Bacterial outer membrane lipid A and associated membrane phospholipids (Lipid A)

Lipid A is a highly conserved glycolipid component that serves as the hydrophobic anchor of lipopolysaccharide (LPS) within the outer membrane of Gram-negative bacteria (Raetz & Whitfield, 2002). It is often referred to as endotoxin because it is the primary moiety responsible for the potent inflammatory response and toxic effects associated with Gram-negative infections via TLR4 activation (Beutler & Rietschel, 2003). Along with associated membrane phospholipids like phosphatidylethanolamine and phosphatidylglycerol, Lipid A maintains the structural integrity and selective permeability of the bacterial cell envelope (Nikaido, 2003). This target is clinically significant as the primary binding site for polymyxin antibiotics, such as colistin and polymyxin B (Poirel et al., 2017). These drugs interact electrostatically with the negatively charged phosphate groups of Lipid A, displacing stabilizing divalent cations and leading to membrane disruption and cell death (Trimble et al., 2016). However, modifications to Lipid A, such as the addition of 4-amino-4-deoxy-L-arabinose, represent a major mechanism of bacterial resistance (Baron et al., 2016).

Other names

EndotoxinLipopolysaccharide anchorLPS Lipid AGram-negative outer membrane lipids

Polymyxins bind to the negatively charged phosphate groups of lipid A and associated phospholipids through electrostatic interactions, displacing divalent cations (Mg2+ and Ca2+) that stabilize the outer membrane (StatPearls, 2023). This leads to increased membrane permeability, leakage of intracellular contents, and ultimately bacterial cell death (PubMed, PMID: 27337121).