's iodine solution, which forms a complex with the crystal violet, trapping it within the cell. Decolorization with an alcohol or acetone-alcohol mixture is then performed. Gram-positive bacteria retain the crystal violet-iodine complex, appearing purple or blue. Gram-negative bacteria, having a thinner peptidoglycan layer and an outer membrane, lose the crystal violet-iodine complex during decolorization and are subsequently counterstained with safranin, a red or pink dye.

The difference in retention of the primary stain is attributed to variations in the structure of the bacterial cell wall. Gram-positive bacteria have a thick peptidoglycan layer that dehydrates and shrinks in the presence of the decolorizing agent, trapping the crystal violet-iodine complex. Conversely, Gram-negative bacteria have a thinner peptidoglycan layer and a lipid-rich outer membrane. The decolorizing agent dissolves this outer membrane and washes the crystal violet-iodine complex from the thin peptidoglycan layer.

Gram staining is a crucial initial step in the identification and classification of bacteria. It provides rapid preliminary information about the morphology and Gram reaction of a sample, guiding subsequent diagnostic and treatment decisions, particularly in clinical microbiology.