Escherichia coli expressing EAST1 toxin did not cause an increase of cAMP or cGMP levels in cells, and no diarrhea in 5-day old gnotobiotic pigs.
BACKGROUND
Enterotoxigenic Escherichia coli (ETEC) strains are the leading bacterial cause of diarrhea to humans and farm animals. These ETEC strains produce heat-labile toxin (LT) and/or heat-stable toxins that include type I (STa), type II (STb), and enteroaggregative heat-stable toxin 1 (EAST1). LT, STa, and STb (in pigs) are proven the virulence determinants in ETEC diarrhea. However, significance of EAST1 in ETEC-associated diarrheal has not been determined, even though EAST1 is highly prevalent among ETEC strains.


RESULTS
In this study, we constructed E. coli strains to express EAST1 toxin as the only toxin and studied them in cell lines and five-day old gnotobiotic piglets to determine significance of EAST1 toxin. Data from in vitro studies indicated that EAST1 did not stimulate an increase of intracellular cyclic AMP or GMP levels in T-84 cells or porcine cell line IPEC-J2, nor did it enhance LT or STa toxin of ETEC strains in stimulation of cAMP or cGMP in T-84 cells. In addition, 5-day old gnotobiotic pigs challenged with E. coli strains expressing EAST1 as the only toxin did not developed diarrhea or signs of clinical disease during 72 h post-inoculation.


CONCLUSIONS
Results from this study indicated that EAST1 alone is not sufficient to cause diarrhea in five-day old gnotobiotic pigs, and suggest that EAST1 likely is not a virulence determinant in ETEC-associated diarrhea.
Veterinary and Biomedical Sciences Department/The Center for Infectious Disease Research and Vaccinology, South Dakota State University, Brookings, South Dakota, United States of America.
Xiaosai
X
Ruan
Scott S
SS
Crupper
Bruce D
BD
Schultz
Donald C
DC
Robertson
Weiping
W
Zhang
D000818:Animals; D001427:Bacterial Toxins / Q000096:biosynthesis*; D002460:Cell Line; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D003967:Diarrhea / Q000382:microbiology*; D054307:Enterotoxigenic Escherichia coli / Q000378:metabolism*; D004768:Enterotoxins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D029968:Escherichia coli Proteins; D010957:Plasmids / Q000378:metabolism; D015995:Prevalence; D013552:Swine; D013997:Time Factors; D014774:Virulence
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C034151:heat stable toxin (E coli); D000242:Cyclic AMP; D006152:Cyclic GMP