Binding characteristics of Escherichia coli adhesins in human urinary bladder

We studied domains in the human bladder that acted as receptors for Escherichia coli P, S, type 1, type 1C, and O75X fimbriae or adhesin and domains in the human kidneys that were receptors for E. coli type 1C fimbriae. Binding sites in frozen tissue sections were localized by direct staining with fluorochrome-labeled recombinant strains and by indirect immunofluorescence with the purified adhesins. In the bladder, the P and S fimbriae showed closely similar binding to the epithelial and muscular layers, and the S fimbriae also bound to the connective tissue elements. Type 1 fimbriae bound to vascular walls and to muscle cells, whereas the O75X adhesin bound avidly to connective tissue elements and to some extent to epithelial and muscle cells of the bladder. The type 1C fimbriae bound to distal tubules and collecting ducts of the kidney and to vascular endothelial cells in both the kidney and bladder. The binding of all adhesin types was inhibited by specific receptor analogs or Fab fragments. The results reveal a possible mechanism by which the type 1C fimbriae may help invasion of E. coli in the kidneys but do not support a pathogenetic role for type 1 fimbriae. Similar tissue specificity of P and S fimbriae in the human urinary tract indicates that the presence of binding sites on uroepithelia does not fully explain the virulence properties of P fimbriae in human urinary tract infections.