Search

Background: A Shiga toxin type 2a (Stx2a)-producing enteroaggregative Escherichia coli (EAEC) strain of serotype O104:H4 caused a large outbreak in 2011 in northern Europe. Pathogenic mechanisms for this strain are unclear. We hypothesized that EAEC genes encoded on the pAA virulence plasmid promoted the translocation of Stx2a across the intestinal mucosa., Methods: We investigated the potential contribution of pAA by using mutants of Stx-EAEC strain C227-11, either cured of the pAA plasmid or deleted for individual known pAA-encoded virulence genes (ie, aggR, aggA, and sepA). The resulting mutants were tested for their ability to induce interleukin 8 (IL-8) secretion and translocation of Stx2a across a polarized colonic epithelial (T84 cell) monolayer., Results: We found that deletion of aggR or aggA significantly reduced bacterial adherence and (independently) translocation of Stx2a across the T84-cell monolayer. Moreover, deletion of aggR, aggA, sepA, or the Stx2a-encoding phage from C227-11 resulted in reduced secretion of IL-8 from the infected monolayer., Conclusions: Our data suggest that the AggR-regulated aggregative adherence fimbriae I enhance inflammation and enable the outbreak strain to both adhere to epithelial cells and translocate Stx2a across the intestinal epithelium., (© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Background: Shiga toxin (Stx)-producing Escherichia coli (STEC), especially O157:H7, cause bloody diarrhea, and in 3%-15% of individuals the infection leads to hemolytic uremic syndrome (HUS) or other complications. Use of antibiotics to treat STEC infections is controversial. Here, we describe the use of piglets to evaluate the efficacy and mechanism of action of antibiotics in these infections., Methods: The effects of 2 antibiotics on STEC toxin production and their mechanisms of action were first determined by enzyme-linked immunosorbent assay and subsequently evaluated clinically in the gnotobiotic piglet infection model., Results: In vitro treatment of clinical and isogenic strains with ciprofloxacin increased the production of Stx2 via phage induction but not the production of Stx1. Azithromycin caused no significant increase in toxin production. After treatment with ciprofloxacin, infected piglets had diarrhea and the severe fatal neurological symptoms associated with Stx2 intoxication. Characteristic petechial hemorrhages in the cerebellum were more severe in ciprofloxacin-treated animals than in control animals. In contrast, azithromycin-treated piglets survived the infection and had little or no brain hemorrhaging., Conclusions: The increased in vitro toxin production caused by ciprofloxacin was strongly correlated with death and an increased rate of cerebellar hemorrhage, in contrast to the effect of azithromycin. The piglet is a suitable model for determining the effectiveness and safety of antibiotics available to treat patients.

Shiga toxin (Stx) 2 causes hemolytic-uremic syndrome (HUS), an intractable and often fatal complication of enterohemorrhagic Escherichia coli O157:H7 infection. Here, we show that serum amyloid P component (SAP), a normal human plasma protein, specifically protects mice against the lethal toxicity of Stx2, both when injected into wild-type mice and when expressed transgenically; in the presence of human SAP, there was greatly reduced in vivo localization of Stx2 to the kidneys, suggesting a possible mechanism of protection. In humans, circulating SAP concentrations did not differ between patients with suspected enterohemorrhagic E. coli infection with antibodies to E. coli O157:H7 lipopolysaccharide and those without antibodies or between patients with HUS and those without it. However, the potent protection conferred by human SAP in the mouse model suggests that infusion of supplemental SAP may be a useful novel therapeutic approach to the treatment of this devastating condition.

We tested the combination of phosphodiesterase (PDE) 3 and PDE4 inhibitors as an interventional approach to prevent the development of brain damage after Shiga toxin (Stx)-producing Escherichia coli (STEC) infection, using mice with protein calorie malnutrition. The combination consisted of pentoxifylline and rolipram; the dose of each inhibitor was 7.5 mg/kg. Treatment with this combination, which was administered intraperitoneally twice daily at 12-h intervals, increased serum concentrations of each inhibitor to >2 microg/mL and afforded significant levels of protection when it was continued for 3 days, starting on day 2 (95% survival rate; P<.001) or day 3 (63% survival rate; P<.01) of infection. The treatment reduced plasma levels of Stx2; consequently, immunoreactions of Stx2 were not found in the brain, and survivors did not show neurologic symptoms. Protection was associated with decreased levels of tumor necrosis factor (TNF)- alpha and increased production of interleukin-10 in serum, the brain, and the cecum. Although the combination at doses >2 microg/mL reduced Gb3 content of and Stx2 binding to Caco-2 cells, its ability to suppress production of TNF- alpha seemed to be more important for the decrease in cell-bound Stx2 in intestinal epithelial cells. Therefore, the combination of PDE3 and PDE4 inhibitors might be used as an interventional approach to prevent brain damage caused by STEC infection.

We have previously constructed a recombinant bacterium expressing a modified lipopolysaccharide (LPS) mimicking the Shiga toxin receptor, which binds toxin with high avidity. This involved cloning Neisseria galactosyl transferase genes (lgtC and lgtE) in pK184 in a derivative of Escherichia coli R1 (CWG308). Such constructs have considerable potential for prevention of disease caused by Shiga toxin-producing E. coli (STEC). However, neither the E. coli host strain nor the expression plasmid is suitable for human use, because the former is derived from a clinical isolate and the latter contains a kanamycin-resistance gene. We have constructed, as a prelude to human trials, a nonpathogenic E. coli K-12 C600 derivative with deletions in waaO and waaB, such that it has the same LPS core structure as CWG308. We also deleted the thyA gene from this strain, rendering it thymine dependent. The kanamycin-resistance gene was also deleted from pK184 and was replaced with Salmonella typhimurium thyA. Neisseria lgtCE was then cloned into this plasmid and transformed into C600 Delta waaOB Delta thyA. The plasmid was stably maintained, and the construct produced a modified LPS and neutralized Stx1 and Stx2c. Moreover, mice challenged with an otherwise fatal dose of STEC were completely protected by oral administration of the novel construct.

Shiga toxin (Stx) is a major virulence factor in infection with Stx-producing Escherichia coli (STEC). We developed a series of linear polymers of acrylamide, each with a different density of trisaccharide of globotriaosylceramide (Gb3), which is a receptor for Stx, and identified Gb3 polymers with highly clustered trisaccharides as Stx adsorbents functioning in the gut. The Gb3 polymers specifically bound to both Stx1 and Stx2 with high affinity and markedly inhibited the cytotoxic activities of these toxins. Oral administration of the Gb3 polymers protected mice after administration of a fatal dose of E. coli O157:H7, even when the polymers were administered after the infection had been established. In these mice, the serum level of Stx was markedly reduced and fatal brain damage was substantially suppressed, which suggests that the Gb3 polymers entrap Stx in the gut and prevent its entrance into the circulation. These results indicate that the Gb3 polymers can be used as oral therapeutic agents that function in the gut against STEC infections.

The Shiga toxins Stx1 and Stx2 contribute to the development of enterohemorrhagic O157:H7 Escherichia coli-mediated colitis and hemolytic-uremic syndrome in humans. The Stx2 B subunit, which binds to globotriaosylceramide (GB3) receptors on target cells, was cloned. This involved replacing the Stx2 B subunit leader peptide nucleotide sequences with those from the Stx1 B subunit. The construct was expressed in the TOPP3 E. coli strain. The Stx2 B subunits from this strain assembled into a pentamer and bound to a GB3 receptor analogue. The cloned Stx2 B subunit was not cytotoxic to Vero cells or apoptogenic in Burkitt's lymphoma cells. Although their immune response to the Stx2 B subunit was variable, rabbits that developed Stx2 B subunit-specific antibodies, as determined by immunoblot and in vitro cytotoxicity neutralization assays, survived a challenge with Stx2 holotoxin. This is thought to be the first demonstration of the immunoprophylactic potential of the Stx2 B subunit.