Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/1997
Publication Date: N/A
Interpretive Summary: Bacteria called Escherichia coli (E. coli) are the most frequently identified causes of diarrhea in newborn and weaned pigs. E. coli causes diarrhea because it adheres to cells or the small intestine and produces toxins. Several different toxins produced by E. coli are important in causing diarrhea. We studied one of these toxins, called "heat-stable enterotoxin b" or STb to see if that toxin is important for causing diarrhea. We did this by comparing two nearly identical E. coli strains. The only difference between these strains was that one made only STb toxin and the other did not make any toxin. We found that both these E. coli strains could adhere and grow in the small intestine. The strain that produced the STb toxin did not cause more severe diarrhea than did the strain without STb. This work shows that the STb toxin produced by some E. coli is not sufficient for causing severe diarrhea in newborn pigs. Knowing the E. coli characteristics that are needed to cause diarrhea and those that are not needed is information that can be used by diagnostic laboratories to accurately identify important E. coli. This information is also an important first step for designing effective vaccines and for identifying other ways for producers and veterinarians to prevent diarrhea in newborn pigs caused by E. coli.
Technical Abstract: The role of the 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 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.