Cross-protection against challenge by intravenous Escherichia coli verocytotoxin 1 (VT1) in rabbits immunized with VT2 toxoid

Factors in the emergence of serious human infections associated with highly pathogenic strains of shiga toxin-producing Escherichia coli

The appearance of highly pathogenic strains of Shiga toxin (Stx)-producingEscherichia. coli (STEC) has owed largely to the acquisition of Stx-encoding prophages by strains of E. coli that have pre-existing potential as enteric pathogens, such as atypical enteropathogenic E. coli (aEPEC) and enteroaggregative E. coli (EAEC). However, while high pathogenic potential is necessary, it is not sufficient for such strains to have a serious public health impact (i.e., large outbreaks, many cases of HUS, or both). To do so requires susceptible hosts and additional elements related to transmission, such as, socio-economic, societal, and lifestyle, factors. Two examples are discussed to illustrate this. The factors involved in the emergence of serious disease associated with E. coli O157:H7 in the 1980s probably included a massive increase in population exposure to this pathogen, likely as a result of the introduction of factory farming of cattle in the 1960s, and the development and wide patronage of fast food hamburger restaurants, and, potentially, waning immunity to intimin as a result of the reduction of incidence of enteropathogenic E. coli (EPEC) infection. In the devastating outbreak of Stx2-positiveEAEC O104:H4 in 2011, the wide distribution of the proposed vehicle of transmission, imported fenugreek seeds, was decisive in the exposure of a large population in Central Europe to this pathogen. Contributing factors likely included a preference for eating raw sprouts as a healthy food choice by the affected cases, many of whom were women. Low population levels of immunity to Stx2 probably contributed to the severe clinical outcome. A better understanding of the factors responsible for the emergence of potentially dangerous STEC pathogens as well as of extensive and serious disease associated with them can enhance public health strategies to respond to them.

Mucosal Immune Responses to Escherichia coli and Salmonella Infections

The best-characterized mucosa-associated lymphoid tissue (MALT), and also the most relevant for this review, is the gastrointestinal-associated lymphoid tissue (GALT). The review reviews our understanding of the importance of mucosal immune responses in resisting infections caused by E. coli and Salmonella spp. It focuses on the major human E. coli infections and discusses whether antigen-specific mucosal immune responses are important for resistance against primary infection or reinfection by pathogenic E. coli. It analyzes human data on mucosal immunity against E. coli, a growing body of data of mucosal responses in food production animals and other natural hosts of E. coli, and more recent experimental studies in mice carrying defined deletions in genes encoding specific immunological effectors, to show that there may be considerable conservation of the effective host mucosal immune response against this pathogen. The species Salmonella enterica contains a number of serovars that include pathogens of both humans and animals; these bacteria are frequently host specific and may cause different diseases in different hosts. Ingestion of various Salmonella serovars, such as Typhimurium, results in localized infections of the small intestine leading to gastroenteritis in humans, whereas ingestion of serovar Typhi results in systemic infection and enteric fever. Serovar Typhi infects only humans, and the review discusses the mucosal immune responses against serovar Typhi, focusing on the responses in humans and in the mouse typhoid fever model.

Protection by a recombinant Mycobacterium bovis Bacillus Calmette-Guerin vaccine expressing Shiga toxin 2 B subunit against Shiga toxin-producing Escherichia coli in mice

We have developed a novel vaccine against Shiga toxin (Stx)-producing Escherichia coli (STEC) infection using a recombinant Mycobacterium bovis BCG (rBCG) system. Two intraperitoneal vaccinations with rBCG expressing the Stx2 B subunit (Stx2B) resulted in an increase of protective serum IgG and mucosal IgA responses to Stx2B in BALB/c mice. When orally challenged with 10(3) CFU of STEC strain B2F1 (O91: H21), the immunized mice survived statistically significantly longer than the nonvaccinated mice. We suggest that intraperitoneal immunization with rBCG expressing Stx2B would be a potential vaccine strategy for STEC.

Host and pathogen determinants of verocytotoxin-producing Escherichia coli-associated hemolytic uremic syndrome

Verocytotoxin (VT)-producing Escherichia coli (VTEC) infection is associated with a spectrum of clinical manifestations that includes diarrhea, hemorrhagic colitis, and the hemolytic uremic syndrome (HUS). The occurrence of HUS in a minority of individuals in outbreaks of VTEC infection is a function of several pathogen and host factors. Pathogen factors include the inoculum size and serotype of the infecting strain, horizontally acquired genetic elements known as pathogenicity islands, and probably the VT type. Host factors that increase the risk of developing HUS include age, pre-existing immunity, gastric acidity, the use of antibiotics and anti-motility agents, and, probably, stress and genetic factors that modulate host response to infection, such as innate immunity and toxin receptor type, expression, and distribution. A better understanding of the pathogen and host determinants of HUS can aid in the development of more effective public health strategies to reduce the risk of developing HUS.

ACTIVITIES OF AQUEOUS EXTRACTS OF MALLOTUS OPPOSITIFOLIUM ON SHIGELLA DYSENTERIAE A1-INDUCED DIARRHOEA IN RATS

1. Mallotus oppositifolium is reported to possess medicinal properties and is traditionally used in Cameroon for the treatment of diarrhoea. In the present study, we have evaluated the acute toxicity, in vitro antibacterial and in vivo antidiarrhoeal effects of an aqueous extract of these plant leaves. 2. Shigella dysenteriae A(1) (Sd1)-induced diarrhoeal rats were obtained by oral administration of increasing densities of the Sd1 strain isolated from bloody diarrhoea occurring in East Cameroon. When diarrhoea appeared, rats were treated for 5 consecutive days with 120, 240 or 360 mg/kg extract or norfloxacin (5.7 mg/kg). The weight and frequencies of faeces, as well as the number of Sd1, were assessed during the treatment period and the death rate was recorded. 3. The M. oppositifolium extract was not toxic. In vitro, the minimal inhibitory and minimal bactericidal concentrations of the extracts were 1,172 and 9,375 microg/mL, respectively. In vivo, 12 x 10(8) Sd1 provoked diarrhoea within 24 h, which was characterized by soft or liquid stools, that were moulded, smooth and mucus or blood coated. Diarrhoea went along with an increase in faeces weight and frequency (P < 0.001 by the 3rd day), as well as an increase in the bacterial population to a maximum on the 2nd day after infection (P < 0.05). The death rate was 67% by day 6. 4. Whereas norfloxacin significantly (P < 0.01) reduced Sd1 growth, M. oppositifolium extracts (240 and 360 mg/kg) restored bacterial growth to its initial density and no deaths were recorded. There was a significant (P < 0.05) reduction in stools weight and frequency with 240 mg/kg extract. 5. The results suggest that M. oppositifolium leaves could be a therapeutic alternative for bacterial aetiological diarrhoea in Central Africa, where multidrug supply and access to modern health centres are public health problems.

Protection against hemorrhagic colitis in an animal model by oral immunization with isogeneic rabbit enteropathogenic Escherichia coli attenuated by truncating intimin

Strains of Shiga toxin (Stx)-producing Escherichia coli, also called enterohemorrhagic E. coli (EHEC), are important food-borne pathogens for humans. Most EHEC strains intimately adhere to the intestinal mucosa in a characteristic attaching and effacing (A/E) pattern, which is mediated by the bacterial adhesin intimin. Subsequent release of Stx1 and/or Stx2 leads to the frequent development of hemorrhagic colitis and, less commonly, to hemolytic-uremic syndrome. The aim of the present study was to develop an attenuated A/E E. coli strain for use as a vaccine against EHEC infection encoding a truncated intimin lacking adhesive capacity, but which would still express somatic antigens, other products of the locus of enterocyte effacement pathogenicity island, and an immunogenic remnant of the intimin molecule. A single-nucleotide deletion was generated in the eae gene in the prototype rabbit A/E E. coli strain RDEC-1 (O15:H-), which resulted in truncation of intimin by 81 C-terminal residues (860 to 939 amino acids) containing a disulfide loop. Inoculation of rabbits with large doses of the truncated intimin mutant (RDEC-1Deltaeae(860-939)) was well tolerated, as observed by the absence of clinical signs of disease or evidence of intestinal A/E lesions. The efficacy of RDEC-1Deltaeae(860-939) as a vaccine was evaluated by orogastric inoculation of rabbits with RDEC-1Deltaeae(860-939) followed by challenge with the virulent strain RDEC-H19A, an Stx1-producing derivative of wild-type RDEC-1 capable of inducing hemorrhagic colitis in rabbits. Following RDEC-H19A challenge, nonimmunized control rabbits exhibited characteristic weight loss with watery to bloody diarrhea and demonstrated intimate bacterial attachment, effacement of microvilli, submucosal edema, mucosal heterophile infiltrates, and Shiga toxin-induced vascular lesions. In contrast, the RDEC-1Deltaeae(860-939)-immunized rabbits showed no clinical signs of disease, maintained normal weight gain, had reduced fecal shedding of challenge organisms, and showed an absence of gross or microscopic lesions in the intestinal mucosa. Serum antibodies specific to intimin were detected among rabbits immunized with RDEC-1Deltaeae(860-939), indicating that truncation of the intimin functional domain not only attenuated bacterial virulence, but also retained at least some of the immunogenicity of native intimin. Although it is not possible to gauge the exact contribution of residual intimin immunity to protection, this attenuation strategy for A/E E. coli strains shows promise for the development of effective vaccines to prevent EHEC infection in humans and animals.

Marasmius oreades lectin induces renal thrombotic microangiopathic lesions

The present studies demonstrate that infusion of a type B specific lectin derived from the mushroom Marasmius oreades (MOA) into mice binds selectively to the glomerular endothelial cells via surface carbohydrate moieties resulting in cell injury and death associated with platelet-fibrin thrombi. This selective MOA binding to the endothelial cells can be abrogated by a sugar specific for the carbohydrate sequence. Hemolytic-Uremic Syndrome (HUS) and the closely associated Thrombotic Thrombocytopenic Purpura (TTP) are diseases associated with widespread microvascular injury in various organs. Clinically, these diseases are associated with microangiopathic hemolytic anemia and thrombocytopenia. The kidney glomerulus is a primary target of this microvascular injury. There are many underlying etiologies including bacterial toxins. Experimentally, such toxins injure endothelial cells in vitro but in vivo studies have failed to reproduce the characteristic renal pathology. We suggest that MOA-induced glomerular microangiopathic injury could be used to study the pathophysiology of endothelial cell injury as related to glomerular microangiopathic injury.

Protection against Shiga toxin 1 challenge by immunization of mice with purified mutant Shiga toxin 1

Shiga toxin 1 (Stx1) of enterohemorrhagic Escherichia coli O157:H7 was cloned, and four mutant Stx1s were constructed by site-directed mutagenesis with PCR. The wild-type and mutant Stx1s with amino acid replacements at positions 167 and 170 of the A subunit were purified by one-step affinity chromatography with commercially available Globotriose Fractogel, and the mutant Stxs were used for the immunization of mice. The mutant toxins were nontoxic to Vero cells in vitro and to mice in vivo and induced the immunoglobulin G antibody against the wild-type Stx1, which neutralized the cytotoxicity of Stx1. The induced antibody titers depended on the mutation at position 170 of the A subunit. The mice immunized with the mutant Stx1s were protected against a challenge of approximately 100 times the 50% lethal dose of the wild-type Stx1, suggesting that the mutant toxins are good candidates for toxoid vaccines for infection by Stx1-producing E. coli.