Early acquisition of serum and saliva antibodies reactive to enteropathogenic Escherichia coli virulence-associated proteins by infants living in an endemic area

Secretory immunoglobulin A (sIgA) in saliva versus virulence proteins of enteropathogenic Escherichia coli (EPEC) in ill and colonized children

INTRODUCTION

We evaluated the presence of sIgA in saliva, versus Escherichia coli secreted proteins (Esp) related to the type III secretion system (T3SS), and its semi-quantitative concentration in children under 2 years-old (no longer breastfed) who were previously colonized or infected with enteropathogenic E. coli (EPEC).

METHODS

We analyzed the presence of sIgA in 40 children, who previously had positive cultures for EPEC associated (n=17) or not associated (n=23) with diarrhea, using the Western Blot technique versus E. coli secreted proteins: EspABCD. A semi-quantitative measurement of the reaction for each protein was made by its density peaks (OD).

RESULTS

We found sIgA versus all or some EspABCD proteins in both groups. However, the ill patients had higher concentrations of these antibodies than colonized patients.

DISCUSSION

The presence of sIgA in saliva could reflect an intestinal immune response and their levels could be related to a greater exposure and/or bacterial load.

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.

Placental and colostral transfer of antibodies reactive with enteropathogenic Escherichia coli intimins α, β, or γ

OBJECTIVE

Intimins are protein adhesins of enteropathogenic Escherichia coli and enterohemorrhagic E. coli capable of inducing attachment and effacement lesions in enterocytes. Anti-intimin antibodies are important for the protection from enteropathogenic E. coli and enterohemorrhagic E. coli infections because these antibodies inhibit bacterial adhesion and impair the initial step of the pathogenesis. We studied the transfer of maternal anti-intimin antibodies from healthy Brazilian mothers to their newborns through the placenta and colostrum.

METHODS

Serum immunoglobulin G and secretory immunoglobulin A antibodies against conserved and variable regions of intimins α, β, and γ were analyzed using an enzyme linked-immunosorbent assay in the blood and colostrum from 45 healthy women as well as cord blood serum samples from their newborns.

RESULTS

The concentrations of antibodies reactive with α intimin were significantly lower than those of anti-γ and anti-conserved intimin antibodies in the colostrum samples. IgG serum antibodies reactive with all the subtypes of intimins were transferred to the newborns, but the concentrations of anti-conserved intimin serum antibodies were significantly higher in mothers and newborns than concentrations of antibodies against variable regions. The patterns of IgG transfer from mothers to newborns were similar for all anti-intimin antibodies. These values are similar to the percentage transference of total IgG.

CONCLUSIONS

Anti-intimin antibodies are transferred from mothers to newborns through the placenta, and reinforce the protection provided by breastfeeding against diarrheagenic E. coli infections.

The intranasal vaccination of pregnant dams with Intimin and EspB confers protection in neonatal mice from Escherichia coli (EHEC) O157:H7 infection

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is responsible for intestinal disease and hemolytic uremic syndrome (HUS), a serious systemic complication which particularly affects children. In this study, we evaluated whether passive immunization protects from EHEC O157:H7 colonization and renal damage, by using a weaned BALB/c mouse model of infection. Recombinant proteins EspB and the carboxyl-terminal fragment of 280 amino acids of γ-intimin (γ-IntC280) were used in combination with a macrophage-activating lipopeptide-2 (MALP) adjuvant to immunize pregnant mice by the intranasal route. Neonatal mice were allowed to suckle vaccinated or sham-vaccinated dams until weaning when they were challenged by the oral route with a suspension of an E. coli O157:H7 Stx2+ strain. The excretion of the inoculated strain was followed for 72h. All vaccinated dams exhibited elevated serum IgG response against both γ-Int C280 and EspB. Passive immunization of newborn mice resulted in a significant increase in serum IgG titers against γ-Int C280 and a slight increase in EspB-specific antibodies. The neonates from vaccinated dams showed a significant reduction in EHEC O157:H7 colonization 48h post challenge. In addition, the level of plasma urea concentration, a marker of renal failure, was significantly higher in offsprings of sham-vaccinated mice. In conclusion, vaccination of pregnant dams with γ-Int C280 and EspB could reduce colonization and systemic toxicity of EHEC O157:H7 in their suckling offsprings.

Enterohemorrhagic Escherichia coli Pathogenesis and the Host Response

Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain capable of causing watery or bloody diarrhea, the latter termed hemorrhagic colitis, and hemolytic-uremic syndrome (HUS). HUS is defined as the simultaneous development of non-immune hemolytic anemia, thrombocytopenia, and acute renal failure. The mechanism by which EHEC bacteria colonize and cause severe colitis, followed by renal failure with activated blood cells, as well as neurological symptoms, involves the interaction of bacterial virulence factors and specific pathogen-associated molecular patterns with host cells as well as the host response. The innate immune host response comprises the release of antimicrobial peptides as well as cytokines and chemokines in addition to activation and/or injury to leukocytes, platelets, and erythrocytes and activation of the complement system. Some of the bacterial interactions with the host may be protective in nature, but, when excessive, contribute to extensive tissue injury, inflammation, and thrombosis, effects that may worsen the clinical outcome of EHEC infection. This article describes aspects of the host response occurring during EHEC infection and their effects on specific organs.

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 of mice against Shiga toxin 2 (Stx2)-associated damage by maternal immunization with a Brucella lumazine synthase-Stx2 B subunit chimera

Hemolytic-uremic syndrome (HUS) is defined as the triad of anemia, thrombocytopenia, and acute kidney injury. Enterohemorrhagic Shiga toxin (Stx)-producing Escherichia coli (EHEC), which causes a prodromal hemorrhagic enteritis, remains the most common etiology of the typical or epidemic form of HUS. Because no licensed vaccine or effective therapy is presently available for human use, we recently developed a novel immunogen based on the B subunit of Shiga toxin 2 (Stx2B) and the enzyme lumazine synthase from Brucella spp. (BLS) (BLS-Stx2B). The aim of this study was to analyze maternal immunization with BLS-Stx2B as a possible approach for transferring anti-Stx2 protection to the offspring. BALB/c female mice were immunized with BLS-Stx2B before mating. Both dams and pups presented comparable titers of anti-Stx2B antibodies in sera and fecal extracts. Moreover, pups were totally protected against a lethal dose of systemic Stx2 injection up to 2 to 3 months postpartum. In addition, pups were resistant to an oral challenge with an Stx2-producing EHEC strain at weaning and did not develop any symptomatology associated with Stx2 toxicity. Fostering experiments demonstrated that anti-Stx2B neutralizing IgG antibodies were transmitted through breast-feeding. Pups that survived the EHEC infection due to maternally transferred immunity prolonged an active and specific immune response that protected them against a subsequent challenge with intravenous Stx2. Our study shows that maternal immunization with BLS-Stx2B was very effective at promoting the transfer of specific antibodies, and suggests that preexposure of adult females to this immunogen could protect their offspring during the early phase of life.

Cross-reactive protection against enterohemorrhagic Escherichia coli infection by enteropathogenic E. coli in a mouse model

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) are related attaching and effacing (A/E) pathogens. The genes responsible for the A/E pathology are carried on a chromosomal pathogenicity island termed the locus of enterocyte effacement (LEE). Both pathogens share a high degree of homology in the LEE and additional O islands. EHEC prevalence is much lower in areas where EPEC is endemic. This may be due to the development of antibodies against common EPEC and EHEC antigens. This study investigated the hypothesis that EPEC infections may protect against EHEC infections. We used a mouse model to inoculate BALB/c mice intragastrically, first with EPEC and then with EHEC (E. coli O157:H7). Four control groups received either a nonpathogenic E. coli (NPEC) strain followed by EHEC (NPEC/EHEC), phosphate-buffered saline (PBS) followed by EHEC (PBS/EHEC), EPEC/PBS, or PBS/PBS. Mice were monitored for weight loss and symptoms. EPEC colonized the intestine after challenge, and mice developed serum antibodies to intimin and E. coli secreted protein B (encoded in the LEE). Prechallenge with an EPEC strain had a protective effect after EHEC infection, as only a few mice developed mild symptoms, from which they recovered. These mice had an increase in body weight similar to that in control animals, and tissue morphology exhibited mild intestinal changes and normal renal histology. All mice that were not prechallenged with the EPEC strain developed mild to severe symptoms after EHEC infection, with weight loss as well as intestinal and renal histopathological changes. These data suggest that EPEC may protect against EHEC infection in this mouse model.

Acquisition of serum antibodies reactive with enterohemorrhagic Escherichia coli virulence-associated factors by healthy Brazilian children and adults

BACKGROUND

Patients with hemorrhagic colitis or hemolytic uremic syndrome due to enterohemorrhagic Escherichia coli (EHEC) develop serum IgM and IgG response to lipopolysaccharide (LPS) and to virulence factors such as intimin. The small numbers of cases of diarrhea associated with EHEC strains in Brazil suggests a pre-existing immunity probably due to previous contact with diarrheagenic E. coli. Our aim was to evaluate the development of the serum antibody repertoire to EHEC virulence factors in Brazilian children and adults.

METHODS

Serum IgM and IgG antibodies were determined by enzyme-linked immunosorbent assay with LPS O111, LPS O26, and LPS O157 in 101 children between 2 months and 10 years of age and in 100 adult sera, by immunoblotting with protein membrane extracts and purified beta intimin; the ability of adult sera to neutralize Shiga toxin2 was also investigated.

RESULTS

Children older than 24 months had IgM concentrations reactive with the 3 LPS equivalent to those seen in the adult group, and significantly higher than the group of younger children (P < 0.05). Anti-O26 and anti-O157 LPS IgG concentrations were equivalent between the 2 groups of children and were significantly different from the adult group (P < 0.05). The anti-O111 LPS IgG levels in older children were intermediate between the younger group, and adults (P < 0.05). Immunoblotting revealed strong protein reactivity, including the conserved and variable regions of beta intimin and more than 50% of the adult samples neutralized Shiga toxin 2.

CONCLUSIONS

Our results demonstrate an increasing anti-LPS and antiprotein antibody response with age, which could provide protection against EHEC infections.

Immunization of mice with Lactobacillus casei expressing intimin fragments produces antibodies able to inhibit the adhesion of enteropathogenic Escherichia coli to cultivated epithelial cells

Enteropathogenic Escherichia coli (EPEC) are frequently isolated as a cause of infantile diarrhea in developing countries. Its pathogenicity is distinguished by histopathological alterations at the site of infection, known as attaching and effacing (A/E) lesions, in which bacterial virulence factors and host proteins participate. Intimin, a bacterial adhesin expressed by all EPEC described to date, is responsible for the intimate adherence of the bacteria to host cells and is essential for the formation of A/E lesions. Mucosal vaccination may represent an efficacious intervention to prevent EPEC infection and lower morbidity and mortality rates. Strategies for mucosal vaccinations that use lactic acid bacteria for the delivery of heterologous antigens rely on their safety profile and ability to stimulate the immune system. In the present work, we have constructed Lactobacillus casei strains expressing different fragments of intimin beta, a subtype that is frequently expressed by EPEC strains. Mucosal immunization of mice with L. casei expressing intimin fragments induced specific systemic and mucosal antibodies. These antibodies were able to recognize native intimin on the surface of EPEC and to inhibit in vitro EPEC binding to epithelial cells.

Protective and destructive innate immune responses to enteropathogenic Escherichia coli and related A/E pathogens

Enteropathogenic Escherichia coli, enterohemorrhagic E. coli (O157:H7) and Citrobacter rodentium are classified as attaching and effacing (A/E) pathogens based on their ability to adhere to intestinal epithelium, destroy microvilli and induce pedestal formation at the site of infection. A/E bacterial infections also cause acute diarrheal episodes and intestinal inflammation. The use of model systems has led to an understanding of the innate immune response to A/E pathogens. The innate immune system plays a protective role, initiating a productive antibody response, directly killing bacteria and inducing repair mechanisms following tissue damage caused by infection. However, hyperactivation of the innate immune system can have negative consequences, including exacerbated tissue destruction following neutrophil infiltration. Here we review how innate immune cell types, including neutrophils, macrophages and dendritic cells, orchestrate both protective and destructive responses. Such information is crucial for the development of therapeutics that can mitigate destructive inflammatory responses while accentuating those that are protective.

Passive immunity acquisition of maternal anti-enterohemorrhagic Escherichia coli (EHEC) O157:H7 IgG antibodies by the newborn

Enterohaemorrhagic Escherichia coli (EHEC) strains are among the main causes of haemorrhagic colitis (HC) and haemolytic-uremic syndrome (HUS) in industrialised countries. In Brazil, EHEC have been detected in the faeces of patients with non-bloody diarrhoea, though an association between EHEC and HUS has been detected recently. These observations suggest that there is a pre-existing immunity triggered by the contact with EHEC and other categories of bacteria, such as EPEC, that share similar virulence factors and to which our population is highly exposed. Our aim was to evaluate the placental transfer of IgG antibodies reactive to EHEC O157:H7 antigens. We evaluated 28 paired maternal and cord sera for the presence of IgG against EHEC O157:H7 protein antigens and IgG and IgM to O157 LPS employing ELISA and IB technique. Total IgG and IgM level analyses were also made. Anti-EHEC O157:H7 and anti-LPS O157 IgG antibody levels in cord sera were equivalent to those of their maternal sera. A good correlation between the mothers' anti-LPS O157 IgM and total IgM levels was found. Anti-LPS O157 IgM levels were higher than anti-LPS O157 IgG levels in the same samples, and anti-LPS IgM antibodies were not detected in cord sera. Identical patterns of recognition of bacterial protein antigens by specific IgG were found in the paired samples and the recombinant purified variable region of gamma intimin was specifically recognized by one paired maternal and cord sample. In conclusion, although the antibody profile varied among individuals, all paired cord and maternal serum samples showed an identical recognition pattern, indicating an efficient placental transfer of IgG antibodies reactive to EHEC O157:H7 antigens.

Systemic antibody response to diarrheagenic Escherichia coli and LPS O111, O157 and O55 in healthy Brazilian adults

Enterohaemorrhagic Escherichia coli (EHEC) can cause a variety of human illnesses ranging from uncomplicated diarrhoea to haemorrhagic colitis and haemolytic uremic syndrome. The serotype O157:H7 has been associated with numerous outbreaks worldwide, but in Brazil the infection is rare. Brazilian adults present antibodies reactive with the principal virulence factors of enteropathogenic E. coli (EPEC) that have many genetic and antigenic similarities with EHEC. Lipopolysaccharides (LPS) are components of outer membranes and important virulence factors of Gram-negative bacteria. LPS O111 is present in EPEC and EHEC strains. LPS O157 is found only in EHEC strains, but it has some structural similarities with LPS O55 present in EPEC strains. This study investigates the levels of IgG and IgM seric antibodies reactive with EHEC O157:H7, EHEC O111:H-, EPEC O111:H- and the levels of anti-LPS O111, LPS O157 and LPS O55 antibodies in healthy adults living in São Paulo, Brazil. The antibody levels were determined by an enzyme-linked immunosorbent assay for 100 individual serum samples, and the presence of anti-bacterial and anti-LPS seric antibodies was confirmed. Positive correlations were found among the three kinds of antibodies. The concentrations of IgM anti-LPS were significantly higher than those of IgG, and surprisingly, the concentrations of anti-LPS O157 were high in view of the infrequent isolation of O157 bacteria in Brazil. Our results suggest that there is a cross-reacting immunity to EHEC in the Brazilian population, which may be a result of the immunity to EPEC antigens. Alternatively, Brazilians may be exposed to EHEC more frequently than has previously been thought.

Human colostrum contains IgA antibodies reactive to colonization factors I and II of enterotoxigenicEscherichia coli

Diarrhea is an important cause of morbidity and mortality amongst infants of low socio-economic levels in developing countries and in travelers who visit such areas. Enterotoxigenic E. coli strains express two sets of virulence-associated factors: enterotoxins (heat-stable toxins or heat-labile toxins) and colonization factors. Studies have shown that breast-feeding protects infants against infectious diseases, such as diarrhea, as it presents a great variety of immunological components. The aim of this study was to analyze the reactivity of immunoglobulin A from human colostrum to colonization factor antigens I and II. The colostrum ability in preventing enterotoxigenic E. coli adhesion to Caco-2 cells was also evaluated. Colostrum samples were collected from 32 healthy women, and a human colostrum pool was prepared. Enterotoxigenic E. coli strains expressing colonization factor antigens I and II were utilized. The colostrum pool and individual samples showed variable antienterotoxigenic E. coli immunoglobulin A titers, that were reactive with colonization factor antigen I and CS1/CS3 (colonization factor antigen II). The human colostrum pool and individual samples inhibited enterotoxigenic E. coli colonization factor antigen I and II adhesion to Caco-2 cells, at variable levels, and this ability was a result of immunoglobulin A antibodies reactive to these colonization factors. The immunoglobulin A-depleted pool lost this inhibitory ability. As bacterial adhesion is the initial mechanism of enterotoxigenic E. coli infection, breast-feeding could protect the offspring against diarrhea caused by this agent.

Secretory immunoglobulin A obtained from pooled human colostrum and milk for oral passive immunization

Passive immunization is useful in cases of immunodeficiencies or infectious diseases, but usually seric gammaglobulin or hyperimmune sera are administered parenterally, providing good systemic immunization, though with low protection of the mucosal surfaces. The oral administration of secretory antibodies, especially surface immunoglobulin (SIg)A, which is perfectly adapted to the mucosal environment, would therefore, be preferable. The aim of the present study was to obtain a SIgA preparation from pooled human colostrum and milk, which should maintain the essential properties of the antibodies suitable for clinical oral administration. IgA preparations were obtained from colostrum and milk pools by salt precipitation. The final products were evaluated in terms of yield and purity, as well as antibody activity to bacterial antigens and toxins and inhibitory activity of bacterial adhesion to epithelial cells. The best yield and purity were achieved when the colostrum pool was used as a source of IgA; the final product showed very few bands of protein contamination. The IgA preparations preserved the antibody reactivity against various microbial antigens, well comparable with the reactivity exhibited by the original milk and colostrum pools. SIgA preparations were able to inhibit greatly the adhesion of enteropathogenic Escherichia coli to Hep-2 cells and the invasion of enteroinvasive E. coli. These promising results show the feasibility of obtaining SIgA suitable for oral use, which may in future be administered to immunodeficient patients with gastrointestinal manifestations, from human colostrum and milk.

Colostrum from healthy Brazilian women inhibits adhesion and contains IgA antibodies reactive with Shiga toxin-producing Escherichia coli

Although Shiga toxin-producing Escherichia coli (STEC) has been isolated in Brazil, severe manifestations of the infection, such as haemorrhagic colitis and haemolytic-uraemic syndrome, are extremely rare in our population. Enteropathogenic Escherichia coli (EPEC) is the main aetiological agent of acute infantile diarrhoea in Brazil. There are many similarities between STEC and EPEC, such as the ability to produce attaching and effacing (A/E) lesions and some virulence-associated factors. Our aim was to investigate the presence of anti-STEC antibodies in healthy people living in an EPEC endemic area. Colostrum samples collected from 51 women living in low socio-economic conditions were analysed. Two STEC strains: O111:H- (Stx1) and O157:H7 (Stx2), and one EPEC strain (O111:H-) were used in the bacterial adhesion assays to HEp-2 cells, in the Stx1 and Stx2 cytotoxicity assays on Vero cells, in immunoblotting and in ELISA assays. All the samples strongly inhibited the adhesion of the three strains and contained SIgA antibodies reactive with antigens of EPEC O111:H-, STEC O111:H- and STEC O157:H7, mainly STEC and EPEC 94 kDa adhesin intimin. High titres of anti-LPS O111 antibodies were found in many samples. Nevertheless, the cytotoxic effect of both Stx1 and Stx2 on Vero cells was not neutralised by any sample.

CONCLUSION

Our results suggest that Brazilian people may be exposed to Shiga toxin-producing Escherichia colimore frequently than previously thought or alternatively there may be a cross reactive immunity between enteropathogenic Escherichia coliand Shiga toxin-producing Escherichia coli.