Veterinary diagnostic laboratories frequently recover Escherichia coli (E. coli) strains from sick piglets that do not appear to contain either the F4 or F18 fimbriae, but do carry the genes for enterotoxins and/or Shiga toxin. Therefore, it is not known whether these E. coli strains cause disease in weaned pigs.

Researchers at Iowa State University’s Department of Veterinary Microbiology examined the adherence of 29 fimbriae-negative E. coli strains to human and pig skin cells. The majority of the strains adhered to the porcine cell line, but the pattern of adherence was different from the F-18-positive strains.

Two of the fimbriae-negative E. coli strains were injected into 3-week-old piglets. Neither of these isolates reproduced clinical signs of postweaning diarrhea or gut edema disease, even though both strains carried the edema disease toxin on their genome.

Overall, these data suggest that fimbriae-negative E. coli strains are not pathogenic for weaned pigs even if they carry the toxins normally associated with postweaning diarrhea or gut edema disease.

As a result, veterinarians and producers may wish to pursue other reasons or treatment to help determine the cause of the postweaning diarrhea.

Funding for this research project was provided by the National Pork Board.

Researchers: Nancy Cornick and Dianna Jordan, Iowa State University. For more information, contact Cornick by e-mail at