Gramnégatives

Gramnégatives refers to a group of bacteria that do not retain the crystal violet stain used in the Gram staining procedure. Instead, they are decolorized by alcohol and then take up the counterstain, safranin, appearing pink or red under a microscope. This differential staining characteristic is due to a thinner peptidoglycan layer in their cell walls and the presence of an outer membrane, which is more permeable to the decolorizing agent.

The outer membrane of Gram-negative bacteria contains lipopolysaccharides (LPS), which are also known as endotoxins. These endotoxins can trigger a strong immune response in humans and animals, leading to symptoms such as fever, inflammation, and shock. Examples of common Gram-negative bacteria include Escherichia coli, Salmonella, Shigella, Pseudomonas aeruginosa, and Neisseria gonorrhoeae.

Many Gram-negative bacteria are opportunistic pathogens, meaning they can cause disease when the host's defenses are compromised. They are responsible for a wide range of infections, including urinary tract infections, pneumonia, meningitis, and gastrointestinal illnesses. Understanding the Gram-negative classification is crucial in microbiology for identifying bacteria, diagnosing infections, and selecting appropriate antibiotic treatments, as many antibiotics are effective against Gram-negative bacteria but not Gram-positive ones, and vice versa.