Abstract
BackgroundEnterotoxigenic 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.Methodology/Principal FindingsIn 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.Conclusion/SignificanceResults 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.
Highlights
Enterotoxigenic Escherichia coli (ETEC) strains are the most common bacterial cause of diarrhea
Strains 8724 and 8725 were derived from transformation of strain 17-2 with labile toxin (LT) plasmid p8607 and stable toxins that include type I (STa) plasmid p8295 to express additional LT and STa, respectively, and were used for comparative studies in EIA ELISAs to determine whether enteroaggregative heat-stable toxin 1 (EAST1) plays a synergistic role to LT or STa toxin in stimulating intracellular cAMP and cGMP in vitro
EAST1 was reported as the only toxin produced by E. coli strain O166 that caused an outbreak of gastroenteritis in Japan in 1996 [44], and EAST1-positive enteroaggregative E. coli (EAEC) strain 17-2 that was suggested to associate with an outbreak in Chile [13]
Summary
Enterotoxigenic Escherichia coli (ETEC) strains are the most common bacterial cause of diarrhea. Enterotoxins produced by ETEC strains associated with diarrhea are heat-labile toxin (LT) and heat-stable toxins (ST) that include type I (STa), type II (STb), and enteroaggregative heat-stable toxin 1 (EAST1) [4,5,6]. 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). Significance of EAST1 in ETEC-associated diarrheal has not been determined, even though EAST1 is highly prevalent among ETEC strains
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