Structural and Genetic Identification of the O-Antigen from an Escherichia coli Isolate, SD2019180, Representing a Novel Serogroup.

The O-antigen is one of the outermost surface components of Gram-negative bacteria. Its large structural variation provides the molecular basis for bacterial serological diversity. Here, we established the structure of the O-antigen from an strain, SD2019180, which appeared to be completely different from the known serogroups. The O-antigen tetrasaccharide biological repeating unit was identified as → 2)-[β-d-GlcA-(1 → 4)]-[α-d-Gal-(1 → 3)]-α-l-Fuc-(1 → 3)-α-d-GlcNAc-(1 →. Furthermore, we analyzed the O-antigen gene cluster of SD2019180 and confirmed its role in O-antigen synthesis by using deletion and complementation experiments. Our findings indicate that SD2019180 is a novel serogroup of .