Enteroaggregative Escherichia coli heat-stable enterotoxin 1 represents another subfamily of E. coli heat-stable toxin.

Abstract

Enteroaggregative Escherichia coi (EAggEC) are associated with persistent diarrhea in young children. Some of these organisms produce a low-molecular-weight, heat-stable, plasmid-encoded enterotoxin that has been named EAggEC heat-table enterotoxin 1 (EAST1). We have cloned a 4.4-kb DNA fragment from the virulence plasmid of prototype EAggEC strain 17-2, which expresses enterotoxic activity as measured by electrogenic response in Ussing chambers mounted with rabbit ileal tissue. DNA-sequence analysis ofthis fragment identified an open reading frame (ORF) encoding a cysteine-rich polypeptide of 38 amino acids (Mr, 4100). Insertional and deletional mutations in this ORF resulted in loss of enterotoxic activity. The ORF was cloned into a T7 expression vector, and postinduction culture filtrates exhibited enterotoxic activity and increased ileal tissue cGMP levels. A synthetic peptide consisting of predicted amino acid residues 8-29 also showed enterotoxic activity. These data indicate that this ORF, named astA (EAggEC heat-table enterotoxin), represents the EASTI structural gene. EAST1 shows significant homology with the enterotoxic domain of heat-stable enterotoxin a (STa) of enterotoxigenic E. coil and with guanylin, a mammalian analog of STa. Unlike STa, which requires six cysteines and three disulfide linkages for ful biological activity, both EAST1 and guanylin contain four cysteine residues. Based on the cGMP data and the sequence homology to STa and guanylin, it is predicted that EAST1 stimulates the particulate form ofguanylate cyclase through the same receptorbinding region as STa and guanylin.

Prevalence of the Enteroaggregative Escherichia Coli Heat-Stable Enterotoxin 1 Gene and Its Relationship with Fimbrial and Enterotoxin Genes in E. Coli Isolated from Diarrheic Piglets

“…Both EAST1 and STa activate guanylate cyclase. 9 However, EAST1 is detected in the rabbit and STa is detected in suckling mice. 2,8 There are notable differences between these 2 moieties.…”

“…The classical method for detection of EAST1 is the rabbit ileal mucosa assay, which employs the Ussing chamber, 8,9 but it is expensive and time consuming and requires euthanasia of animals. The PCR test is sensitive and can be completed rapidly, giving results such as the identification of the EAST1 gene within 1 working day.…”

Escherichia coli virulence factors

“…5 kDa (Dubreuil, 2008) and EAST1 is a 38 amino-acid toxin of ca. 4 kDa (Savarino et al, 1993). Because of their low molecular weight, no oligopeptide toxin is a good immunogen.…”

“…E. coli even produces different oligopeptide toxins, like the heat-stable enterotoxins of enterotoxigenic strains (STaP, STaH and STb) and the heat-stable enterotoxin of enteroaggregative strains (EAST1) (Smith and Halls, 1967;Burgess et al, 1978;Moseley et al, 1983;Savarino et al, 1993). STaP and STaH are 18 and 19 amino-acid peptides respectively of a molecular weight of less than 2 kDa (Moseley et al, 1983), whereas STb is a 48 amino-acid peptide of ca.…”

Les récepteurs des entérotoxines bactériennes

“…La toxine EAST1 des E. coli entéroaggrégatives est très apparentée à la guanyline. Le domaine d'attachement de la guanyline et de l'entérotoxine STa avec le récepteur protéique GC-C serait identique à celui de EAST1 [130,164]. La toxine thermostable de Yersinia enterocolitica, souvent impliquée dans les gastroentérites de l'enfant, rappelle également STa par sa structure similaire, son récepteur et son mode d'action communs [124,145].…”