Immunochemical characterization of P pili from invasive Escherichia coli

P pili (or fimbriae) are present on most pyelonephritogenic Escherichia coli strains, and they mediate binding to erythrocytes and epithelial cells. To determine the antigenic diversity of P pili, we purified the pili from 14 bacteremic E. coli strains which caused mannose-resistant hemagglutination. Pilus preparations consisted of one to three bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ranged in molecular weight from 14,000 to 19,500. There was no single band common to all the strains. An enzyme-linked immunosorbent inhibition assay detected 20 ng of pilus antigen. When four different rabbit antisera were used, only two or fewer heterologous strains could inhibit the enzyme-linked immunosorbent assay. Immunoblots yielded the same results. Protein sequences of four P pili had identical N termini. These results show that despite having identical amino-terminal sequences, P pili are antigenically heterogeneous. The receptor-binding domains which are likely to be identical in all strains must be immunorecessive.