Schematic structures of the LOS moieties on the surface of M. catarrhalis and the proposed LOS structures of M. catarrhalis serotype A strain O35E and its mutants, O35Elgt5 and O35EgalE. Three main serotypes, A, B and C, are presented with different R groups (A) [18, 19, 25, 26]. One- or two-Gal-residue deletion on the O35Elgt5 or the O35EgalE LOS branch is displayed, respectively (B) [27–29]. Abbreviations: Gal, galactose; Kdo, 3-deoxy-D-manno-octulosonic acid; Glc, glucose; GlcNAc, N-acetyl-D-glucosamine; p, pyranose.