Expression of heat-stable enterotoxin STb by adherent Escherichia coli is not sufficient to cause severe diarrhea in neonatal pigs

Abstract

The role of Escherichia coli heat-stable enterotoxin B (STb) in neonatal porcine diarrhea caused by enterotoxigenic E. coli was examined by comparing adherent isogenic strains with or without STb. The cloned STb gene (in the plasmid pRAS1) was electroporated into a nonenterotoxigenic strain (226M) which expresses the F41 adhesin. Strain 226M pRAS1 adhered and expressed STb in vivo, causing fluid secretion in ligated ileal loops in neonatal pigs. Although strain 226M pRAS1 caused very mild diarrhea in some orally inoculated neonatal pigs, the weight loss in these pigs was similar to that caused by the parental strain without STb. We conclude that STb does not significantly contribute to diarrhea caused by enterotoxigenic E. coli in neonatal pigs.

FIG. 1

Mean fluid accumulation per cm (± standard error of the mean) and bacterial adherence for the indicated strains in ligated ileal loops made in neonatal pigs. Fluid accumulation is expressed as final loop volume per centimeter (Vf/cm). Loop adherence is expressed as number of loops with adherent bacteria per number of loops examined. The number of loops for each strain is the same for fluid accumulation measurements and adherence determinations.