Escherichia coli carrying the F18 fimbriae colonize the small intestine of pigs and cause postweaning
diarrhea and
edema disease. There are 2 closely related antigenic variants of F18, F18ab, and F18ac. While F18ab-positive strains are known to be associated with
edema disease, E. coli-carrying F18ac are known to cause
diarrhea. One hundred ninety-eight E. coli isolates obtained from cases of
diarrhea and
edema disease in pigs isolated from feces or intestine were screened for the presence of the
fedA gene encoding for F18 fimbriae. To distinguish between F18ab and F18ac, the
fedA gene was sequenced in 69 F18-positive isolates/strains. The translated
protein sequences of the
fedA gene in the 2 variants differ; F18ac
protein carries
proline at
amino acid residue 121, which is substituted or missing in F18ab. The F18ab- and F18ac-positive E. coli strains were compared for the presence of virulence attributes, serotypes of the isolates, and relatedness between the strains. Contrary to earlier reports that E. coli F18ab-positive strains mostly express
Shiga toxin and F18ac-positive strains generally express
enterotoxins, the current report shows conclusively for the first time that both variant types may carry genes for
Shiga toxins and/or
enterotoxins.
Monoclonal antibodies produced against F18ab or F18ac fimbriae could not distinguish the strains carrying the 2 variants. Therefore, it was concluded that either of the 2 F18 variants, F18ab or F18ac, may be involved in causing postweaning
diarrhea or
edema disease in pigs.