Structures of the O4 and O18 antigens of Stenotrophomonas maltophilia: a case of enantiomeric repeating units Original Research Article

The O-specific side-chain polymers of lipopolysaccharides from the reference strains for Stenotrophomonas maltophilia serogroups O4 and O18 are both xylosylated rhamnans. In the O4 polymer, both sugar components are the d isomers, whereas the O18 polymer contains only the l isomers. By means of NMR spectroscopy, methylation analysis and Smith degradation, the repeating unit of the O4 polymer was identified as a doubly-branched pentasaccharide of the structure shown below. The O18 polymer is based on the enantiomeric pentasaccharide, but the xylosyl substituent at the 4-position is apparently absent from some units. The polymers closely resemble the O antigens found in Xanthomonas campestris pathovars.