An Atypical Kappa-Class Chaperone-Usher Fimbriae of a Human Enterotoxigenic Escherichia coli Strain Shows Multi-Host Adherence and Distinct Phylogenetic Feature

The pathogenesis of enterotoxigenic Escherichia coli (ETEC) involves the colonization of hosts by colonization factors (CFs) and the secretion of enterotoxins. CFs, especially chaperone-usher fimbriae, mediate bacterial adhesion to host cells, with extensive genetic diversity observed among isolates. One ETEC strain, O169YN10, possessed a unique plasmid (pEntYN10) encoding three CFs, CS6, and two novel homologs of CS8 and F4 (CS6_O169, CS8_O169, and F4_O169). In this study, F4_O169 was found to play a major role in adhesion to multiple hosts, including human, bovine, and porcine epithelial cells, whereas the other two CSs were less functional. Inhibition assays using antibodies showed that FayG1, one of the two major paralogous adhesins of F4_O169, directly contributes to human cell adhesion. Despite the established function of FayG1, the FayG2 protein was not detected under the in vitro conditions. Comparative genomics revealed that FayG1 and FayG2 share low homology with other E. coli strains isolated from hosts, suggesting sporadic emergence from an unknown origin.