Structure of the capsular polysaccharide of the KPC-2-producing Klebsiella pneumoniae strain KK207-2 and assignment of the glycosyltransferases functions

Klebsiella pneumoniae strain KK207-2 was isolated in 2010 froma bloodstreaminfection of an inpatient at an Italian hospital. It was previously found to produce the KPC-2 carbapenemase and to belong to clade 1 of sequence type 258. Genotyping of the conserved wzi and wzc genes from strain KK207-2 yielded contrasting results: the wzc-based method assigned the cps207–2 to a new K-type, while the wzi-based method assigned it to the known K41 K-type. In order to resolve this contradiction, the capsular polysaccharide of K. pneumoniae KK207-2 was purified and its structure determined by using GLC-MS of appropriate carbohydrate derivatives, ESI-MS of both partial hydrolysis and Smith degradation derived oligosaccharides, andNMR spectroscopy of oligosaccharides, and the lithium degraded, native and de-O-acetylated polysaccharide. All the collected data demonstrated the following repeating unit for the K. pneumoniae KK207-2 capsular polysaccharide: OAc 6 [3)-β-D-Gal-(1-4)-β-D-Glc-(1-]n 4 I 1 β-D-Glcp-(1-6)-α-D-Glcp-(1-4)-β-D-GlcpA-(1-6)-α-D-Glcp The polysaccharide contains about 0.60 acetyl groups per repeating unit on C6 of the Gal residue. The reactions catalysed by each glycosyltransferase in the cpsKK207-2 gene cluster were assigned on the basis of structural homology with other Klebsiella K antigens.