Structure of a new pseudaminic acid-containing capsular polysaccharide of Acinetobacter baumannii LUH5550 having the KL42 capsule biosynthesis locus

•Capsular polysaccharide was isolated from Acinetobacter baumannii LUH5550.•The polysaccharide contains 5-N-acetyl-7-N-[(R)-3-hydroxybutanoyl]pseudaminic acid.•Structure of the polysaccharide was established by NMR and chemical approaches.•Capsule biosynthesis locus was analyzed and found to match the structure established.

The capsular polysaccharide from Acinetobacter baumannii LUH5550 was studied by 1D and 2D 1H and 13C NMR spectroscopy. The following structure of the branched trisaccharide repeating unit was established:where Pse5Ac7RHb indicates 5-acetamido-3,5,7,9-tetradeoxy-7-[(R)-3-hydroxybutanoylamino]-l-glycero-l-manno-non-2-ulosonic acid. The genes in the capsule biosynthesis locus designated KL42 are consistent with the structure established.

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