Genomic analysis and adhesion characteristics of enterotoxigenic Escherichia coli F4 and F18 strains on porcine intestinal epithelial cell lines

Background: Enterotoxigenic Escherichia coli (ETEC) strains are the primary perpetrators of colibacillosis in piglets, resulting in mortality and agribusiness economic woes. ETEC expressing fimbrial antigens, F4 and F18, are the predominant contributors to colibacillosis. F4 is most prevalent in neonatal diarrhea. F18 is more common in post-weaning colibacillosis. Intestinal epithelial interaction and colonization are crucial steps toward colibacillosis. Understanding the genotypic virulence properties and their interaction with swine intestinal cells can help develop mitigation strategies.

Methods: We investigated 3 colibacillosis-causing F18 strains (3EC1, 27EC1, and 3247EC) isolated from swine in Iowa and Maryland and a single human ETEC isolate (O78:H11). We compared their whole genome sequence (WGS), virulence gene profiles, and adhesion characteristics to swine intestinal IPEC-1 and IPEC-J2 cell lines.

Results: All F18 isolates were β-hemolytic and positive for the fimbrial gene, fedA. F4 was positive for k88c analyzed by PCR. WGS of 3 F18 strains and F4 revealed sequence variation associated with flagellin, fimbriae, and lipopolysaccharide (LPS) without any differences in toxin gene profiles (EAST1, OrtT, RatA, etc.). No F18 strains possessed genes that encode heat-labile (LT), heat-stable (STa, STb), or Shiga toxins (Stx1, Stx2, or Stx2e). Adhesion of F18 to IPEC-1 and IPEC-J2 cell lines showed variable results after 30 min without statistical significance. Likewise, the F4 strain showed similar adhesion to both cell lines. The lactate dehydrogenase (LDH)-based cytotoxicity assay and microscopic examination showed no cell damage during the 30-min ETEC exposure.

Significance: Despite a significant genotypic difference between F18 and F4 strains, all showed strong interaction with pig intestinal epithelial cell lines, IPEC-1 and IPEC-J2. The results offer insights into developing more effective mitigation measures using these cell models.

Key Words: ETEC, genomics, swine, adhesion.