Gramnegatívoknál

Gramnegatívoknál refers to bacteria that do not retain the crystal violet stain during the Gram staining procedure. This differential staining technique is a fundamental tool in microbiology for classifying bacteria. Gram-negative bacteria, upon completion of the Gram stain, appear pink or red under a microscope because they are decolorized by alcohol and then counterstained with safranin.

The key characteristic differentiating Gram-negative from Gram-positive bacteria lies in their cell wall structure. Gram-negative bacteria possess a thinner peptidoglycan layer compared to Gram-positive bacteria. Crucially, they also have an outer membrane external to the peptidoglycan layer. This outer membrane is composed of a lipid bilayer containing lipopolysaccharides (LPS), phospholipids, and proteins. The LPS layer, in particular, is a significant component and can act as an endotoxin, contributing to the pathogenicity of many Gram-negative organisms.

The presence of this outer membrane serves as an effective barrier, making Gram-negative bacteria generally more resistant to certain antibiotics, dyes, and lysozyme compared to Gram-positive bacteria. Their cell wall structure is also important in their interaction with the host immune system. Many common and medically significant bacteria, such as Escherichia coli, Salmonella, Shigella, Pseudomonas, and Neisseria, are Gram-negative. Their identification and classification are essential for diagnosis, treatment, and understanding infectious diseases.