Structure and gene cluster of the O antigen of Escherichia coli F17, a candidate for a new O-serogroup.

The research article outlines a study on the structure and genetics of the O antigen of a specific strain of Escherichia coli (E. coli F17), isolated from horse feces, suggesting its potential as a new O-serogroup.

Research Methodology and Findings

• The researchers isolated the lipopolysaccharide (LPS) from E. coli F17 bacterial cells using a process known as phenol-water extraction.
• This LPS was then split or ‘cleaved’ through a process of mild acid hydrolysis, which resulted in the formation of the O polysaccharide (O antigen).
• The structure of the O polysaccharide was determined using sugar analysis and selective solvolysis with CFCOH, combined with one- and two-dimensional H and C NMR spectroscopy.
• They found that the O polysaccharide has a unique branched pentasaccharide repeat (O-unit) structure, containing one residue each of d-galactose, d-mannose, l-rhamnose, d-glucuronic acid, and N-acetyl-d-glucosamine; approximately 2/3 units have a side-chain glucose residue.

O-Antigen Gene Cluster

• Besides the O-polysaccharide structure, the researchers also sequenced the O-antigen gene cluster of E. coli F17. They found it to be 99% identical to that of E. coli 102,755 which is assigned to a novel OgN8 genotype.
• The team annotated the genes in the cluster considering the F17 O-polysaccharide structure. This process involved identifying the function and position of each gene.
• The close similarity confirmed that E. coli F17 and E. coli strains of the OgN8 genotype could potentially be classified as a new E. coli O-serogroup.

Potential Effects and Implications

• The O antigen of this new type was found to effectively shield the outer membrane surface of the bacteria, thereby protecting it from interaction with bacteriophages, a type of virus that infects bacteria.
• This unique O-antigen structure and its protective role could provide an avenue for further research into disease prevention measures or treatments targeting E. coli infections.