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Immunochemical characterization of P pili from invasive Escherichia coli
Abstract:
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.
Insights
P pili, crucial for E. coli infections, show significant antigenic diversity despite identical N-terminal sequences. This heterogeneity impacts immune recognition of these bacterial adhesins.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- P pili (fimbriae) are key virulence factors in pyelonephritogenic Escherichia coli.
- These structures mediate bacterial adherence to host cells, including erythrocytes and epithelial cells.
Purpose of the Study:
- To investigate the antigenic diversity of P pili from bacteremic E. coli strains.
- To determine if conserved N-terminal sequences correlate with conserved antigenicity.
Main Methods:
- Purification of P pili from 14 E. coli strains exhibiting mannose-resistant hemagglutination.
- Analysis of pilus protein composition using SDS-PAGE.
- Antigenic characterization via enzyme-linked immunosorbent inhibition assays and immunoblots using rabbit antisera.
- N-terminal protein sequencing of purified P pili.
Main Results:
- Pilus preparations showed molecular weights ranging from 14,000 to 19,500 Da, with one to three distinct protein bands.
- No single pilus band was common across all analyzed strains.
- Enzyme-linked immunosorbent inhibition assays and immunoblots revealed significant antigenic heterogeneity among P pili.
- Despite identical N-terminal amino acid sequences in four P pili, their overall antigenicity differed substantially.
Conclusions:
- P pili from E. coli exhibit considerable antigenic diversity, even when sharing identical N-terminal sequences.
- The receptor-binding domains, likely conserved, appear to be 'immunorecessive', meaning they do not elicit strong or distinguishing immune responses.
- This antigenic variation has implications for vaccine development and understanding host-pathogen interactions.