Enterotoxigenic Escherichia coli (ETEC) strains expressing F4 and F18 fimbriae are major causes of neonatal and post‑weaning diarrhea in swine. Although epithelial maturation influences susceptibility in vivo, its impact on ETEC-host interactions remains poorly defined. This study characterizes the genomic diversity, virulence traits, and antibiotic resistance profiles of emerging F18 ETEC isolates using whole-genome sequencing and a differentiated porcine intestinal cell model. Six ETEC genomes: three F18 strains (3EC1, 27EC1, 3247EC), a porcine F4 strain, human ETEC H10407, and the historical F18 strain E. coli Nysø were analyzed by comparative genomics for virulence factors, toxin genes, and antimicrobial resistance (AMR) determinants. Genome sequences were submitted to the Type (Strain) Genome Server (TYGS) for whole genome-based taxonomic classification. Antibiotic susceptibility was phenotypically confirmed by microdilution and disk diffusion assays. Adhesion assays were performed using IPEC‑1, IPEC‑J2, and Caco‑2 cells conditioned to Early (6 days post‑confluence, DPC), Mid (9 DPC), and Late (16 DPC) maturation states. Expression of F18‑binding receptors (FUT1, FUT2) was quantified by RT‑qPCR. IPEC‑1 cells exhibited significantly higher FUT1 and FUT2 expression than IPEC‑J2, corresponding to approximately two‑fold stronger adhesion by most F18 isolates. Strain 3EC1 showed a distinct adhesion peak at 9 DPC, approaching F4 levels, while F4 and H10407 consistently displayed the highest adhesion across all models. Phylogenetic analysis placed 27EC1 and 3247EC in a clade with the F4 strain, whereas 3EC1 clustered with human H10407 and the ancestral E. coli Nysø strain. Comparative genomic analysis revealed substantial heterogeneity among F18 strains in fimbrial loci, flagellin, lipopolysaccharide biosynthesis genes, and AMR genes. Strain 3EC1 uniquely carried stx2e, and 3EC1 and 3247EC were positive for non‑classical EAST1 variants. All F18 isolates encoded hlyE and were β‑hemolytic. Strain 3247EC harbored the largest AMR gene repertoire (28 resistance genes), with all three F18 isolates demonstrating resistance to multiple antibiotic classes. The IPEC‑1/IPEC‑J2 maturation model recapitulates age‑dependent susceptibility to ETEC, driven by FUT1/FUT2 expression levels. The co-occurrence of strong adhesion capacity, stx2e, and extensive antimicrobial resistance in F18 strains underscores the evolution in virulence and the public health relevance of AMR surveillance in swine. This integrated genomic and cell-based platform provides a refined model for studying porcine ETEC pathogenesis and informing the development of targeted intervention strategies.
Liu et al. (Sun,) studied this question.