Structure of LPS in Gram-negative bacteria. LPS consists of three primary regions: lipid A, the polysaccharide core (composed of an inner and outer core), and the O-antigen. The monosaccharides of LPS, polysaccharide core, and O-antigen are represented schematically as hexagons to simplify the structure of the molecule. The inner core is highly conserved among species and is composed of 3-deoxy-d-manno-octulosonic acid (Kdo) (aqua) and heptose (Hep) (purple). The outer core (yellow) and O-antigen (brown) are variable among bacteria. n represents the number of O-antigen repeats, which vary in length depending on the species and can be as large as 40 repeating units. Alterations in the length of the LPS (depicted by the blue dashed lines) result in physical alterations in colony and cell morphology that ranges from smooth to deep rough.