Pseudomonas aeruginosa is a Gram-negative bacterium widely distributed in nature and causing opportunistic infections in humans. P. aeruginosa is an important bacterial pathogen of nosocomial (hospital derived) infections, and it can also cause life threatening diseases in patients with cancer, burn wounds, cystic fibrosis and those that have received immunosuppressive therapy. Lipopolysaccharide (LPS) is an integral component of the P. aeruginosa cell envelope, occupying the outer leaflet of the outer membrane in this pathogen. The LPS inner core OS sugar composition in P. aeruginosa is identical among P. aeruginosa strains and it consists of two residues of 3-deoxy-d-manno-octulosonic acid (KdoI and KdoII) and two residues of L-glycero-d-manno-heptose (HepI and HepII). The high degree of phosphorylation of the inner core is essential for viability of P. aeruginosa.