gramfärgning

Gramfärgning, also known as gram staining, is a method of differentiating bacterial species into two groups based on the characteristics of their cell walls. This technique was developed by the Danish bacteriologist Hans Christian Gram in 1884 and remains a fundamental tool in microbiology.

The process involves staining bacterial cells with a primary dye, typically crystal violet, followed by treatment with a mordant, such as iodine. The cells are then washed with alcohol or acetone, which acts as a decolorizing agent. After this step, a counterstain, such as safranin or fuchsine, is applied. The differential staining results from the varying permeability of the cell walls to the decolorizing agent.

Bacteria are categorized as either gram-positive or gram-negative based on their response to the gram stain. Gram-positive bacteria retain the primary stain and appear purple or blue under a microscope. This group includes organisms like Staphylococcus and Streptococcus. Gram-negative bacteria, on the other hand, do not retain the primary stain and appear pink or red due to the counterstain. Examples of gram-negative bacteria include Escherichia coli and Pseudomonas aeruginosa.

The difference in staining properties is due to the structure of the bacterial cell walls. Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-iodine complex, while gram-negative bacteria have a thinner peptidoglycan layer surrounded by an outer membrane, which is more susceptible to decolorization.

Gram staining is a crucial technique in clinical microbiology for the preliminary identification of bacterial pathogens and the selection of appropriate antimicrobial therapy. It provides valuable information about the nature of an infection and helps guide treatment decisions.