In Gram negative bacteria, the outer membrane is covered by lipopolysaccharides. The lipopolysaccharides consist of complex polysaccharides covalently linked to lipid A. Lipid A has endotoxin properties, while the polysaccharides have antigenic properties. The envelope of Gram-positive bacteria consists of a peptidoglycan wall, underlying, which is the cytoplasmic membrane. Associated with the peptidoglycan are phosphorus containing acidic polymer called teichoic acids, acidic polysaccharides such as teichuronic acids.