Binding specificity of Salmonella plasmid-encoded fimbriae assessed by glycomics

The Salmonella enterica serotype Typhimurium (S. Typhimurium) genome encodes 12 intestinal colonization factors of the chaperone/usher fimbrial assembly class; however, the binding specificity is known for only one of these adhesins, known as type 1 fimbriae. Here we explored the utility of glycomics to determine the carbohydrate binding specificity of plasmid-encoded fimbriae from S. Typhimurium. A cosmid carrying the pef operon was introduced into Escherichia coli and expression of fimbrial filaments composed of PefA confirmed by flow cytometry and immune-electron microscopy. Plasmid-encoded fimbriae were purified from the surface of E. coli, and the resulting preparation was shown to contain PefA as the sole major protein component. The binding of purified plasmid-encoded fimbriae to a glycanarray suggested that this adhesin specifically binds the trisaccharide Galbeta1-4(Fucalpha1-3)GlcNAc, also known as the Lewis X (Le(x)) blood group antigen. Results from the glycanarray were validated by enzyme-linked immunosorbent assay (ELISA) in which plasmid-encoded fimbriae bound Le(x)-coated wells in a concentration-dependent manner. The binding of plasmid-encoded fimbriae to Le(x)-coated wells could be inhibited by co-incubation with soluble Le(x) antigen. Our results establish glycomic analysis as a promising new approach for determining the carbohydrate binding specificity of bacterial adhesins.