Gram-negative bacteria

Gram-negative bacteria have a thin peptidoglycan layer between inner and outer membranes. Their envelope structure causes them to lose the primary dye during Gram staining and take up the counterstain.

Peptidoglycan: A mesh-like polymer of sugars and amino acids that provides structural strength to most bacterial cell walls. Its thin layer lies between the inner and outer membranes.
Gram stain: A differential staining method that classifies bacteria by how their cell envelopes retain dyes during decolorization. The outer membrane and thin wall let these cells lose crystal violet and take up counterstain.
Enterobacterales: An order of mostly rod-shaped Gram-negative bacteria that includes many intestinal species and important pathogens. Its members include common causes of urinary, bloodstream, and gastrointestinal infections.
Sepsis: A life-threatening condition caused by a dysregulated response to infection that leads to organ dysfunction. Severe Gram-negative infections can trigger sepsis through bacterial products and host inflammation.
Outer membrane: A lipid bilayer found outside the cell wall in some bacteria, containing proteins and lipopolysaccharide. This additional barrier is a defining feature of the Gram-negative envelope.
Bacterial cell envelope: The layers surrounding a bacterial cytoplasm, including the cell membrane and, in many species, a cell wall. Gram-negative architecture is one distinctive arrangement of envelope layers.
Pseudomonas aeruginosa: A Gram-negative bacterium that can cause opportunistic infections, especially in hospitalized or immunocompromised people. Its intrinsic resistance and ability to thrive in moist settings complicate treatment.
Antimicrobial peptide: A small molecule produced by organisms that can kill microbes or inhibit their growth. The outer membrane helps determine susceptibility to host-defense peptides.
Lipopolysaccharide: A major outer-membrane component composed of lipid A, a core oligosaccharide, and an O antigen. Its lipid A portion can trigger strong inflammatory responses during infection.
Lipid bilayer: A double layer of amphipathic lipids that forms the basic structure of biological membranes. The inner membrane and outer membrane are both lipid bilayers with different compositions.

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