Protection against Escherichia coli K1 infection in newborn rats by antibody to K1 capsular polysaccharide antigen

Cerclage prevents ascending intrauterine infection in pregnant mice

BACKGROUND

The treatment for cervical insufficiency is cerclage surgery. Although cerclage is a common therapy for prevention of preterm birth, there is no consensus about its mechanism of efficacy. Previous investigators have hypothesized that cerclage prevents preterm birth by improving the cervical barrier to ascending infection. However, this hypothesis is difficult to study in human pregnancy.

OBJECTIVE

In a mouse model of ascending infection, we hypothesized that a cerclage improves the cervical barrier leading to decreased ascending intrauterine infection and inflammation. An abdominal cerclage was studied because a vaginal cerclage is not feasible in mice.

STUDY DESIGN

To perform an abdominal cerclage, laparotomy was performed on timed, pregnant C57BL/6 mice on gestational day 10 (E10). A 6-0 silk suture was placed around the cervix just below the junction of the 2 uterine horns. Sham controls received the same surgery, but no cerclage was placed. To track ascending infection nonpathogenic E coli K12 was genetically modified to express bioluminescence. On E15, bioluminescent E coli K12 (20 μL of 1×109 bacteria) was inoculated into the vagina. Whole-body bioluminescence imaging was performed 0.5 hours and 24 hours after inoculation. To assess intrauterine inflammation, pathogenic E coli K1 was used. On E15, bacterial inoculums of E coli K1 (20 μL of 1×104 bacteria) were vaginally administered. Samples of uterus, placenta, and fetal membranes were collected 24 hours after inoculation. Gene expression of inflammation-related proteins was compared between 3 groups: (1) sham control surgery + inoculation of phosphate-buffered saline (PBS), (2) sham control surgery + inoculation of E coli K1, and (3) cerclage surgery + inoculation of E coli K1.

RESULTS

Abdominal cerclage was well tolerated. No cases of preterm birth were seen following abdominal cerclage. Whole-body bioluminescent imaging performed 0.5 hours post inoculation showed a strong luminescence signal in the vaginal region of mice in both control and experimental groups indicating successful bacteria inoculation. Twenty-four hours after inoculation, bioluminescent signal was seen ascending into the uterine horns in all control mice. However, in mice with abdominal cerclages, no bioluminescent signal was seen after 24 hours. When the reproductive tissues were imaged separately in control mice, strong bioluminescence signal was detected in the placenta, fetal membranes, and uterus. Gene expression studies showed that cerclage significantly decreased the expression of inflammatory proteins induced by E coli K1 in the uterus, placenta, and fetal membranes.

CONCLUSION

In this mouse model of ascending intrauterine infection, abdominal cerclage prevented ascending infection of E coli. In addition, abdominal cerclage prevented expression of inflammatory cytokines in the uterus, placenta, and membranes of mice. The study provides evidence for a potential mechanism of cerclage success in human pregnancy.

Phage Targeting Neonatal Meningitis E. coli K1 In Vitro in the Intestinal Microbiota of Pregnant Donors and Impact on Bacterial Populations

Escherichia coli K1 is a leading cause of neonatal meningitis. The asymptomatic carriage of these strains in the maternal intestinal microbiota constitutes a risk of vertical transmission to the infant at birth. The aim of this work was to evaluate the efficacy of phage therapy against E. coli K1 in an intestinal environment and its impact on the intestinal microbiota. For this purpose, three independent experiments were conducted on the SHIME® system, the first one with only the phage vB_EcoP_K1_ULINTec4, the second experiment with only E. coli K1 and the last experiment with both E. coli K1 and the phage. Microbiota monitoring was performed using metagenetics, qPCR, SCFA analysis and the induction of AhR. The results showed that phage vB_EcoP_K1_ULINTec4, inoculated alone, was progressively cleared by the system and replicates in the presence of its host. E. coli K1 persisted in the microbiota but decreased in the presence of the phage. The impact on the microbiota was revealed to be donor dependent, and the bacterial populations were not dramatically affected by vB_K1_ULINTec4, either alone or with its host. In conclusion, these experiments showed that the phage was able to infect the E. coli K1 in the system but did not completely eliminate the bacterial load.

Preconceptual Priming Overrides Susceptibility to Escherichia coli Systemic Infection during Pregnancy

Maternal sepsis is a leading cause of morbidity and mortality during pregnancy. Escherichia coli is a primary cause of bacteremia in women and occurs more frequently during pregnancy. Several key outstanding questions remain regarding how to identify women at highest infection risk and how to boost immunity against E. coli infection during pregnancy. Here, we show that pregnancy-induced susceptibility to E. coli systemic infection extends to rodents as a model of human infection. Mice infected during pregnancy contain >100-fold-more recoverable bacteria in target tissues than nonpregnant controls. Infection leads to near complete fetal wastage that parallels placental plus congenital fetal invasion. Susceptibility in maternal tissues positively correlates with the number of concepti, suggesting important contributions by expanded placental-fetal target tissue. Remarkably, these pregnancy-induced susceptibility phenotypes are also efficiently overturned in mice with resolved sublethal infection prior to pregnancy. Preconceptual infection primes the accumulation of E. coli-specific IgG and IgM antibodies, and adoptive transfer of serum containing these antibodies to naive recipient mice protects against fetal wastage. Together, these results suggest that the lack of E. coli immunity may help discriminate individuals at risk during pregnancy, and that overriding susceptibility to E. coli prenatal infection by preconceptual priming is a potential strategy for boosting immunity in this physiological window of vulnerability.IMPORTANCE Pregnancy makes women especially vulnerable to infection. The most common cause of bloodstream infection during pregnancy is by a bacterium called Escherichia coli This bacterium is a very common cause of bloodstream infection, not just during pregnancy but in all individuals, from newborn babies to the elderly, probably because it is always present in our intestine and can intermittently invade through this mucosal barrier. We first show that pregnancy in animals also makes them more susceptible to E. coli bloodstream infection. This is important because many of the dominant factors likely to control differences in human infection susceptibility can be property controlled for only in animals. Despite this vulnerability induced by pregnancy, we also show that animals with resolved E. coli infection are protected against reinfection during pregnancy, including having resistance to most infection-induced pregnancy complications. Protection against reinfection is mediated by antibodies that can be measured in the blood. This information may help to explain why most women do not develop E. coli infection during pregnancy, enabling new approaches for identifying those at especially high risk of infection and strategies for preventing infection during pregnancy.

Review: Evidence against the hypothesis that antibodies to the inner core of lipopolysaccharides in antisera raised by immunization with enterobacterial deep-rough mutants confer broad-spectrum protection during Gram-negative bacterial sepsis

Antisera to rough enterobacterial mutants of chemotypes Ra, Rc, and Re have been reported to confer broad-spectrum protection against wild-type smooth strains. It has been hypothesized that binding and neutralization of lipopolysaccharides (LPS) by antibodies to common core epitopes underlies such protection. This review summarizes experiments by our laboratory and others that do not confirm this concept and proposes reasons for the divergent results. Studies indicating broad-spectrum protection by rough-mutant antisera often had defects in experimental design or methodology. These include the failure: (i) to use matched pre- and postimmune sera from the same donors to control for variable protective activity of normal sera; (ii) to exclude the role of natural and polyclonally stimulated antibodies with proven protective activity against the infecting bacterial strain (e.g. O-specific, capsular, Pseudomonas exotoxin A); (iii) to exclude protective effects of acute-phase serum factors; (iv) to exclude protective effects of endotoxin contamination after adsorption or fractionation of antibody preparations; (v) to use non-boiled bacteria and LPS not subjected to acid-hydrolysis or gel-fractionation, and to exclude nonspecific adsorption, to demonstrate physiologically meaningful binding of rough-mutant antibodies to smooth enterobacteria and their LPS.

A conjugate vaccine composed of a heat shock protein 60 T-cell epitope peptide (p458) and Neisseria meningitidis type B capsular polysaccharide

Neisseria meningitidis type B is a major world-health problem. The Meningococcus type B capsular polysaccharide (MnB) is very poorly immunogenic and no vaccine to the antigen exists. Here, we conjugated the MnB to a T-cell carrier peptide (p458) derived from the self-60kDa heat shock protein molecule. The conjugate vaccine was effective in inducing long-lasting IgG antibodies to the MnB antigen in mice. The vaccine was also immunogenic when injected in PBS. Thus, the p458 carrier peptide can induce T-cell help for the switch to IgG Ab to the MnB antigen.

Preclinical evaluation of group B Neisseria meningitidis and Escherichia coli K92 capsular polysaccharide-protein conjugate vaccines in juvenile rhesus monkeys

We reported the first use of group B meningococcal conjugate vaccines in a nonhuman primate model (S. J. N. Devi, C. E. Frasch, W. Zollinger, and P. J. Snoy, p. 427-429, in J. S. Evans, S. E. Yost, M. C. J. Maiden, and I. M. Feavers, ed., Proceedings of the Ninth International Pathogenic Neisseria Conference, 1994). Three different group B Neisseria meningitidis capsular polysaccharide (B PS)-protein conjugate vaccines and an Escherichia coli K92 capsular polysaccharide-tetanus toxoid (K92-TT) conjugate vaccine are here evaluated for safety and relative immunogenicities in juvenile rhesus monkeys with or without adjuvants. Monkeys were immunized intramuscularly with either B PS-cross-reactive material 197 conjugate, B PS-outer membrane vesicle (B-OMV) conjugate, or N-propionylated B PS-outer membrane protein 3 (N-pr. B-OMP3) conjugate vaccine with or without adjuvants at weeks 0, 6, and 14. A control group of monkeys received one injection of the purified B PS alone, and another group received three injections of B PS noncovalently complexed with OMV. Antibody responses as measured by enzyme-linked immunosorbent assay varied among individual monkeys. All vaccines except B PS and the K92-TT conjugate elicited a twofold or greater increase in total B PS antibodies after one immunization. All vaccines, including the K92-TT conjugate, elicited a rise in geometric mean B PS antibody levels of ninefold or more over the preimmune levels following the third immunization. Antibodies elicited by N-pr. B-OMP3 and B-OMV conjugates were directed to the N-propionylated or to the spacer-containing B PS antigens as well as to the native B PS complexed with methylated human serum albumin. None of the vaccines caused discernible safety-related symptoms.

The elusive determinants of bacterial interference with non-specific host defences

The identification of the determinants of bacterial interference with non-specific host defences during the early stages of infection is approached rather than attained. Recognizing a relevant biological property (e.g. resistance to phagocytosis) by an in vitro test and associating bacterial surface components with it are relatively easy. Proving causation, however, is usually not completed because the biological test is complex and the surface component(s) act only in situ . Nevertheless, evidence in addition to mere association can be sought to show that a putative determinant is strongly implicated in biological activity. Even then, proving that the biological activity concerned is relevant to infection in vivo , and that the putative determinant is produced there, is often not accomplished. Again, however, distinction can be made between those cases probably relevant in vivo and those only possibly so. Finally, bacteria grown in vitro can be deficient in some of the determinants of pathogenicity expressed during infection, and this situation requires the study of organisms grown in vivo . These points are discussed and then illustrated in a brief survey of the activities of many pathogenic bacteria and a description of recent work on the resistance of gonococci to killing by human serum and phagocytes.

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.

Use of hybridoma immunoglobulin switch variants in the analysis of the protective properties of anti-lipopolysaccharide antibodies in Escherichia coli K1 infection

Functional properties of rat immunoglobulins obtained from hybridoma isotype switch variants were studied in vivo in a rat model for neonatal bacterial sepsis. Escherichia coli 018:K1, a common cause of human neonatal sepsis and meningitis, was injected intravenously into 6-day-old rats after incubation with 018-specific antibodies IgM, IgG1, IgG2a, IgG2b, IgG2c, IgE and IgA. The clearance of bacteria treated with saline or IgE was low, whereas monoclonal antibodies of other isotypes triggered hepatic sequestration and killing of the K1 E. coli cells. All four IgG subclasses were more efficient than IgM and IgA. Comparable results were obtained upon injecting antibodies into rats with an established fulminating bacteraemia. IgM was inactive in animals depleted of complement with cobra-venom factor (CVF), whereas IgG2b was able to trigger hepatic clearance independently of complement.

Heterologous protection against invasive Escherichia coli K1 disease in newborn rats by maternal immunization with purified mannose-sensitive pili

Heterologous protection against Escherichia coli K1 bacteremia with antibody to purified mannose-sensitive (MS) pili was demonstrated in a neonatal rat model. The serological relatedness of purified MS pili from 17 E. coli K1 clinical isolates was examined by an enzyme-linked immunosorbent assay. Five pilus serogroups were identified, with the pili in each group showing 50% or greater cross-reactivity with the typing serum of the group. The MS pili from 12 of 17 (70%) strains belonged to just two serogroups. Pregnant Sprague-Dawley rats (dams) were immunized with purified pili, and their newborns (pups) were challenged with heterologous E. coli. Bacteremia was significantly reduced when the pili used for immunization were from the same serogroup as the pili expressed by the challenge bacteria. Thus, immunization with C94 pili and challenge with E03 (71% cross-reactivity) or E04 (50% cross-reactivity) resulted in bacteremia rates of 12 of 17 (17%) versus 51 of 79 (65%) in controls and 0 of 75 (0%) versus 28 of 70 (40%) in controls, respectively (P less than 0.001 for each comparison). With lower cross-reactivity, less protection was observed (P less than 0.05 for 22 to 37% pilus serological relatedness). No protection was seen in pups suckled by dams immunized with MS pili having only 5% serological relatedness to the pili on the challenge strain.

Passive transfer of meningococcal group B polysaccharide antibodies to the offspring of pregnant rabbits and their protective role against infection with Escherichia coli K1

Pregnant rabbits vaccinated with meningococcal group B polysaccharide complexed to outer membrane proteins (serotype 6) responded to produce IgG, IgM and IgA anti-B polysaccharide antibodies, which were passively transferred to the offspring (IgG preferentially) and could be detected in their sera immediately after birth. These antibody levels were sustained in the mothers but diminished in the offspring to background levels at day 22 after birth. In a subsequent experiment, rabbits immunized with the group B vaccine had offspring that proved considerably more resistant to infection with Escherichia coli K1 than the control litters from non-immune mothers. Although not complete, protection was statistically of high significance and correlated well with the anti-B polysaccharide titres obtained in the mothers.

Effect of immunization with Escherichia coli K1 antigen on the course of experimental infection of the urinary tract of the rat

The influence of vaccination with an immunogenic K1 antigen of Escherichia coli on the course of pyelonephritis induced experimentally in rats by infection with Escherichia coli O2:K1:H4 was investigated. The immunogenic properties of K1 antigen are poor. A conjugate of K1 antigen with bovine serum albumin (BSA) was therefore tested. Preliminary experiments showed that the K1-BSA conjugate is immunogenic. Renal inflammatory activity in rats after retrograde infection was significantly reduced after vaccination of the animals with K1-BSA conjugate within six weeks of infection.

A human monoclonal macroglobulin with specificity for alpha(2----8)-linked poly-N-acetyl neuraminic acid, the capsular polysaccharide of group B meningococci and Escherichia coli K1, which crossreacts with polynucleotides and with denatured DNA

We have described an IgM antibody from a patient with macroglobulinemia specifically reacting with poly-alpha(2----8)N-acetyl neuraminic acid (NeuNAc) the capsular polysaccharide of two important human pathogens, group B meningococcus and E. coli K1. This antibody has a narrowly defined specificity in its interactions with polysaccharides, being unable to bind poly-alpha(2----9)NeuNAc or alternating poly-alpha(2----8)alpha(2----9)NeuNAc. However, it shows interesting crossreactivity with seemingly unrelated polynucleotides and denatured DNA, supporting the hypothesis that charged groups with a given spacing may determine the specificity of antigen-antibody interactions on otherwise dissimilar molecular structures. Despite the crossreactivity with denatured DNA and polynucleotides, the antibody does not appear to have adverse effects in the patient. The antibody protects newborn rats against E. coli K1 infection, as well as the standard horse antiserum H46, and one would expect it to prove useful in humans as an adjunct to antibiotic therapy in infections with group B meningococcus and E. coli K1. We have attempted to clone the antibody-producing cells from peripheral blood, and have shown that the relevant cells are present and can be cultured.

Ontogeny of macrophage-mediated protection against Listeria monocytogenes

We investigated the ontogenic development of macrophage functions which are important in the expression of host defense against infection by Listeria monocytogenes. Macrophage functions, including accumulation in response to local stimuli, chemotaxis in vitro, and intracellular killing, as well as number of macrophages, were examined by using mice 1, 2, 3, 4, and 8 weeks old. The number of peritoneal macrophages was extremely low in younger mice even when their body weights were taken into consideration. Macrophage accumulation in response to infectious stimulus with viable listeria was poor in younger mice and showed an age-dependent development. In younger groups, chemotaxis in vitro was as immature as chemotaxis in vivo. In 1- and 2-week-old mice, macrophages did not show any intracellular killing activity against L. monocytogenes, but killing was observed in mice over 3 weeks of age. These functions developed in an age-dependent manner and reached the 8-week-old adult level after the mice were 4 weeks of age. In adult mice, these macrophage functions were shown to be enhanced after immunization with viable listeria; however, such an immunization-induced enhancement was very poor in the younger groups of mice. Protection judged by mortality and in vivo bacterial growth was weaker in the younger groups against both primary and secondary challenges. In vivo protection against L. monocytogenes seemed to develop in the same age-dependent manner as the development of macrophage functions. These results indicate that age-dependent immaturity of macrophage functions mainly comprises the age-dependent immaturity of protection against L. monocytogenes.

NZB mouse system for production of monoclonal antibodies to weak bacterial antigens: isolation of an IgG antibody to the polysaccharide capsules of Escherichia coli K1 and group B meningococci

A system for the production of monoclonal antibodies, particularly of the IgG type, against weakly immunogenic bacterial polysaccharide antigens is described. This system, which is based on the autoimmune NZB mouse strain, has been used to produce a monoclonal IgG2a antibody against the meningococcus group B and Escherichia coli K1 polysaccharides, identical homopolymers of alpha (2----8)-linked units of N-acetylneuraminic acid that are extremely poor immunogens. Comparison of the humoral immune responses of normal BALB/c mice and autoimmune NZB mice to hyperimmunization with group A, B, and C meningococci showed that, although both strains mounted a weak meningococcal B polysaccharide-specific IgM response, only the NZB strain mounted an IgG response. Similarly, NZB mice mounted a stronger IgG response to the more immunogenic group C meningococcal polysaccharide than did BALB/c mice, although this difference was less pronounced than that observed with meningococcal B polysaccharide. No difference between the two strains of mice was demonstrable with the strongly antigenic group A meningococcal polysaccharide. These results indicate that the NZB system may be generally useful for the production of monoclonal antibodies against weakly antigenic bacterial determinants.