Salmonella enterica serotype Typhimurium Std fimbriae bind terminal α(1,2)fucose residues in the cecal mucosa

The std operon encodes a fimbrial adhesin of Salmonella enterica serotype Typhimurium that is required for attachment to intestinal epithelial cells and for cecal colonization in the mouse. To study the mechanism by which this virulence factor contributes to colonization we characterized its binding specificity. Std-mediated binding to human colonic epithelial (Caco-2) cells could be abrogated by removing N-linked glycans. Adherence of Std fimbriated S. Typhimurium to Caco-2 cells could be blocked by co-incubation with H type 2 oligosaccharide (Fuc alpha 1-2Gal beta 1-4GlcNAc) or by pretreatment of cells with alpha 1-2 fucosidase. In contrast, pretreatment of Caco-2 cells with neuraminidase or co-incubation with the type 2 disaccharide precursor (Gal beta 1-4GlcNAc) did not reduce adherence of Std fimbriated S. Typhimurium. Binding of purified Std fimbriae to Fuc alpha 1-2Gal beta 1-4GlcNAc in a solid phase binding assay was competitively inhibited by Ulex europaeus agglutinin-I (UEA-I), a lectin specific for Fuc alpha 1-2 moieties. Purified Std fimbriae and UEA both bound to a receptor localized in the mucus layer of the murine cecum. These data suggest that the std operon encodes an adhesin that binds an alpha 1-2 fucosylated receptor(s) present in the cecal mucosa.