Antibiotic treatment of children with E. coli O157:H7 infection increases the risk of the hemolytic-uremic syndrome.

The mechanisms used by Shiga toxin (Stx)-producing Escherichia coli to adhere to epithelial cells are incompletely understood. Two cosmids from an E. coli O157:H7 DNA library contain an adherence-conferring chromosomal gene encoding a protein similar to iron-regulated gene A (IrgA) of Vibrio cholerae (M. B. Goldberg, S. A. Boyko, J. R. Butterton, J. A. Stoebner, S. M. Payne, and S. B. Calderwood, Mol. Microbiol. 6:2407-2418, 1992). We have termed the product of this gene the IrgA homologue adhesin (Iha), which is encoded by iha. Iha is 67 kDa in E. coli O157:H7 and 78 kDa in laboratory E. coli and is structurally unlike other known adhesins. DNA adjacent to iha contains tellurite resistance loci and is conserved in structure in distantly related pathogenic E. coli, but it is absent from nontoxigenic E. coli O55:H7, sorbitol-fermenting Stx-producing E. coli O157:H؊, and laboratory E. coli. We have termed this region the tellurite resistance-and adherence-conferring island. We conclude that Iha is a novel bacterial adherence-conferring protein and is contained within an E. coli chromosomal island of conserved structure. Pathogenic E. coli O157:H7 has only recently acquired this island.Escherichia coli O157:H7 and other Shiga toxin (Stx)-producing E. coli (STEC) strains cause diarrhea, hemorrhagic colitis, and the hemolytic uremic syndrome. The mechanisms underlying the adherence of STEC to epithelial cells are only partly understood (35). The ability to adhere to epithelial cells is an important virulence trait, because adherence presumably enables enteric pathogens to deliver toxins efficiently to host organs, overcome peristaltic clearance, and gain access to hostderived nutrients.Intimin is the best-characterized E. coli O157:H7 adherence molecule. Encoded by eae, intimin mediates the attaching and effacing lesion caused by enteropathogenic E. coli (EPEC) and many STEC serotypes (21) and is an important component of pathogenicity. However, cloned eae from EPEC and STEC do not confer the adherent phenotype upon laboratory E. coli (18,25,28). Moreover, though the cloned EPEC locus of enterocyte effacement, which includes eae, does confer the adherence phenotype on E. coli K-12 (27), the cloned E. coli O157:H7 locus of enterocyte effacement does not (12).We describe an E. coli O157:H7 gene that renders laboratory E. coli adherent to epithelial cells and explore evolutionary aspects of its acquisition.(These data were presented in part at the 3rd International Symposium and Workshop on Shiga Toxin-Producing Escherichia coli Infections, Baltimore, Md., 22 to 26 June 1997.) MATERIALS AND METHODSBacteria. The bacteria analyzed in this study are described in Table 1. The bacteria were inoculated directly from frozen stock (in Luria-Bertani [LB] broth-15% glycerol, maintained at Ϫ70°C) into LB broth (26). The cultures were grown overnight under standardized conditions (37°C; 14 to 16 h; stationary cultures) for adherence assays and protein preparations. The bacteria were grown in a shaking incubator (37°C; 14 to 24 h) f...

Hemolytic uremic syndrome (HUS) usually occurs after infection with Shiga toxin-producing bacteria. Thrombotic thrombocytopenic purpura, a disorder with similar clinical manifestations, is associated with deficient activity of a circulating metalloprotease that cleaves von Willebrand factor at the Tyr842-Met843 peptide bond in a shear stress-dependent manner. We analyzed von Willebrand factor-cleaving metalloprotease activity and the status of von Willebrand factor in 16 children who developed HUS after Escherichia coli O157:H7 infection and in 29 infected children who did not develop this complication. Von Willebrand factor-cleaving metalloprotease activity was normal in all subjects, but von Willebrand factor size was decreased in the plasma of each of 16 patients with HUS. The decrease in circulating von Willebrand factor size correlated with the severity of thrombocytopenia and was proportional to an increase in von Willebrand factor proteolytic fragments in plasma. Immunohistochemical studies of the kidneys in four additional patients who died of HUS demonstrated glomerular thrombi in three patients, and arterial and arteriolar thrombi in one patient. The glomerular thrombi contained fibrin but little or no von Willebrand factor. A decrease in large von Willebrand factor multimers, presumably caused by enhanced proteolysis from abnormal shear stress in the microcirculation, is common in HUS. HUS, characterized by acute renal failure, hemolysis with schistocytes on blood smears, and thrombocytopenia, is accompanied by thrombotic microangiopathy of the kidneys and of other organs (1). The syndrome covers a diverse spectrum of microangiopathic disorders (2-4), but most cases occur after infection with Shiga toxin-producing bacteria, such as Escherichia coli O157:H7 (5) or Shigella dysenteriae serotype 1 (6).TTP, a disorder with some clinical, laboratory, and histopathologic similarities to HUS, has been associated with abnormal homeostasis of von Willebrand factor, a protein that is secreted from endothelial cells as a disulfide-linked polymer of a polypeptide with 2050 amino acid residues. Circulating von Willebrand factor is normally cleaved between Tyr842 and Met843 (7) in a shear stress-dependent manner (8) by a plasma metalloprotease (9, 10), generating a series of multimers. Without this metalloprotease activity, von Willebrand factor, when unfolded by shear stress (11), has increased platelet-aggregating activity (12). It is postulated that this increased activity facilitates the formation of arteriolar and capillary platelet thrombi in TTP. Indeed, acquired TTP has been associated with deficient von Willebrand factor-cleaving metalloprotease activity caused by inhibitory antibodies (12, 13).