The pathogenesis of Shigella diarrhea. V. Relationship of shiga enterotoxin, neurotoxin, and cytotoxin

Shiga Toxin-Associated Hemolytic Uremic Syndrome: Specificities of Adult Patients and Implications for Critical Care Management

Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome (STEC-HUS) is a form of thrombotic microangiopathy secondary to an infection by an enterohemorrhagic E. coli. Historically considered a pediatric disease, its presentation has been described as typical, with bloody diarrhea at the forefront. However, in adults, the clinical presentation is more diverse and makes the early diagnosis hazardous. In this review, we review the epidemiology, most important outbreaks, physiopathology, clinical presentation and prognosis of STEC-HUS, focusing on the differential features between pediatric and adult disease. We show that the clinical presentation of STEC-HUS in adults is far from typical and marked by the prevalence of neurological symptoms and a poorer prognosis. Of note, we highlight knowledge gaps and the need for studies dedicated to adult patients. The differences between pediatric and adult patients have implications for the treatment of this disease, which remains a public health threat and lack a specific treatment.

Effect of Shiga toxin and Shiga-like toxins on eukaryotic cells

Shigella dysenteriae and Shiga-toxin-producing Escherichia coli (STEC) elaborate the AB holotoxins, Shiga or Shiga-like toxins (Stx). Stx play a major role in the pathogenesis of haemorrhagic colitis and haemolytic uremic syndrome. This review provides an overview of the mechanisms of action of Stx and a model of the pathogenesis of Stx-induced disease.

Shigella-induced encephalopathy in an adult

A 71-year-old woman presented with altered level of consciousness following episodes of diarrhea and abdominal pain. Shigella sonnei was later cultured from her stool. Although neurological complications, primarily seizures, have been reported sequelae in children afflicted shigellosis, there are only rare cases of encephalopathy in affected adults. A brief discussion of the neurological complications of Shigella infection and the yet undetermined role of Shiga toxin in producing neurotoxicity are presented.

Regulation of the Shiga-like toxin II operon in Escherichia coli

Investigations of the regulation of the bacteriophage-encoded Shiga-like toxin II (SLT-II) in Escherichia coli demonstrated that bacteriophages exhibit a regulatory impact on toxin production by two mechanisms. Firstly, replication of the toxin-converting bacteriophages brings about an increase in toxin production due to concomitant multiplication of toxin gene copies. Secondly, an influence of a phage-encoded regulatory molecule was demonstrated by using low-copy-number plasmid pADR-28, carrying a translational gene fusion between the promoter and proximal portion of slt-IIA and the structural gene for bacterial alkaline phosphatase (phoA). PhoA activity, reflecting the slt-II promoter activity, was significantly enhanced in E. coli strains which and been lysogenized with an SLT-I or SLT-II-converting bacteriophage (H-19B or 933W, respectively) or bacteriophage lambda. Both mechanisms are dependent on bacteriophage induction and hence are recA dependent. Moreover, the study revealed that the DNA-binding protein H-NS has a regulatory impact on both bacteriophage-mediated SLT-II synthesis and the activity of the slt-II promoter of plasmid pADR-28. While a slight impact of growth temperature on SLT-II expression was observed, no impact of either osmolarity, pH, oxygen tension, acetates, iron level, or utilized carbon source could be demonstrated.

Stimulation of gastrointestinal antibody to Shiga toxin by orogastric immunization in mice

Shiga toxin (ST) is a protein toxin of Shigella dysenteriae type 1, a causative agent of severe diarrhoea and dysentery. In this report we describe the gastrointestinal secretory antibody response of mice following orogastric immunization with ST. Gastrointestinal secretions were sampled by a gastrointestinal lavage technique weekly for 5 weeks after initial immunization. Assay of lavage samples by ELISA showed that mice vaccinated orogastrically with various doses of ST developed gastrointestinal antibody to ST in a dose-dependent manner. Serum anti-ST activity developed by 5 weeks after initial immunization. The ability of ST to act as a mucosal immune adjuvant was investigated by coadministration of ST and keyhole limpet haemocyanin. In contrast to cholera toxin, a potent adjuvant, ST did not demonstrate adjuvant activity. The mouse gastrointestinal lavage model could be useful for further analysis of the cellular basis of ST immunogenicity.

Comparison of Shiga-like toxin I B-subunit expression and localization in Escherichia coli and Vibrio cholerae by using trc or iron-regulated promoter systems

Shiga-like toxin I (SLT-I) B-subunit expression was examined by using the trc promoter in two different constructs, pSBC32 and pSBC54, in which 710 bp of DNA downstream of the B subunit in pSBC32 was deleted. The trc promoter in pSBC54 was replaced also with the SLT-I iron-regulated promoter to create a third plasmid, pSBC61. SLT-I B-subunit expression was examined from all three plasmids following transfer into Escherichia coli JM105 and the cholera toxin A-subunit gene deletion mutant Vibrio cholerae 0395-N1. The SLT-I B subunit was expressed from all constructs. pSBC61 was regulated by elemental iron and produced equivalent amounts of SLT-I B subunit from both E. coli and V. cholerae. In contrast to the cholera toxin B subunit, virtually all released into the medium, the SLT-I B subunit was predominantly cell associated in the pSBC61 constructs. Both pSBC32 and pSBC54 were inducible with isopropyl-beta-D-thiogalactopyranoside (IPTG) in the E. coli background but not the V. cholerae background; however, when E. coli cultures were allowed to grow for 24 h, the yield of SLT-I B subunit was not increased by IPTG induction. Both pSBC32 and -54 expressed more SLT-I B subunit in the V. cholerae host than in the E. coli host. Scale-up to a 9.9-liter fermentor culture of V. cholerae 0395 N1 (pSBC32) resulted in the isolation of 220 mg of SLT-I B. The purified B subunit was identical, in terms of binding to Vero cells, stoichiometry after chemical cross-linking, and ability to inhibit cytotoxicity of intact Shiga toxin, to native SLT-I B subunit from E. coli O157:H7.

Infectious Gastroenteritis

Infectious gastroenteritis currently constitutes the greatest source of morbidity and mortality among various age groups. Issues of focus for this article include establishing epidemiological determinants of risk for enteric infection, describing host factors that favor survival of the infecting enteric pathogen, defining pathophysiological mechanisms of diarrhea, and reviewing the therapeutic management of bacterial, protozoal, and viral infectious diarrhea.

A system for production and rapid purification of large amounts of the Shiga toxin/Shiga-like toxin I B subunit

We have constructed a plasmid expression vector (pSBC32) that encodes the B subunit of Shiga toxin/Shiga-like toxin I under control of the inducible trc promoter. The encoded B subunit is transported to the periplasmic space, allowing single-step purification of milligram amounts of this protein from periplasmic extracts by using receptor analog affinity chromatography. The purified B subunit interacts normally with both polyclonal antiserum to Shiga toxin and a monoclonal antibody specific for B subunit. B subunit purified in this system is pentameric (as in native holotoxin) and biologically active in blocking binding of Shiga holotoxin to HeLa cells. This expression system may allow rapid purification of sufficient amounts of Shiga toxin B subunit to attempt crystallization or to study its efficacy as a vaccine, either by itself or coupled to an appropriate polysaccharide antigen.

Recurrent seizures in children with Shigella-associated convulsions

Fifty-five children with Shigella-associated convulsions were followed prospectively to investigate their risk of subsequent febrile or nonfebrile seizures. The duration of the follow-up period was between 6.9 and 14.1 years (9.7 +/- 3.1 years). No case of nonfebrile seizures and only 2 cases (3%) of subsequent febrile seizures were observed during this period. We conclude that although febrile and Shigella-associated convulsions share many clinical features, the natural history of these two conditions seems to be distinctly different. Shigella-related convulsions are not associated with an increased incidence of subsequent febrile or nonfebrile convulsions.

The prognosis of convulsions during childhood shigellosis

We examined the long-term outcome in 111 children who had convulsions during shigellosis and were followed for 3-18 years after the incident. No deaths or persistent motor deficits occurred as sequellae. Poor coordination of fine hand movements were noted in 3.3% of the 92 children who had no pre-existing neurological abnormality. Only 1 child developed epilepsy by the age of 8 years. Of the children 15.7% had recurrent febrile seizures. The only risk factor identified for febrile seizures following convulsions in shigellosis was a previous history (P less than 0.01). These observations suggest that convulsions in shigellosis have a favourable prognosis, and do not necessitate long-term follow up.

Isolation and characterization of functional Shiga toxin subunits and renatured holotoxin

Shiga toxin is a protein toxin produced by Shigella dysenteriae type I strains. In this report we present a procedure for the separation of functionally intact toxin A and B chains and for their reconstitution to form biologically active molecules. In agreement with the findings of others, the isolated A chain was shown to be a potent in vitro inhibitor of eukaryotic protein synthesis. The isolated B chain bound to HeLa cells and competitively inhibited the binding and cytotoxic activity of holotoxin. These findings show that the functional role of the B chain is to recognize cell surface functional receptors. By labelling the B subunit alone, prior to renaturation of holotoxin, the polypeptide chains were shown to associate noncovalently with a stoichiometry of one A chain and five B chains.

Secretory immunoglobulin A response to Shiga toxin in rabbits: kinetics of the initial mucosal immune response and inhibition of toxicity in vitro and in vivo

Although the role of Shiga toxin in dysentery is unknown, the toxin is cytotoxic to HeLa cells, causes fluid secretion in rabbit intestine, and is lethal to rabbits and mice when injected parenterally. In the present study, rabbits received three weekly doses of Shiga toxin directly into chronically isolated ileal loops. Within a week, secretions from these loops contained immunoglobulin A (IgA) anti-Shiga toxin. The titer of IgA anti-Shiga toxin increased after weekly doses 2 and 3. Little IgG anti-Shiga toxin was present in loop secretions, although high titers of IgG anti-Shiga toxin were found in the sera. These loop secretions were able to neutralize the cytotoxic effects of Shiga toxin in the HeLa cell assay. The capacity to neutralize the cytotoxicity of the toxin correlated strongly with the IgA anti-Shiga toxin titer in these same secretions. Pooled immune loop secretions were also able to significantly reduce fluid accumulation in acutely ligated loops in rabbits, while loop secretions from control rabbits could not. Shiga toxin elicited a strong secretory IgA response upon application to the intestine. Further, the mucosal antibodies produced functioned to prevent the toxic effects of Shiga toxin both in vitro and in vivo.

Role of Shiga toxin in the pathogenesis of bacillary dysentery, studied by using a Tox- mutant of Shigella dysenteriae 1

A Tox- mutant of Shigella dysenteriae 1, SC501, was genetically engineered by cloning the Shiga toxin operon, inserting a cassette into the A subunit gene, and exchanging this in vitro-mutagenized sequence with the wild-type gene. SC501 produced a low amount of residual cytotoxicity which was not neutralized by a rabbit immune serum directed against Shiga toxin. Invasion of cultured cells demonstrated that Shiga toxin had no effect on the rate of intracellular growth of bacteria or on the rapid killing of invaded host cells. On the other hand, several significant differences were observed in macaque monkeys infected intragastrically with either the wild-type strain or its mutant. The production of Shiga toxin by the invading strain was correlated with the presence of blood within stools, a sharp drop in blood polymorphonuclear cells, and histopathological alterations, such as the destruction of capillary vessels within the connective tissue of the colonic mucosa, severe inflammatory vasculitis of the peritoneal mesothelium, and major efflux of inflammatory cells to the intestinal lumen. It is proposed that Shiga toxin influences the severity of bacillary dysentery by inducing colonic vascular damage, which accounts for bloody stools, intestinal ischemia, and inflation of a polymorphonuclear intestinal compartment during the infectious process.

Purification and some properties of a Vero toxin from Escherichia coli O157:H7 that is immunologically unrelated to Shiga toxin

A cytotoxin to Vero cells (Vero toxin) was purified from Escherichia coli O157:H7 isolated from a patient with hemorrhagic colitis by ammonium sulfate fractionation, DEAE-cellulose column chromatography, repeated chromatofocusing column chromatography and repeated high performance liquid chromatography. About 440 micrograms of purified Vero toxin was obtained from 12 liters of culture with a yield of about 22%. The purified Vero toxin showed similar cytotoxic activity to that of Shiga toxin to Vero cells and killed about 50% of the Vero cells at 1 pg. The activity was lost on heating the toxin at 80 degrees C for 10 minutes, but not at 60 degrees C for 10 minutes. The toxin also showed lethal toxicity to mice when injected intraperitoneally, the LD50 being 1 ng per mouse. The purified Vero toxin consisted of A and B subunits with molecular weights of about 35,000 and 10,700, respectively, which were slightly larger than those of Shiga toxin. On polyacrylamide gel disc electrophoresis, the mobility of the purified Vero toxin differed from that of Shiga toxin. The isoelectric point of the toxin was 4.1, which was also different from that of Shiga toxin (pI = 7.0). Furthermore, Vero toxin and Shiga toxin were found to be immunologically unrelated; anti-Vero toxin did not react with Shiga toxin, and similarly anti-Shiga toxin did not react with the Vero toxin in either the Ouchterlony double gel diffusion test or enzyme-linked immunosorbent assay. The Vero toxin purified in this work was found to be immunologically identical to VT2 and Shiga-like toxin II reported previously.

Purification and some properties of Shiga-like toxin from Escherichia coli O157:H7 that is immunologically identical to Shiga toxin

A cytotoxin to Vero cells (Shiga-like toxin), which was neutralized by antibody against purified Shiga toxin produced by Shigella dysenteriae 1, was purified from Escherichia coli O157:H7, isolated from a patient with hemorrhagic colitis. The purification procedure consisted of ammonium sulfate fractionation, DEAE-cellulose column chromatography, chromatofocusing column chromatography and high performance liquid chromatography. About 200 micrograms of purified Shiga-like toxin was obtained from cell extracts of 14 liters of culture with a yield of about 15%. The purified Shiga-like toxin showed identical physicochemical, biological and immunological properties to those of Shiga toxin. Purified Shiga-like toxin and Shiga toxin also had the same mobilities on polyacrylamide disc gel electrophoresis and polyacrylamide gel isoelectrofocusing. On sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis, purified Shiga-like toxin migrated as two bands corresponding to the A and B subunits, and these migrated to the same positions as A and B subunits of Shiga toxin. The amino acid composition of the purified Shiga-like toxin was also similar to that of Shiga toxin. The purified Shiga-like toxin showed various biological activities: lethal toxicity to mice when injected intraperitoneally, the LD50 being 30 ng per mouse; cytotoxicity to Vero cells, killing about 50% of the cells at 6 pg; and fluid accumulation in rabbit ileal loops at concentrations of more than 1.25 micrograms/loop. These values are comparable with those obtained with Shiga toxin. In an Ouchterlony double gel diffusion test, the lines formed by the purified Shiga-like toxin and Shiga toxin fused, indicating that the two toxins were immunologically identical.

Shigella dysenteriae 1 cytotoxin: periplasmic protein releasable by polymyxin B and osmotic shock

Treatment of Shigella dysenteriae 1 either with the antibiotic polymyxin B or by osmotic shock resulted in the release of 80 to 90% of the cytotoxin activity of the organism. Under the conditions employed, the release of toxin activity was accompanied by the appearance of a periplasmic enzyme, 5'-nucleotidase. There was no significant release of cytoplasmic contents, assessed by measurement of glucose-6-phosphate dehydrogenase activity. The release of cytotoxin and 5'-nucleotidase by polymyxin B were both dependent on the duration of incubation with, and the concentration of, the antibiotic. In terms of specific activity (cytotoxin activity per milligram of protein), the polymyxin B and osmotic shock extracts were 20- to 30-fold more active than crude toxin preparation derived from a whole-cell lysate. The data strongly support a periplasmic location for Shiga cytotoxin and the utility of the polymyxin B extraction to obtain starting material for toxin purification.

Protein synthesis in HeLa or Henle 407 cells infected with Shigella dysenteriae 1, Shigella flexneri 2a, or Salmonella typhimurium W118

The incorporation of [14C]leucine into protein was studied in two mammalian cell lines which had been infected with strains of Shigella dysenteriae 1, Shigella flexneri 2a, or Salmonella typhimurium W118. These cell lines differed in susceptibility to the effects of exogenously applied Shiga cytotoxin. All invasive shigella strains (which synthesize this toxin to a greater or lesser degree) were found to inhibit protein synthesis in both cell lines with equal efficiency. Leucine accumulation continued in these cells, but the labeled amino acid was preferentially incorporated into bacterial protein. S. typhimurium W118, which has not been shown to elaborate a Shiga-like toxin, had little effect on protein synthesis in infected host cells.

Aeromonas hydrophila in acute diarrheal disease: detection of enterotoxin and biotyping of strains

Eleven isolates of Aeromonas species from human stool cultures were found to produce enterotoxin activity as determined by assay of culture filtrates in rabbit intestinal loops and rabbit skin and on adrenal Y1 cells. Hemolysin(s) and a cytotoxic protein were found to interfere in all three assay systems but could be inactivated upon heating at 56 degrees C or by specific antihemolysin. Biotyping of each isolate was performed with a conventional test system and with API 50E and APIZYM kit systems (Analytab, Inc.). No single test of the more than 70 biochemical reactions investigated was found to correlate with enterotoxigenicity in the strains of Aeromonas hydrophila examined. All strains were found to belong to ideal phenotypes of A. hydrophila, but each strain possessed its own biochemical profile.

Pathogenesis of shigella diarrhea. Serum anticytotoxin antibody response produced by toxigenic and nontoxigenic Shigella dysenteriae 1

The serum antitoxin response to the cytotoxin contained in preparations of Shigella dysenteriae 1 (Shiga's bacillus) exotoxin was studied in natural and experimental infections of man. Natural infection resulted in the rapid appearance of toxin-neutralizing antibody, which disappeared some time between 9 and 18 mo after infection. Experimental infection of human volunteers provided the opportunity to study immunoglobulin class of the antibody in sera obtained serially from 7 to 50 days after infection. Neutralizing antibody was present only in the IgM fraction isolated by sucrose density gradient ultracentrifugation. This was confirmed by the use of solid-phase immunoaffinity chromatography. Even though the time-course and immunoglobulin class of the antitoxin antibody response was similar to that previously observed for anti-O polysaccharide antibody, the biologically active cytotoxin was shown to be highly susceptible to destruction by proteolytic enzymes. Sera from subjects infected with a virulent invasive chlorate-resistant Shiga mutant thought to be "nontoxigenic" also contained antibody which was similarly restricted to the IgM fraction. Biologically active cytotoxin was recovered when this mutant organism was grown in liquid media with controlled ion concentration. The mutant cytotoxin was heat labile, neutralized by antiwild-type cytotoxin antibody, and was separable by isoelectric focusing into two fractions with pI 7.2 and 6.1 like the wild-type toxin. These studies show that cytotoxin antigen is produced during in vivo infection with Shiga bacilli, resulting in a serum antitoxin antibody response. Without explanation is the restriction of the antibody to the IgM class and lack of evidence for an IgG antibody to the protein cytotoxin. Finally, mutant strain 725, previously designated "nontoxigenic," was shown to produce biologically active cytotoxin in vitro and, in experimentally infected volunteers, to result in a serum IgM antibody similar to that observed during infection with the wild-type strain.