Gram-negative bacteria are a group of bacteria that possess a cell envelope composed of a thin layer of peptidoglycan surrounded by an outer membrane. This outer membrane contains lipopolysaccharides (LPS), which contribute to the characteristic properties of Gram-negative bacteria.
During the Gram staining procedure, Gram-negative bacteria do not retain the crystal violet stain well due to the presence of the outer membrane, causing them to appear pink or red when viewed under a microscope after counterstaining with safranin.
Gram-negative bacteria are known for their resistance to many antibiotics due to the presence of the outer membrane, which acts as a barrier to the entry of certain drugs. Additionally, they can cause severe infections in humans and animals due to the release of endotoxins from the LPS layer.
Many medically important bacteria belong to the Gram-negative group, including Escherichia coli, Salmonella spp., Pseudomonas aeruginosa, Neisseria gonorrhoeae, and Haemophilus influenzae.
Understanding the Gram-negative classification is crucial in microbiology for bacterial identification, antibiotic selection, and understanding bacterial pathogenesis.