Novel molecular variants of allele I of the Escherichia coli P fimbrial adhesin gene papG

P fimbriae of extraintestinal pathogenic Escherichia coli mediate digalacto side-specific adherence via the tip adhesin molecule PapG, which occurs in three known variants (I to III), which are encoded by the corresponding thr ee alleles of papG. In the present study, newly discovered variants of papG allele I and the respective wild-type source strains were characterized. O ne of the new papG allele I variants conferred a unique agglutination pheno type that combined the phenotypes associated with papG alleles I, II, and I II. Comparative hydrophilicity analysis of predicted PapG peptides revealed regions that might explain the observed phenotypic similarities and differ ences between the PapG variants. The new papG allele I variants occurred ei ther as the sole papG allele or together with both papG alleles II and III, rather than with only papG allele III, as in archetypal strains J96 and CP 9. They also occurred in the absence of the usual F13 papA allele. One of t he new papG allele I variants occurred in a serogroup O6 strain that, accor ding to random amplified polymorphic DNA analysis, was phylogenetically dis tant from the "J96-like" clonal group off. coli O4:H5, which includes all p reviously identified examples of papG allele I. Cluster analysis of nucleot ide and predicted peptide sequences suggested that papG allele I represents the earliest evolutionary branch from a common papG ancestor. These result s demonstrate unexpected diversity within papG allele I and, together with previous findings, suggest that the J96-like clonal group of E. coli O4:H5 may represent the original source of papG within the species.