Structure of the O18 antigen from Acinetobacter baumannii

The polymeric O antigen was obtained from lipopolysaccharide extracted from isolated, defatted cell walls of the reference strain for Acinetobacter baumannii serogroup O18. Monosaccharide analyses and NMR spectra established that the polymer had a regular structure with a repeating unit based on residues of d-galactose (2), N-acetyl-d-galactosamine (1), and N-acetyl-d-mannosamine (1). Further interpretation of the NMR spectra, combined with the results of methylation analysis and a Smith degradation, showed that the repeating unit had the following structure.