Salmonella enterica serotype Typhimurium Std fimbriae bind terminal alpha(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 (Fucalpha1-2Galbeta1-4GlcNAc) or by pretreatment of cells with alpha1-2 fucosidase. In contrast, pretreatment of Caco-2 cells with neuraminidase or co-incubation with the type 2 disaccharide precursor (Galbeta1-4GlcNAc) did not reduce adherence of Std fimbriated S. Typhimurium. Binding of purified Std fimbriae to Fucalpha1-2Galbeta1-4GlcNAc in a solid phase binding assay was competitively inhibited by Ulex europaeus agglutinin-I (UEA-I), a lectin specific for Fucalpha1-2 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 alpha1-2 fucosylated receptor(s) present in the cecal mucosa.