Structure of the K49 capsular polysaccharide produced by the Acinetobacter baumannii ST10 carriage isolate, NL6

The K49 capsular polysaccharide (CPS) produced by the Acinetobacter baumannii ST10 carriage isolate, NL6, that carries KL49 at the CPS biosynthesis K locus, was studied by sugar analysis along with one- and two-dimensional ¹H and ¹³C NMR spectroscopy. The CPS was found to be comprised of linear trisaccharide units that include 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-d-galacto-non-2-ulosonic acid (5,7-di-N-acetyl-8-epilegionaminic acid; 8eLeg5Ac7Ac), l-FucpNAc and d-GlcpNAc residues. The genetic analysis identified α-d-GlcpNAc as the first sugar, revealing that the 8eLeg5Ac7Ac-(2→3)-α-l-FucpNAc-(1→3)-α-d-GlcpNAc units are linked by Wzy_KL49 to form an α-GlcpNAc-(1→8)-8eLeg5Ac7Ac linkage. In addition, while KL49 includes two initiating transferase genes, NL6 harbours an ISAba1 interruption in itrB2 indicating that ItrB2, the second initiating transferase that was thought to be redundant, is not needed to make the K49 CPS. The CPS composition was found to be identical to that of a previously reported undefined polysaccharide recovered from A. baumannii ST10 isolate, LAC-4, that has since been shown to carry KL49. Hence, this polysaccharide is also a CPS.