Gram-negative bacterial cells possess two membranes - the inner cytoplasmic membrane and the outer membrane. The two membranes are distinct in their composition; the inner membrane is composed of a phospholipid bilayer, whereas the outer membrane (OM) is composed of an asymmetrical bilayer, with the outer leaflet containing lipopolysaccharide (LPS) (Raetz and Whitfield, 2002). Surface polysaccharides, such as LPS O-antigen, or capsular polysaccharide, are often tightly associated with the OM (Whitfield, 2006). This tight association can be used to generate a rough quantification of surface polysaccharides of Gram-negative bacterial cells, as the OM can easily be dissociated from cells without associated cell lysis (Brimacombe et al., 2013). The following method describes how to quickly extract and quantify OM-associated polysaccharides.
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