The level of mRNA encoding the transferrin receptor (TfR) is regulated by iron, and this regulation is me-

The hemolytic uremic syndrome (HUS) whose main causative agent is enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a disease that mainly affects children under 5 years of age. Argentina is the country with the highest incidence of HUS in the world. Cattle are a major reservoir and source of infection with E. coli O157:H7. To date, the epidemiological factors that contribute to its prevalence are poorly understood. Single nucleotide polymorphism (SNP) typing has helped to define nine E. coli O157:H7 clades and the clade 8 strains were associated with most of the cases of severe disease. In this study, eight randomly selected isolates of EHEC O157:H7 from cattle in Argentina were studied as well as two human isolates. Four of them were classified as clade 8 through the screening for 23 SNPs; the two human isolates grouped in this clade as well, while two strains were closely related to strains representing clade 6. To assess the pathogenicity of these strains, we assayed correlates of virulence. Shiga toxin production was determined by an ELISA kit. Four strains were high producers and one of these strains that belonged to a novel genotype showed high verocytotoxic activity in cultured cells. Also, these clade 8 and 6 strains showed high RBC lysis and adherence to epithelial cells. One of the clade 6 strains showed stronger inhibition of normal water absorption than E. coli O157:H7 EDL933 in human colonic explants. In addition, two of the strains showing high levels of Stx2 production and RBC lysis activity were associated with lethality and uremia in a mouse model. Consequently, circulation of such strains in cattle may partially contribute to the high incidence of HUS in Argentina.

Postdiarrhea hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in children in Argentina. It is well established that Shiga toxin type 2 (Stx2) causes direct damage to glomerular endothelial cells and tubular epithelial cells, leading to a reduction in the water handling capacity of the kidney. In this study, we demonstrate that Stx2 and its B subunit (Stx2B) were able to inhibit water absorption across human renal tubular epithelial cell (HRTEC) monolayers without altering the short circuit current and the (3)H-mannitol permeability. Quantitative evaluation of (14)C-inulin transport across HRTEC monolayers showed a similar transport rate both before and after HRTEC treatment with Stx2 that confirmed the integrity of the paracellular pathway. Furthermore, Stx2 produced significant protein synthesis inhibition of HRTEC at concentrations as low as 0.001 ng/ml and 1 h of incubation, whereas Stx2B did not modify it at concentrations as high as 10,000 ng/ml and 6 h of incubation. Our findings suggest that whereas the action of Stx2 appears to be caused mainly by the inhibition of protein synthesis mediated by the A subunit, the binding of Stx2B subunit to the Gb3 receptor may affect the membrane mechanisms related to water absorption. We speculate that inhibition of water absorption may occur in proximal tubular cells in vivo in response to Stx2 and may contribute to the early event of HUS pathogenesis.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of intestinal disease and hemolytic uremic syndrome, a serious systemic complication that particularly affects children. Cattle are primary reservoirs for EHEC O157:H7 and the main source of infection for humans. Vaccination of cattle with different combinations of bacterial virulence factors has shown efficacy in decreasing EHEC O157:H7 shedding. It is, therefore, important to demonstrate whether vaccination of pregnant cows with EHEC O157:H7 induces high titers of transferable antibodies to avoid early colonization of calves by the bacteria. In this study we evaluated the ability of EspA, EspB, the C-terminal fragment of 280 amino acids of γ-intimin (γ-intimin C₂₈₀) and inactivated Shiga toxin (Stx) 2 proteins to induce specific antibodies in colostrum and their passive transference to colostrum-fed calves. Friesian pregnant cows immunized by the intramuscular route mounted significantly high serum and colostrum IgG responses against EspB and γ-intimin C₂₈₀ that were efficiently transferred to their calves. Antibodies to EspB and γ-intimin C₂₈₀ were detected in milk samples of vaccinated cows at d 40 postparturition. Significant Stx2-neutralizing titers were also observed in colostrum from Stx2-vaccinated cows and sera from colostrum-fed calves. The results presented showed that bovine colostrum with increased levels of antibodies against EHEC O157:H7 may be obtained by systemic immunization of pregnant cows, and that these specific antibodies are efficiently transferred to newborn calves by feeding colostrum. Hyperimmune colostrum and milk may be an alternative to protect calves from early colonization by EHEC O157:H7 and a possible key source of antibodies to block colonization and toxic activity of this bacterium.