Vaccines against bacterial meningitis

Underestimated Subsequent Sensorineural Hearing Loss after Septicemia

Background and Objectives: Hearing loss after septicemia has been found in mice; the long-term risk increased 50-fold in young adults in a previous study. Hearing loss after septicemia has not received much attention. The aim of this study was to assess the relationship between septicemia and subsequent hearing loss. Materials and Methods: Inpatient data were obtained from the Taiwan Insurance Database. We defined patients with sensorineural hearing loss and excluded patients under 18 years of age. Patients without hearing loss were selected as controls at a frequency of 1:5. The date of admission was defined as the date of diagnosis. Comorbidities in the 3 years preceding the date of diagnosis were retrieved retrospectively. Associations with hearing loss were established by multiple logistic regression and forward stepwise selection. Results: The odds ratio (OR) for the association between sepsis and hearing loss was 3.052 (95% CI: 1.583-5.884). Autoimmune disease (OR: 5.828 (95% CI: 1.906-17.816)), brain injury (OR: 2.264 (95% CI: 1.212-4.229)) and ischemic stroke (OR: 1.47 (95% CI: 1.087-1.988)) were associated with hearing loss. Conclusions: Our study shows that hearing loss occurred after septicemia. Apoptosis caused by sepsis and ischemia can lead to hair cell damage, leading to hearing loss. Clinicians should be aware of possible subsequent complications of septicemia and provide appropriate treatment and prevention strategies for complications.

Immunobiology of Carbohydrates: Implications for Novel Vaccine and Adjuvant Design Against Infectious Diseases

Carbohydrates are ubiquitous molecules expressed on the surface of nearly all living cells, and their interaction with carbohydrate-binding proteins is critical to many immunobiological processes. Carbohydrates are utilized as antigens in many licensed vaccines against bacterial pathogens. More recently, they have also been considered as adjuvants. Interestingly, unlike other types of vaccines, adjuvants have improved immune response to carbohydrate-based vaccine in humans only in a few cases. Furthermore, despite the discovery of many new adjuvants in the last years, aluminum salts, when needed, remain the only authorized adjuvant for carbohydrate-based vaccines. In this review, we highlight historical and recent advances on the use of glycans either as vaccine antigens or adjuvants, and we review the use of currently available adjuvants to improve the efficacy of carbohydrate-based vaccines. A better understanding of the mechanism of carbohydrate interaction with innate and adaptive immune cells will benefit the design of a new generation of glycan-based vaccines and of immunomodulators to fight both longstanding and emerging diseases.

Vaccines to Prevent Meningitis: Historical Perspectives and Future Directions

Despite advances in the development and introduction of vaccines against the major bacterial causes of meningitis, the disease and its long-term after-effects remain a problem globally. The Global Roadmap to Defeat Meningitis by 2030 aims to accelerate progress through visionary and strategic goals that place a major emphasis on preventing meningitis via vaccination. Global vaccination against Haemophilus influenzae type B (Hib) is the most advanced, such that successful and low-cost combination vaccines incorporating Hib are broadly available. More affordable pneumococcal conjugate vaccines are becoming increasingly available, although countries ineligible for donor support still face access challenges and global serotype coverage is incomplete with existing licensed vaccines. Meningococcal disease control in Africa has progressed with the successful deployment of a low-cost serogroup A conjugate vaccine, but other serogroups still cause outbreaks in regions of the world where broadly protective and affordable vaccines have not been introduced into routine immunization programs. Progress has lagged for prevention of neonatal meningitis and although maternal vaccination against the leading cause, group B streptococcus (GBS), has progressed into clinical trials, no GBS vaccine has thus far reached Phase 3 evaluation. This article examines current and future efforts to control meningitis through vaccination.

Perspective of a Pediatrician: Shared Pathogenesis of the Three Most Successful Pathogens of Children

Highly successful invasive pathogens exploit host vulnerabilities by adapting tools to co-opt highly conserved host features. This is especially true when pathogens develop ligands to hijack trafficking routes or signaling patterns of host receptors. In this context, highly successful pathogens can be grouped together by the patterns of organs infected and diseases they cause. In the case of this perspective, the focus is on the historically most successful invasive bacterial pathogens of children that cause pneumonia, sepsis and meningitis: Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. This triad shares a ligand to bind to PAF receptor to enter host cells despite early defenses by innate immunity. All three also target laminin receptor to cross endothelial barriers using a common set of molecular tools that may prove to be a design for a cross-protective vaccine.

A stabilized glycomimetic conjugate vaccine inducing protective antibodies against Neisseria meningitidis serogroup A

Neisseria meningitidis serogroup A capsular polysaccharide (MenA CPS) consists of (1 → 6)-2-acetamido-2-deoxy-α-D-mannopyranosyl phosphate repeating units, O-acetylated at position C3 or C4. Glycomimetics appear attractive to overcome the CPS intrinsic lability in physiological media, due to cleavage of the phosphodiester bridge, and to develop a stable vaccine with longer shelf life in liquid formulation. Here, we generate a series of non-acetylated carbaMenA oligomers which are proven more stable than the CPS. An octamer (DP8) inhibits the binding of a MenA specific bactericidal mAb and polyclonal serum to the CPS, and is selected for further in vivo testing. However, its CRM197 conjugate raises murine antibodies towards the non-acetylated CPS backbone, but not the natural acetylated form. Accordingly, random O-acetylation of the DP8 is performed, resulting in a structure (Ac-carbaMenA) showing improved inhibition of anti-MenA CPS antibody binding and, after conjugation to CRM197, eliciting anti-MenA protective murine antibodies, comparably to the vaccine benchmark.

Hearing impairment in young and middle-aged septicemia survivors

The ability of sepsis to induce acute phase hearing impairment has been evaluated in septic and sepsis-surviving mice. The relationship between septicemia and long-term hearing impairment remains unknown in humans.The data were obtained from the Taiwan Longitudinal National Health Insurance Database from 2000 to 2013. We identified patients suffering from septicemia after discharge, excluding those younger than 18 years old and older than 65 years old. The comparison group was matched based on age, sex, and comorbidities. The outcome was hearing impairment occurring after septicemia. The risk factors associated with hearing impairment were established using multivariate Cox proportional hazard regression.Our study found that septicemia associated with hearing impairment had an adjusted hazard ratio (HR) of 53.11 (95% confidence interval [CI]: 41.74-67.59). The other factors related to hearing impairment in young and middle-aged septicemia survivors included male sex (adjusted HR 1.31 [95% CI: 1.14-1.5]), chronic kidney disease (adjusted HR 1.63 [95% CI: 1.38-1.94]), and otoscleroisis (adjusted HR 231.54 [95% CI: 31.61-1695.8]).Our study revealed that septicemia was associated with increased development of hearing impairment in young and middle-aged humans in the long term. Clinicians should be aware of long-term septicemia-related hearing impairment and provide prevention strategies for otopathy in septicemia survivors.

Epitope Mapping of a Monoclonal Antibody Directed against Neisserial Heparin Binding Antigen Using Next Generation Sequencing of Antigen-Specific Libraries

We explore here the potential of a newly described technology, which is named PROFILER and is based on next generation sequencing of gene-specific lambda phage-displayed libraries, to rapidly and accurately map monoclonal antibody (mAb) epitopes. For this purpose, we used a novel mAb (designated 31E10/E7) directed against Neisserial Heparin-Binding Antigen (NHBA), a component of the anti-group B meningococcus Bexsero® vaccine. An NHBA phage-displayed library was affinity-selected with mAb 31E10/E7, followed by massive sequencing of the inserts present in antibody-selected phage pools. Insert analysis identified an amino acid stretch (D91-A128) in the N-terminal domain, which was shared by all of the mAb-enriched fragments. Moreover, a recombinant fragment encompassing this sequence could recapitulate the immunoreactivity of the entire NHBA molecule against mAb 31E10/E7. These results were confirmed using a panel of overlapping recombinant fragments derived from the NHBA vaccine variant and a set of chemically synthetized peptides covering the 10 most frequent antigenic variants. Furthermore, hydrogen-deuterium exchange mass-spectrometry analysis of the NHBA-mAb 31E10/E7 complex was also compatible with mapping of the epitope to the D91-A128 region. Collectively, these results indicate that the PROFILER technology can reliably identify epitope-containing antigenic fragments and requires considerably less work, time and reagents than other epitope mapping methods.

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10(2) μM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10(2) μM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro.

Major Advances in the Development of Synthetic Oligosaccharide-Based Vaccines

Because of their involvement in a variety of different biological processes and their occurrence onto pathogens and malignant cell surface, carbohydrates have been identified as ideal candidates for vaccine formulation. However, as free oligosaccharides are poorly immunogenic and do not induce immunological memory in the most at risk population (infants and young children, elderly and immunocompromised patients), glycoconjugate vaccines containing the same carbohydrate antigen covalently linked to an immunogenic carrier protein have gained a prominent role. Accordingly, a number of glycoconjugate vaccines mostly directed against infections caused by bacterial pathogens have been licensed and are currently available on the market. However, also glycoconjugate vaccines suffer from significant drawbacks. The challenging procedures required for the isolation and purification of the carbohydrate antigen from its natural source often lead to poor homogeneity and presence of biological contaminants, resulting in batch-to-batch variability. Moreover, in some cases, the overwhelming immunogenicity of the carrier protein may induce the carbohydrate epitope suppression, causing hyporesponsiveness. The development of synthetic oligosaccharide-based vaccine candidates, characterized by the presence of pure and well-defined synthetic oligosaccharide structures, is expected to meet the requirement of homogeneous and highly reproducible preparations.

In the present chapter, we report on the major advances in the development of synthetic carbohydrate-based vaccines. First of all, we describe different strategies developed during the last years to circumvent the inherent difficulties of classical oligosaccharide synthesis, such as the one-pot glycosylation and the solid-phase synthesis, and their application to the preparation of carbohydrate antigens apt to conjugation with protein carriers. Next, we discuss the most representative methodologies employed for the chemical ligation of oligosaccharide structures to proteins. Finally, in the last section, we report significant examples of fully synthetic vaccines exploiting the multivalency effect. These constructs are based on the concept that the conjugation of multiple copies of synthetic oligosaccharide antigens to multivalent scaffolds, such as dendrimers, (cyclo)peptides, gold nanoparticles, and calixarenes, raises cooperative interactions between carbohydrates and immune receptors, leading to strong enhancement of the saccharide antigen immunogenicity.

Neisseria meningitidis B vaccines: recent advances and possible immunization policies

Since the development of the first-generation vaccines based on outer membrane vesicles (OMV), which were able to contain strain-specific epidemics, but were not suitable for universal use, enormous steps forward in the prevention of Neisseria meningitidis B have been made. The first multicomponent vaccine, Bexsero(®), has recently been authorized for use; other vaccines, bivalent rLP2086 and next-generation OMV vaccines, are under development. The new vaccines may substantially contribute to reducing invasive bacterial infections as they could cover most Neisseria meningitidis B strains. Moreover, other potentially effective serogroup B vaccine candidates are being studied in preclinical settings. It is therefore appropriate to review what has recently been achieved in the prevention of disease caused by serogroup B.

Current concepts in the treatment of bacterial meningitis beyond the neonatal period

The epidemiology and treatment approach to bacterial meningitis has changed dramatically since the advent of antimicrobial therapy. New vaccines against meningeal pathogens have been implemented into national immunization programs successfully around the world. Antibiotic resistance has had a considerable impact on the efficacy of several therapeutic agents. In this review, the authors will discuss the principles of antibiotic chemotherapy, focusing on new agents for the treatment of penicillin-resistant pneumococci and adjunctive treatments to reduce the inflammatory response to bacterial infection of the meninges.

Immunoactivity of protein conjugates of carba analogues from Neisseria meningitidis a capsular polysaccharide

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that is a major cause of epidemic meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of a liquid glycoconjugate vaccine against MenA are hampered by the poor hydrolytic stability of its capsular polysaccharide (CPS), consisting of (1→6)-linked 2-acetamido-2-deoxy-α-d-mannopyranosyl phosphate repeating units. The replacement of the ring oxygen with a methylene group to generate a carbocyclic analogue leads to enhancement of its chemical stability. Herein, we report conjugation of carbocyclic analogue monomer, dimer, and trimer to the protein carrier CRM197. After immunization in mice, only the conjugated trimer was able to induce specific anti-MenA polysaccharide IgG antibodies with in vitro bactericidal activity, although to a lesser extent than pentadecamer and hexamer oligomers obtained from mild acid hydrolysis of the native polysaccharide conjugated to the same protein carrier. This study represents the first proof-of-concept that hydrolytically stable structural analogues of saccharide antigens can be used for the development of efficacious antimicrobial preventative therapies. Conjugates with longer carbocyclic oligomers and/or precise acetylation patterns could further increase the induced immune response to a level comparable with those of commercially available anti-meningococcal glycoconjugate vaccines.

Computational approaches to identify common subunit vaccine candidates against bacterial meningitis

Bacterial meningitis, an infection of the membranes (meninges) and cerebrospinal fluid (CSF) surrounding the brain and spinal cord, is a major cause of death and disability all over the world. From perinatal period to adult, four common organisms responsible for most of the bacterial meningitis are Streptococcus pneumonia, Neisseria meningitidis, Haemophilus influenza and Staphylococcus aureus. As the disease is caused by more organisms, currently available vaccines for bacterial meningitis are specific and restricted to some of the serogroups or serotypes of each bacterium. In an effort to design common vaccine against bacterial meningitis, proteomes of the four pathogens were compared to extract seven common surface exposed ABC transporter proteins. Pro-Pred server was used to investigate the seven surface exposed proteins for promiscuous T-cell epitopes prediction. Predicted 22 T-cell epitopes were validated through published positive control, SYFPEITHI and immune epitope database to reduce the epitope dataset into seven. T-cell epitope 162-FMILPIFNV-170 of spermidine/putrescine ABC transporter permease (potH) protein was conserved across the four selected pathogens of bacterial meningitis. Hence, structural analysis was extended for epitope 162-FMILPIFNV-170. Crystal structures of HLA-DRB alleles were retrieved and structure of potH was modeled using Prime v3.0 for structural analysis. Computational docking of HLA-DRB alleles and epitope 162-FMILPIFNV-170 of potH was performed using Glide v5.7. RMSD and RMSF of simulation studies were analyzed by Desmond v3.2. The docking and simulation results revealed that the HLA-DRB-epitope complex was stable with interaction repressive function of HLA. Thus, the epitope would be ideal candidate for T-cell driven subunit vaccine design against bacterial meningitis.

Effects of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D-conjugate vaccine on nasopharyngeal bacterial colonization in young children: a randomized controlled trial

This study evaluated effects of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D-conjugate vaccine (PHiDCV) compared with the 7-valent vaccine on nasopharyngeal bacterial colonization, specifically nontypeable Haemophilus influenzae (NTHi). PHiD-CV had no differential effect on nasopharyngeal NTHi colonization.

Background. This study evaluated the effects of the 10-valent pneumococcal nontypeable Haemophilus influenzae protein D–conjugate vaccine (PHiD-CV) on nasopharyngeal bacterial colonization compared with the 7-valent pneumococcal conjugate vaccine (7vCRM) in young children.

Methods. A randomized controlled trial in the Netherlands, initiated 2 years after 7vCRM introduction, was conducted between 1 April 2008 and 1 December 2010. Infants (N = 780) received either PHiD-CV or 7vCRM (2:1) at 2, 3, 4, and 11–13 months of age. Nasopharyngeal samples taken at 5, 11, 14, 18, and 24 months of age were cultured to detect Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and Staphylococcus aureus. Polymerase chain reaction assays quantified H. influenzae and S. pneumoniae and confirmed H. influenzae as nontypeable (NTHi). Primary outcome measure was vaccine efficacy (VE) against NTHi colonization.

Results. In both groups, NTHi colonization increased with age from 33% in 5-month-olds to 65% in 24-month-olds. Three months postbooster, VE against colonization was 0.5% (95% confidence interval [CI], −21.8% to 18.4%) and VE against acquisition 10.9% (95% CI, −31.3% to 38.9%). At each sampling moment, no differences between groups in either NTHi prevalence or H. influenzae density were detected. Streptococcus pneumoniae (range, 39%–57%), M. catarrhalis (range, 63%­–69%), and S. aureus (range, 9%–30%) colonization patterns were similar between groups.

Conclusions. PHiD-CV had no differential effect on nasopharyngeal NTHi colonization or H. influenzae density in healthy Dutch children up to 2 years of age, implying that herd effects for NTHi are not to be expected. Other bacterial colonization patterns were also similar.

Clinical Trials Registration NCT00652951.

Association of meningococcal phenotypes and genotypes with clinical characteristics and mortality of meningitis in children

BACKGROUND

Neisseria meningitidis meningitis represents approximately one-half of the meningococcal cases in French children. To explore the contribution of bacterial typing in improving the management of cases, we aimed to describe clinical characteristics and mortality of meningococcal meningitis in children reported to the multicenter survey system, GPIP/ACTIV, in association with phenotypes/genotypes of bacterial isolates.

METHODS

From 2001 to 2005, 259 pediatric wards and 168 microbiology laboratories enrolled all children with bacterial meningitis. Risk factors, vaccination status, signs and symptoms, cerebrospinal fluid analysis, treatments and case fatality rate were recorded.

RESULTS

A total of 962 cases of Neisseria meningitidis meningitis among a total of 2131 bacterial meningitis (45%) were recorded (mean age, 4.5 +/- 4.7 years). Serogroup distribution of the isolates was 62.3%, 33.7%, 2.9%, 0.6%, and 0.6% for serogroups B, C, W135, A and Y, respectively. The major clonal complexes were ST-41/44 (32.2%), ST-11 (21.9%), ST-32 (20.8%), ST-8 (8.2%), and ST-269 (4.9%). Despite global heterogeneity of the isolates, 2 phenotypes/genotypes were of interest. Isolates of the phenotype/genotype B:14:P1.7,16/ST-32 (56% clustered in the region of Haute Normandie) were observed in older children (8.6 years) and were associated with a higher case fatality rate (12%) than were other phenotypes of serogroup B. The phenotype/genotype C:2a:P1.5/ST-11 was found in 26.3% of serogroup C cases and was possibly associated with a higher mortality among serogroup C (9.9% for C and 5.9% for B, P = 0.04).

CONCLUSIONS

This large survey provides data that could be important for implementation of future vaccines. Typing of meningococcal isolates could contribute to an understanding of prognosis in meningococcal meningitis.

Changing epidemiology of bacterial meningitis

Immunization against the most common meningeal pathogens is the leading factor associated with decreased incidence of bacterial meningitis in countries where routine vaccination is available. This is most dramatically illustrated by the reduction in the incidence of Haemophilus influenzae type b meningitis. The incidence of bacterial meningitis has decreased by 55% since the introduction of the H. influenzae type b conjugate vaccine in 1990. H. influenzae occurred primarily in children younger than 5 years of age, and so the median age of patients with bacterial meningitis has now increased to 39 years of age in the United States, and the leading pathogen is currently Streptococcus pneumoniae. Three other control measures (ie, universal screening and antibiotic prophylaxis of pregnant women for Group B streptococci and the implementation and availability of the S. pneumoniae and Neisseria meningitidis conjugate vaccines) have likely further decreased the incidence of these meningeal pathogens. Lastly, the worldwide emergence of multidrug-resistant pneumococci has complicated the empiric therapy of bacterial meningitis.

Characterization of fHbp, nhba (gna2132), nadA, porA, sequence type (ST), and genomic presence of IS1301 in group B meningococcal ST269 clonal complex isolates from England and Wales

Highly effective glycoconjugate vaccines exist against four of the five major pathogenic groups of meningococci: A, C, W-135, and Y. An equivalent vaccine against group B meningococci (menB) has remained elusive due to the poorly immunogenic capsular polysaccharide. A promising alternative, the investigational recombinant menB (rMenB)- outer membrane vesicle (OMV) vaccine, contains fHBP, NHBA (previously GNA2132), NadA, and outer membrane vesicles (OMVs) from the New Zealand MeNZB vaccine. MenB currently accounts for 90% of meningococcal disease in England and Wales, where the multilocus sequence type (ST) 269 (ST269) clonal complex (cc269) has recently expanded to account for a third of menB cases. To assess the potential cc269 coverage of the rMenB-OMV vaccine, English and Welsh cc269 isolates from the past decade were genetically characterized with respect to fHBP, NHBA, and NadA. All of the isolates harbored fHbp and nhba alleles, while 98% of the cc269 isolates were devoid of nadA. Subvariant profiling of fHbp, nhba, and porA against STs revealed the presence of two broadly distinct and well-defined clusters of isolates, centered around ST269 and ST275, respectively. An additional molecular marker, insertion sequence IS1301, was found to be present in 100% and <2% of isolates of the respective clusters. On the basis of the genetic data, the potential rMenB-OMV coverage of cc269 in England and Wales is high (up to 100%) within both clusters. Expression studies and serum bactericidal antibody assays will serve to enhance predictions of coverage and will augment ongoing studies regarding the significance of IS1301 within the ST269 cluster.

[Characteristics of meningococcal meningitis in children in France]

BACKGROUND

In France, meningococcal meningitis account for 50% of bacterial meningitis in children. The GPIP/ACTIV (Groupe de Pathologie Infectieuse Pédiatrique and Association Clinique et Thérapeutique Infantile du Val de Marne) set up an active surveillance network to analyze the epidemiological, clinical and biological features of meningococcal meningitis.

METHODS

From 2001 to 2007, 252 French paediatric wards working with 166 microbiology laboratories enrolled all children (0-18 years old) with bacterial meningitis. Risk factors, signs and symptoms, vaccination status, cerebrospinal fluid analysis, treatments and case fatality rate were recorded.

RESULTS

During the period of the study, 1344 meningococcal meningitis were reported among 2951 (45.5%) bacterial meningitis. Mean age was 4.4 years (+/-4.7, median 2.5) and 2/3 cases occurred in children under 5 years (68.5%). Serogroup B (59.1%) was preponderant following by serogroup C (28.9%). 25% of children had received an antibiotic treatment 24hours before lumbar puncture. A shock was reported in 31.3% of cases. Cerebrospinal fluid culture was positive in 73% of cases. All N. meningitidis isolates were susceptible to cefotaxime and ceftriaxone while 41.6% and 25.7% showed reduced susceptibility to penicillin and amoxicillin respectively. Two cases of meningitis due to isolates of serogroups C and B were reported in two children that were respectively vaccinated using A+C plain saccharide vaccine or two doses of MenBvac vaccine. All patients had received beta-lactamin. Global case fatality rate was 6.6% but was higher (9.9%) for serogroup C than for serogroup B (5.5%) (p=0,007).

CONCLUSION

This study is among the largest series of microbiologically documented meningococcal meningitis to date (more than 1300 cases). In France, meningococal is responsible for 50 % of meningitis. Effective meningococcal serogroup B vaccine and serogroup C vaccination recommendation could lessen considerably the burden of meningococal meningitis.

Synthesis and biological evaluation of phosphono analogues of capsular polysaccharide fragments from Neisseria meningitidis A

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that may cause explosive epidemics of meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against Neisseria meningitidis A is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, which is made up of (1-->6)-linked 2-acetamido-2-deoxy-alpha-D-mannopyranosyl phosphate repeating units. Since this chemical lability is a product of the inherent instability of the phosphodiester bridges, here we report the synthesis of phosphonoester-linked oligomers of N-acetyl mannosamine as candidates for stabilised analogues of the corresponding phosphate-bridged saccharides. The installation of each interglycosidic phosphonoester linkage was achieved by Mitsunobu coupling of a glycosyl C-phosphonate building block with the 6-OH moiety of a mannosaminyl residue. Each of the synthesised compounds contains an O-linked aminopropyl spacer at its reducing end (alpha- or beta-oriented) to allow for protein conjugation. The relative affinities of the synthetic molecules were investigated by a competitive ELISA assay and showed that a human polyclonal anti-MenA serum can recognise both the phosphonoester-bridged fragments 1-3 and their monomeric subunits, glycosides 20 and 21. Moreover, the biological results suggest that the abilities of these compounds to inhibit the binding of a specific antibody to MenA polysaccharide are dependent on the chain lengths of the molecules, but independent on the orientations of the anomeric linkers.

Is persistent bacterial infection good for your health?

Certain bacterial pathogens have evolved to survive in their human hosts for long periods without causing harm. Is it possible that these persistent bacterial infections provide a protective benefit to the host?