O-antigen of Escherichia coli serotype O25B

The O-antigen of Escherichia coli serotype O25B is a surface-exposed bacterial polysaccharide that constitutes the terminal portion of the lipopolysaccharide (LPS) molecule on the outer membrane of certain E. coli strains, including globally relevant extraintestinal pathogenic E. coli (ExPEC). It is defined by a unique O-acetylated pentasaccharide repeating unit: →4)-[β-D-Glc-(1→6)]-[α-L-Rha-(1→3)]-α-D-Glc-(1→3)-α-L-Rha2Ac-(1→3)-β-D-GlcNAc-(1→, where a critical feature distinguishing O25B from closely related serotypes such as O25A is the presence of O-acetylated rhamnose at the central glycosidic position instead of N-acetyl-fucose[1][2]. The genetic determinants for O25B biosynthesis reside in a specific rfb (O-antigen biosynthesis) locus, which encodes the glycosyltransferases and O-acetyltransferase needed to assemble this antigen[1][2]. The O25B antigen is immunodominant and serves as a major serotype-specific epitope for host immune recognition, as well as a target for vaccine development efforts such as bioconjugate vaccines that present the purified O25B polysaccharide conjugated to a carrier protein to elicit protective antibodies[2]. Its structural uniqueness, restricted to O25B strains, supports its role as a diagnostic marker and a promising target for pathogen-specific vaccine development, especially for combating multidrug-resistant E. coli O25B ST131[1][2].

Other names

E. coli O25B O-antigenO25B polysaccharideO25B antigenO25B LPS (Lipopolysaccharide) O-antigen

Induction of immune responses (vaccine mechanism: antibody-mediated recognition and clearance of O25B-expressing E. coli)[2]