Relative Importance of Heat-Labile Enterotoxin in the Causation of Severe Diarrheal Disease in the Gnotobiotic Piglet Model by a Strain of Enterotoxigenic Escherichia coli That Produces Multiple Enterotoxins

Abstract

Enterotoxigenic Escherichia coli (ETEC) strains that produce multiple enterotoxins are important causes of severe dehydrating diarrhea in human beings and animals, but the relative importance of these enterotoxins in the pathogenesis is poorly understood. Gnotobiotic piglets were used to study the importance of heat-labile enterotoxin (LT) in infection with an ETEC strain that produces multiple enterotoxins. LT ؊ (⌬eltAB) and complemented mutants of an F4؉ LT ؉ STb ؉ EAST1 ؉ ETEC strain were constructed, and the virulence of these strains was compared in gnotobiotic piglets expressing receptors for F4 ؉ fimbria. Sixty percent of the piglets inoculated with the LT ؊ mutant developed severe dehydrating diarrhea and septicemia compared to 100% of those inoculated with the nalidixic acid-resistant (Nal r ) parent and 100% of those inoculated with the complemented mutant strain. Compared to piglets inoculated with the Nal r parent, the mean rate of weight loss (percent per hour) of those inoculated with the LT ؊ mutant was 67% lower (P < 0.05) and that of those inoculated with the complemented strain was 36% higher (P < 0.001). Similarly, piglets inoculated with the LT ؊ mutant had significant reductions in the mean bacterial colony count (CFU per gram) in the ileum; bacterial colonization scores (square millimeters) in the jejunum and ileum; and clinical pathology parameters of dehydration, electrolyte imbalance, and metabolic acidosis (P < 0.05). These results indicate the significance of LT to the development of severe dehydrating diarrhea and postdiarrheal septicemia in ETEC infections of swine and demonstrate that EAST1, LT, and STb may be concurrently expressed by porcine ETEC strains.

Escherichia coli STb toxin induces apoptosis in intestinal epithelial cell lines

“…The lack of diarrhea has been attributed to the lack of presence of fimbriae required for adhesion to the intestinal mucosa (Lortie et al, 1991, Gaastra et al, 1996. The role of STb in swine diarrhea was demonstrated in a study by Berberov et al (2004) who revealed that 60% of piglets inoculated with an ETEC STb + EAST1 + LT -strain developed diarrhea (Berberov et al, 2004). This finding was confirmed by Zhang et al (2006) who observed fluid accumulation in piglets injected with F4 + STb + positive strains.…”

“…The gene coding for EAST-1, astA, is frequently isolated from porcine ETEC strains harbouring the genes for F4 and STa toxin (Choi et al, 2001). The gene astA has also been isolated from healthy subjects, thus the ability of EAST-1 to induce diarrhea mediated by ETEC strains (Ngeleka et al, 2003) and to stimulate loss of electrolytes from intestines (Berberov et al, 2004) currently remains elusive.…”

“…LT has also been associated with severe diarrhea and septicemia in piglets (Berberov et al, 2004). LT toxin is an 84 kDa AB toxin composed of one A subunit and five B subunits linked to each other by a disulfide bonds (Sixma et al, 1991).…”

Presence of Escherichia coli carrying the EAST1 toxin gene in farm animals

“…A total of 34/37 STb-positive strains (either alone or in combination with other toxins) was also positive for EAST1. The importance of this toxin association may have an echo in the study of Berberov et al [4] who recently demonstrated the concurrent expression of LT, STb and EAST1. This study clearly established, using an isogenic strain, that following inactivation of LT toxin production (by deletion), the development of less severe dehydrating diarrhea was observed.…”

“…These E. coli are classified in different pathotypes based on the presence of specific virulence factors [18,4 S. Veilleux, J.D. Dubreuil 41].…”