Structure of the O-7 antigen from Acinetobacter baumannii

The polymeric O-antigen was isolated from the lipopolysaccharide of the reference strain for Acinetobacter baumannii serogroup O-7. Both the lipopolysaccharide and the isolated polymer reacted with the homologous antiserum. Monosaccharide analyses and NMR spectra showed that the polymer had a hexasaccharide repeating unit constructed from residues of l-rhamnose (4) and N-acetyl-d-glucosamine (2). The following structure for the repeating unit was established by means of detailed interpretation of the NMR spectra, methylation analysis, and chemical degradations. The tetrasaccharide backbone is identical to that for the O-10 antigen of A. baumannii, which has α-d-ManpNAc as the lateral substituent in place of the disaccharide p