DNA Sequences of Three PapA Genes from Uropathogenic Escherichia Coli Strains: Evidence of Structural and Serological Conservation

Pyelonephritis-associated pili (Pap) are important in the pathogenesis of ascending, unobstructive Escherichia coli-caused renal infections because these surface bacterial organelles mediate digalactoside-specific binding to host uroepithelial cells. Pap are composed of many different polypeptides, of which only the tip proteins mediate specific binding. The PapA moiety polymerizes to form the bulk of the pilus structure and has been employed in vaccines despite its lack of Gal alpha(1-4)Gal receptor specificity. Animal recipients of PapA pilus-based vaccines are protected against experimental pyelonephritis caused by homologous and heterologous Gal-Gal-binding uropathogenic E. coli strains. Specific PapA immunoglobulin G antibodies in urine are correlated with protection in these infection models. The nucleotide sequences of the gene encoding PapA were determined for three E. coli clones expressing F7(1), F7(2), and F9 pili and were compared with corresponding sequences for other F serotypes. Specific rabbit antisera were employed in enzyme-linked immunosorbent assays to study the cross-reactivity between Gal-Gal pili purified from recombinant strains expressing F7(1), F7(2), F9, or F13 pili and among 60 Gal-Gal-binding wild-type strains. We present data which corroborate the concept that papA genes are highly homologous and encode proteins which exhibit greater than 70% homology among pili of different serotypes. The differences primarily occur in the cysteine-cysteine loop and variable regions and constitute the basis for serological diversity of these pili. Although there are differences in primary structures among these pili, antisera raised against pili of one serotype cross-reacted frequently with many other Gal-Gal pili of different serotypes. Furthermore, antisera raised against pili of the F13 serotype cross-reacted strongly or moderately with 52 (86%) of 60 wild-type Gal-Gal-binding E. coli strains. These data suggest that there are common immunogenic domains among these proteins. These additional data further support the hypothesis that broadly cross-protective PapA pilus vaccines for the immunoprophylaxis of pyelonephritis might be developed.