von Willebrand factor and von Willebrand factor-cleaving metalloprotease activity in Escherichia coli O157:H7-associated hemolytic uremic syndrome

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.

The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections

BACKGROUND

Children with gastrointestinal infections caused by Escherichia coli O157:H7 are at risk for the hemolytic-uremic syndrome. Whether antibiotics alter this risk is unknown.

METHODS

We conducted a prospective cohort study of 71 children younger than 10 years of age who had diarrhea caused by E. coli O157:H7 to assess whether antibiotic treatment in these children affects the risk of the hemolytic-uremic syndrome and to assess the influence of confounding factors on this outcome. Estimates of relative risks were adjusted for possible confounding effects with the use of logistic-regression analysis.

RESULTS

Among the 71 children, 9 (13 percent) received antibiotics and the hemolytic-uremic syndrome developed in 10 (14 percent). Five of these 10 children had received antibiotics. Factors significantly associated with the hemolytic-uremic syndrome were a higher initial white-cell count (relative risk, 1.3; 95 percent confidence interval, 1.1 to 1.5), evaluation with stool culture soon after the onset of illness (relative risk, 0.3; 95 percent confidence interval, 0.2 to 0.8), and treatment with antibiotics (relative risk, 14.3; 95 percent confidence interval, 2.9 to 70.7). The clinical and laboratory characteristics of the 9 children who received antibiotics and the 62 who did not receive antibiotics were similar. In a multivariate analysis that was adjusted for the initial white-cell count and the day of illness on which stool was obtained for culture, antibiotic administration remained a risk factor for the development of the hemolytic uremic syndrome (relative risk, 17.3; 95 percent confidence interval, 2.2 to 137).

CONCLUSIONS

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

Iha: a novel Escherichia coli O157:H7 adherence-conferring molecule encoded on a recently acquired chromosomal island of conserved structure

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.