Antibodies to the iron uptake ABC transporter lipoproteins PiaA and PiuA promote opsonophagocytosis of Streptococcus pneumoniae

Integrated structural proteomics and machine learning-guided mapping of a highly protective precision vaccine against mycoplasma pulmonis

Mycoplasma pulmonis (M. pulmonis) is an emerging respiratory infection commonly linked to prostate cancer, and it is classified under the group of mycoplasmas. Improved management of mycoplasma infections is essential due to the frequent ineffectiveness of current antibiotic treatments in completely eliminating these pathogens from the host. The objective of this study is to design and construct effective and protective vaccines guided by structural proteomics and machine learning algorithms to provide protection against the M. pulmonis infection. Through a thorough examination of the entire proteome of M. pulmonis, four specific targets Membrane protein P80, Lipoprotein, Uncharacterized protein and GGDEF domain-containing protein have been identified as appropriate for designing a vaccine. The proteins underwent mapping of cytotoxic T lymphocyte (CTL), helper T lymphocyte (HTL) (IFN)-γ ±, and B-cell epitopes using artificial and recurrent neural networks. The design involved the creation of mRNA and peptide-based vaccine, which consisted of 8 CTL epitopes associated by GGS linkers, 7 HTL (IFN-positive) epitopes, and 8 B-cell epitopes joined by GPGPG linkers. The vaccine designed exhibit antigenic behavior, non-allergenic qualities, and exceptional physicochemical attributes. Structural modeling revealed that correct folding is crucial for optimal functioning. The coupling of the MEVC and Toll-like Receptors (TLR)1, TLR2, and TLR6 was examined through molecular docking experiments. This was followed by molecular simulation investigations, which included binding free energy estimations. The results indicated that the dynamics of the interaction were stable, and the binding was strong. In silico cloning and optimization analysis revealed an optimized sequence with a GC content of 49.776 % and a CAI of 0.982. The immunological simulation results showed strong immune responses, with elevated levels of active and plasma B-cells, regulatory T-cells, HTL, and CTL in both IgM+IgG and secondary immune responses. The antigen was completely cleared by the 50th day. This study lays the foundation for creating a potent and secure vaccine candidate to combat the newly identified M. pulmonis infection in people.

Subtractive proteomics-guided vaccine targets identification and designing of multi-epitopes vaccine for immune response instigation against Burkholderia pseudomallei

In this study, a methodical workflow using subtractive proteomics, vaccine designing, molecular simulation, and agent-based modeling approaches were used to annotate the whole proteome of Burkholderia pseudomallei (strain K96243) for vaccine designing. Among the total 5717 proteins in the whole proteome, 505 were observed to be essential for the pathogen's survival and pathogenesis predicted by the Database of Essential Genes. Among these, 23 vaccine targets were identified, of which fimbrial assembly chaperone (Q63UH5), Outer membrane protein (Q63UH1), and Hemolysin-like protein (Q63UE4) were selected for the subsequent analysis based on the systematic approaches. Using immunoinformatic approaches CTL (cytotoxic T lymphocytes), HTL (helper T lymphocytes), IFN-positive, and B cell epitopes were predicted for these targets. A total of 9 CTL epitopes were added using the GSS linker, 6 HTL epitopes using the GPGPG linker, and 6 B cell epitopes using the KK linker. An adjuvant was added for enhanced antigenicity, an HIV-TAT peptide for improved delivery, and a PADRE sequence was added to form a 466 amino acids long vaccine construct. The construct was classified as non-allergenic, highly antigenic, and experimentally feasible. Molecular docking results validated the robust interaction of MEVC with immune receptors such as TLR2/4. Furthermore, molecular simulation revealed stable dynamics and compact nature of the complexes. The binding free energy results further validated the robust binding. In silico cloning, results revealed GC contents of 50.73 % and a CIA value of 0.978 which shows proper downstream processing. Immune simulation results reported that after the three injections of the vaccine a robust secondary immune response, improved antigen clearance, and effective immune memory generation were observed highlighting its potential for effective and sustained immunity. Future directions should encompass experimental validations, animal model studies, and clinical trials to substantiate the vaccine's efficacy, safety, and immunogenicity.

Design, development, and assessment of a novel multi-peptide vaccine targeting PspC, PsaA, and PhtD proteins of Streptococcus pneumoniae

Pneumococcus is the top cause of diseases such as pneumonia/meningitis, and of secondary infections after viral respiratory diseases like COVID-19/flu. Pneumococcal protein-based vaccines consisting of proteins with various functions in virulence might provide a qualified alternative for present vaccines. In this project, PspC, PsaA, and PhtD proteins were considered to anticipate B/T-cell epitopes using immunoinformatics to develop 4 multi-peptide constructs (C, A, and D individual constructs, and a fusion construct CAD). We tested whether vaccination with CAD is able to elicit more efficient protective responses against infection than vaccination with the individual constructs or combination of C + A + D. Based on the in silico results, the constructs were predicted to be antigenic, soluble, non-toxic, and stable, and also be able to provoke humoral/cellular immune reactions. When mice were immunized with the fusion protein, significantly higher levels of IgG and cytokines were induced in serum. The IgG in the fusion group had an effective bioactivity for pneumococcus clearance utilizing the complement pathway. The mice immunized with fusion protein were the most protected from challenge. This report for the first time presents a novel multi-peptide vaccine composed of immunodominant peptides of PspC, PsaA, and PhtD. In general, the experimental results supported the immunoinformatics predictions.

Immunoinformatics Prediction and Protective Efficacy of Vaccine Candidate PiuA-PlyD4 Against Streptococcus Pneumoniae

Purpose

This study was designed to evaluate the immune protective efficacy of the novel Streptococcus pneumoniae (S. pneumoniae) protein vaccine PiuA-PlyD4 through immunoinformatics prediction and in vitro and in vivo experiments.

Methods

In this study, we conducted immunoinformatics prediction and protection analysis on the fusion protein PiuA-PlyD4. The epitope composition of the vaccine was analyzed based on the prediction of B-cell and helper T-cell epitopes. Meanwhile, the molecular docking of PiuA and TLR2/4 was simulated. After immunizing C57BL/6 mice with the prepared vaccine, the biological safety, immunogenicity and conservation were evaluated. By constructing different infection models and from the aspects of adhesion inhibition and cytokines, the protective effect of the fusion protein vaccine PiuA-PlyD4 on S. pneumoniae infection was explored.

Results

PiuA-PlyD4 has abundant B-cell and helper T-cell epitopes and shows a high antigenicity score and structural stability. Molecular docking analysis suggested the potential interaction between PiuA and TLR2/4. The specific antibody titer of fusion protein antiserum was as high as (7.81±2.32) ×105. The protective effect of the immunized mice on nasal and lung colonization was significantly better than that of the control group, and the survival rate against S. pneumoniae infection of serotype 3 reached 50%. Cytokine detection showed that the humoral immune response, Th1, Th2 and Th17 cellular immune pathways were all involved in the process.

Conclusion

The study indicates that PiuA-PlyD4, whether the results are predicted by immunoinformatics or experimentally validated in vivo and in vitro, has good immunogenicity and immunoreactivity and can provide effective protection against S. pneumoniae infection. Therefore, it can be considered a promising prophylactic vaccine candidate for S. pneumoniae.

Recent progress in pneumococcal protein vaccines

Pneumococcal infections continue to pose a significant global health concern, necessitating the development of effective vaccines. Despite the progress shown by pneumococcal polysaccharide and conjugate vaccines, their limited coverage and the emergence of non-vaccine serotypes have highlighted the need for alternative approaches. Protein-based pneumococcal vaccines, targeting conserved surface proteins of Streptococcus pneumoniae, have emerged as a promising strategy. In this review, we provide an overview of the advancements made in the development of pneumococcal protein vaccines. We discuss the key protein vaccine candidates, highlight their vaccination results in animal studies, and explore the challenges and future directions in protein-based pneumococcal vaccine.

Pneumococcal capsule expression is controlled through a conserved, distal cis-regulatory element during infection

Streptococcus pneumoniae (the pneumococcus) is the major cause of bacterial pneumonia in the US and worldwide. Studies have shown that the differing chemical make-up between serotypes of its most important virulence factor, the capsule, can dictate disease severity. Here we demonstrate that control of capsule synthesis is also critical for infection and facilitated by two broadly conserved transcription factors, SpxR and CpsR, through a distal cis-regulatory element we name the 37-CE. Strikingly, changing only three nucleotides within this sequence is sufficient to render pneumococcus avirulent. Using in vivo and in vitro approaches, we present a model where SpxR interacts as a unique trimeric quaternary structure with the 37-CE to enable capsule repression in the airways. Considering its dramatic effect on infection, variation of the 37-CE between serotypes suggests this molecular switch could be a critical contributing factor to this pathogen's serotype-specific disease outcomes.

In silico designing of a novel epitope-based candidate vaccine against Streptococcus pneumoniae with introduction of a new domain of PepO as adjuvant

BACKGROUND

Streptococcus pneumoniae is the leading reason for invasive diseases including pneumonia and meningitis, and also secondary infections following viral respiratory diseases such as flu and COVID-19. Currently, serotype-dependent vaccines, which have several insufficiency and limitations, are the only way to prevent pneumococcal infections. Hence, it is plain to need an alternative effective strategy for prevention of this organism. Protein-based vaccine involving conserved pneumococcal protein antigens with different roles in virulence could provide an eligible alternative to existing vaccines.

METHODS

In this study, PspC, PhtD and PsaA antigens from pneumococcus were taken to account to predict B-cell and helper T-cell epitopes, and epitope-rich regions were chosen to build the construct. To enhance the immunogenicity of the epitope-based vaccine, a truncated N-terminal fragment of pneumococcal endopeptidase O (PepO) was used as a potential TLR2/4 agonist which was identified by molecular docking studies. The ultimate construct was consisted of the chosen epitope-rich regions, along with the adjuvant role (truncated N-PepO) and suitable linkers.

RESULTS

The epitope-based vaccine was assessed as regards physicochemical properties, allergenicity, antigenicity, and toxicity. The 3D structure of the engineered construct was modeled, refined, and validated. Molecular docking and simulation of molecular dynamics (MD) indicated the proper and stable interactions between the vaccine and TLR2/4 throughout the simulation periods.

CONCLUSIONS

For the first time this work presents a novel vaccine consisting of epitopes of PspC, PhtD, and PsaA antigens which is adjuvanted with a new truncated domain of PepO. The computational outcomes revealed that the suggested vaccine could be deemed an efficient therapeutic vaccine for S. pneumoniae; nevertheless, in vitro and in vivo examinations should be performed to prove the potency of the candidate vaccine.

SPD_0090 Negatively Contributes to Virulence of Streptococcus pneumoniae

In most bacteria, iron plays an important role in the survival of bacteria and the process of infection to the host. Streptococcus pneumoniae (S. pneumoniae) evolved three iron transporters (i.e., PiaABC, PiuABC, and PitABC) responsible for the transportation of three kinds of iron (i.e., ferrichrome, hemin, and ferric ion). Our previous study showed that both mRNA and protein levels of SPD_0090 were significantly upregulated in the ΔpiuA/ΔpiaA/ΔpitA triple mutant, but its detailed biological function is unknown. In this study, we constructed spd_0090 knockout and complement strain and found that the deletion of spd_0090 hinders bacterial growth. SPD_0090 is located on the cell membrane and affects the hemin utilization ability of S. pneumoniae. The cell infection model showed that the knockout strain had stronger invasion and adhesion ability. Notably, knockout of the spd_0090 gene resulted in an enhanced infection ability of S. pneumoniae in mice by increasing the expression of virulence factors. Furthermore, iTRAQ quantitative proteomics studies showed that the knockout of spd_0090 inhibited carbon metabolism and thus suppressed bacterial growth. Our study showed that SPD_0090 negatively regulates the virulence of S. pneumoniae.

Corrected and Republished from: "A Novel, Multiple-Antigen Pneumococcal Vaccine Protects against Lethal Streptococcus pneumoniae Challenge"

Current vaccination against Streptococcus pneumoniae uses vaccines based on capsular polysaccharides from selected serotypes and has led to nonvaccine serotype replacement disease. We have investigated an alternative serotype-independent approach, using multiple-antigen vaccines (MAV) prepared from S. pneumoniae TIGR4 lysates enriched for surface proteins by a chromatography step after culture under conditions that induce expression of heat shock proteins (Hsp; thought to be immune adjuvants). Proteomics and immunoblot analyses demonstrated that, compared to standard bacterial lysates, MAV was enriched with Hsps and contained several recognized protective protein antigens, including pneumococcal surface protein A (PspA) and pneumolysin (Ply). Vaccination of rodents with MAV induced robust antibody responses to multiple serotypes, including nonpneumococcal conjugate vaccine serotypes. Homologous and heterologous strains of S. pneumoniae were opsonized after incubation in sera from vaccinated rodents. In mouse models, active vaccination with MAV significantly protected against pneumonia, while passive transfer of rabbit serum from MAV-vaccinated rabbits significantly protected against sepsis caused by both homologous and heterologous S. pneumoniae strains. Direct comparison of MAV preparations made with or without the heat shock step showed no clear differences in protein antigen content and antigenicity, suggesting that the chromatography step rather than Hsp induction improved MAV antigenicity. Overall, these data suggest that the MAV approach may provide serotype-independent protection against S. pneumoniae.

Bacterial lipoproteins in sepsis

Bacterial lipoproteins are membrane proteins derived from both gram-negative and gram-positive bacteria. They seem to have diverse functions not only on bacterial growth, but also play an important role in host's virulence. Bacterial lipoproteins exert their action on host immune cells via TLR2/1 or TLR2/6. Therefore, bacterial lipoproteins also need to be considered while addressing bacterial pathogenicity besides classical bacterial endotoxin like LPS and other microbial associated molecular patterns such as LTA, and peptidoglycans. In this mini-review, we provide an overview of general bacterial lipoprotein biosynthesis and the need to understand the lipoprotein-mediated pathogenicity in diseases like sepsis.

HantavirusesDB: Vaccinomics and RNA-based therapeutics database for the potentially emerging human respiratory pandemic agents

Hantaviruses are etiological agents of several severe respiratory illnesses in humans and their human-to-human transmission has been reported. To cope with any potential pandemic, this group of viruses needs further research and a data platform. Therefore, herein we developed a database "HantavirusesDB (HVdb)", where genomics, proteomics, immune resource, RNAi based therapeutics and information on the 3D structures of druggable targets of the Orthohantaviruses are provided on a single platform. The database allows the researchers to effectively map the therapeutic strategies by designing multi-epitopes subunit vaccine and RNA based therapeutics. Moreover, the ease of the web interface allow the users to retrieve specific information from the database. Because of the high quality and excellent functionality of the HVdb, therapeutic research of Hantaviruses can be accelerated, and data analysis might be a foundation to design better treatment strategies targeting the hantaviruses. The database is accessible at http://hvdb.dqweilab-sjtu.com/index.php.

Immunogenomics guided design of immunomodulatory multi-epitope subunit vaccine against the SARS-CoV-2 new variants, and its validation through in silico cloning and immune simulation

Reports of the novel and more contagious strains of SARS-CoV-2 originating in different countries have further aggravated the pandemic situation. The recent substitutions in spike protein may be critical for the virus to evade the host's immune system and therapeutics that have already been developed. Thus, this study has employed an immunoinformatics pipeline to target the spike protein of this novel strain to construct an immunogenic epitope (CTL, HTL, and B cell) vaccine against the new variant. Our investigation revealed that 12 different epitopes imparted a critical role in immune response induction. This was validated by an exploration of physiochemical properties and experimental feasibility. In silico and host immune simulation confirmed the expression and induction of both primary and secondary immune factors such as IL, cytokines, and antibodies. The current study warrants further lab experiments to demonstrate its efficacy and safety.

Immunization with SP_1992 (DiiA) Protein of Streptococcus pneumoniae Reduces Nasopharyngeal Colonization and Protects against Invasive Disease in Mice

Knowledge-based vaccinology can reveal uncharacterized antigen candidates for a new generation of protein-based anti-pneumococcal vaccines. DiiA, encoded by the sp_1992 locus, is a surface protein containing either one or two repeats of a 37mer N-terminal motif that exhibits low interstrain variability. DiiA belongs to the core proteome, contains several conserved B-cell epitopes, and is associated with colonization and pathogenesis. Immunization with DiiA protein via the intraperitoneal route induced a strong IgG response, including different IgG subtypes. Vaccination with DiiA increased bacterial clearance and induced protection against sepsis, conferring 70% increased survival at 48 h post-infection when compared to the adjuvant control. The immunogenic response and survival rates in mice immunized with a truncated DiiA version lacking 119 N-terminal residues were remarkably lower, confirming the relevance of the repeat zone in the immunoprotection by DiiA. Intranasal immunization of mice with the entire recombinant protein elicited mucosal IgG and IgA responses that reduced bacterial colonization of the nasopharynx, confirming that this protein might be a vaccine candidate for reducing the carrier rate. DiiA constitutes an example of how functionally unannotated proteins may still represent promising candidates that can be used in prophylactic strategies against the pneumococcal carrier state and invasive disease.

Vaccination with LytA, LytC, or Pce of Streptococcus pneumoniae Protects against Sepsis by Inducing IgGs That Activate the Complement System

The emergence of non-vaccine serotypes of Streptococcus pneumoniae after the use of vaccines based in capsular polysaccharides demonstrates the need of a broader protection vaccine based in protein antigens and widely conserved. In this study, we characterized three important virulence factors of S. pneumoniae namely LytA, LytC, and Pce as vaccine candidates. These proteins are choline-binding proteins that belong to the cell wall hydrolases’ family. Immunization of mice with LytA, LytC, or Pce induced high titers of immunoglobulins G (IgGs) of different subclasses, with IgG1, IgG2a, and IgG2b as the predominant immunoglobulins raised. These antibodies activated the classical pathway of the complement system by increasing the recognition of C1q on the surface of pneumococcal strains of different serotypes. Consequently, the key complement component C3 recognized more efficiently these strains in the presence of specific antibodies elicited by these proteins, activating, therefore, the phagocytosis. Finally, a mouse sepsis model of infection was established, confirming that vaccination with these proteins controlled bacterial replication in the bloodstream, increasing the survival rate. Overall, these results demonstrate that LytA, LytC, and Pce can be protein antigens to be contained in a future universal vaccine against S. pneumoniae.

Rationally designed Human Cytomegalovirus gB nanoparticle vaccine with improved immunogenicity

Human cytomegalovirus (HCMV) is the primary viral cause of congenital birth defects and causes significant morbidity and mortality in immune-suppressed transplant recipients. Despite considerable efforts in vaccine development, HCMV infection still represents an unmet clinical need. In recent phase II trials, a MF59-adjuvanted gB vaccine showed only modest efficacy in preventing infection. These findings might be attributed to low level of antibodies (Abs) with a neutralizing activity induced by this vaccine. Here, we analyzed the immunogenicity of each gB antigenic domain (AD) and demonstrated that domain I of gB (AD5) is the main target of HCMV neutralizing antibodies. Furthermore, we designed, characterized and evaluated immunogenic responses to two different nanoparticles displaying a trimeric AD5 antigen. We showed that mice immunization with nanoparticles induces sera neutralization titers up to 100-fold higher compared to those obtained with the gB extracellular domain (gBECD). Collectively, these results illustrate with a medically relevant example the advantages of using a general approach combining antigen discovery, protein engineering and scaffold presentation for modern development of subunit vaccines against complex pathogens.

Genomic Characteristics of Invasive Streptococcus pneumoniae Serotype 1 in New Caledonia Prior to the Introduction of PCV13

Streptococcus pneumoniae serotype 1 is a common cause of global invasive pneumococcal disease. In New Caledonia, serotype 1 is the most prevalent serotype and led to two major outbreaks reported in the 2000s. The pneumococcal conjugate vaccine 13 (PCV13) was introduced into the vaccination routine, intending to prevent the expansion of serotype 1 in New Caledonia. Aiming to provide a baseline for monitoring the post-PCV13 changes, we performed a whole-genome sequence analysis on 67 serotype 1 isolates collected prior to the PCV13 introduction. To highlight the S. pneumoniae serotype 1 population structure, we performed a multilocus sequence typing (MLST) analysis revealing that NC serotype 1 consisted of 2 sequence types: ST3717 and the highly dominant ST306. Both sequence types harbored the same resistance genes to beta-lactams, macrolide, streptogramin B, fluoroquinolone, and lincosamide antibiotics. We have also identified 36 virulence genes that were ubiquitous to all the isolates. Among these virulence genes, the pneumolysin sequence presented an allelic profile associated with disease outbreaks and reduced hemolytic activity. Moreover, recombination hotspots were identified in 4 virulence genes and more notably in the cps locus (cps2L), potentially leading to capsular switching, a major mechanism of the emergence of nonvaccine types. In summary, this study represents the first overview of the genomic characteristics of S. pneumoniae serotype 1 in New Caledonia prior to the introduction of PCV13. This preliminary description represents a baseline to assess the impact of PCV13 on serotype 1 population structure and genomic diversity.

Identification and functional analysis of glutamine transporter in Streptococcus mutans

Background

Streptococcus mutans, a biofilm-forming bacterium, possesses several transporters that function as import/export molecules. Among them, the PII protein family is composed of members that regulate glutamine synthesis in bacterial species.

Objective

In this study, we characterized the function of the glutamine transporter in S. mutans MT8148.

Methods

The SMU.732 gene, corresponding to glnP in S. mutans, is homologous to the glutamine transporter gene in Bacillus subtilis. We constructed a glnP-inactivated mutant strain (GEMR) and a complement strain (comp-GEMR) and evaluated their biological functions.

Results

Growth of GEMR was similar in the presence and absence of glutamine, whereas the growth rates of MT8148 and comp-GEMR were significantly lower in the presence of glutamine as compared to its absence. Furthermore, biofilms formed by MT8148 and comp-GEMR were significantly thicker than that formed by GEMR, while the GEMR strain showed a significantly lower survival rate in an acidic environment than the other strains. Addition of n-phenyl-2-naphthylamine, used to label of the membrane, led to increased fluorescence intensity of MT8148 and GEMR, albeit that was significantly lower in the latter.

Conclusions

These results suggest that glnP is associated with glutamine transport in S. mutans, especially the import of glutamine involved in biofilm formation.

Pneumococcal Vaccines

Streptococcus pneumoniae is a Gram-Positive pathogen that is a major causative agent of pneumonia, otitis media, sepsis and meningitis across the world. The World Health Organization estimates that globally over 500,000 children are killed each year by this pathogen. Vaccines offer the best protection against S. pneumoniae infections. The current polysaccharide conjugate vaccines have been very effective in reducing rates of invasive pneumococcal disease caused by vaccine type strains. However, the effectiveness of these vaccines have been somewhat diminished by the increasing numbers of cases of invasive disease caused by non-vaccine type strains, a phenomenon known as serotype replacement. Since, there are currently at least 98 known serotypes of S. pneumoniae, it may become cumbersome and expensive to add many additional serotypes to the current 13-valent vaccine, to circumvent the effect of serotype replacement. Hence, alternative serotype independent strategies, such as vaccination with highly cross-reactive pneumococcal protein antigens, should continue to be investigated to address this problem. This chapter provides a comprehensive discussion of pneumococcal vaccines past and present, protein antigens that are currently under investigation as vaccine candidates, and other alternatives, such as the pneumococcal whole cell vaccine, that may be successful in reducing current rates of disease caused by S. pneumoniae.

Immune Response of BALB/c Mice toward Putative Calcium Transporter Recombinant Protein of Trichomonas vaginalis

Trichomoniasis is a common sexually transmitted infection caused by Trichomonas vaginalis, which actually does not exist a vaccine for control or prevention. Thus, the identification of new and potent immunogens in T. vaginalis, which can contribute to the development of a vaccine against this parasite, is necessary. Therefore, the aim of this work was to evaluate the potential of a recombinant Transient Receptor Potential-like channel of T. vaginalis (TvTRPV), as a promising immunogen in BALB/c mice. First, TvTRPV was cloned and expressed as a recombinant protein in Escherichia coli BL21 cells and purified by nickel affinity. Next, BALB/c mice were immunized and the antibody levels in mice serum and cytokines from the supernatant of macrophages and from co-culture systems were evaluated. Recombinant TvTRPV triggered high levels of specific total IgG in sera from the immunized mice. Also, a statistically significant increase of cytokines: IL-1β, IL-6, and TNF-α after stimulation with the corresponding antigens in vitro, was identified. Moreover, co-cultures using CD4⁺ T cells from immunized mice were able to identify higher levels of IL-10 and IFN-γ. These results were useful to validate the immunogenicity of TvTRPV in BALB/c mice, where IL-10-IFN-γ-secreting cells could play a role in infection control, supporting the potential of TvTRPV as a promising target for vaccine against T. vaginalis.

A Novel, Multiple-Antigen Pneumococcal Vaccine Protects against Lethal Streptococcus pneumoniae Challenge

Current vaccination against Streptococcus pneumoniae uses vaccines based on capsular polysaccharides from selected serotypes and has led to nonvaccine serotype replacement disease. We have investigated an alternative serotype-independent approach, using multiple-antigen vaccines (MAV) prepared from S. pneumoniae TIGR4 lysates enriched for surface proteins by a chromatography step after culture under conditions that induce expression of heat shock proteins (Hsp; thought to be immune adjuvants).

Current vaccination against Streptococcus pneumoniae uses vaccines based on capsular polysaccharides from selected serotypes and has led to nonvaccine serotype replacement disease. We have investigated an alternative serotype-independent approach, using multiple-antigen vaccines (MAV) prepared from S. pneumoniae TIGR4 lysates enriched for surface proteins by a chromatography step after culture under conditions that induce expression of heat shock proteins (Hsp; thought to be immune adjuvants). Proteomics and immunoblot analyses demonstrated that, compared to standard bacterial lysates, MAV was enriched with Hsps and contained several recognized protective protein antigens, including pneumococcal surface protein A (PspA) and pneumolysin (Ply). Vaccination of rodents with MAV induced robust antibody responses to multiple serotypes, including nonpneumococcal conjugate vaccine serotypes. Homologous and heterologous strains of S. pneumoniae were opsonized after incubation in sera from vaccinated rodents. In mouse models, active vaccination with MAV significantly protected against pneumonia, while passive transfer of rabbit serum from MAV-vaccinated rabbits significantly protected against sepsis caused by both homologous and heterologous S. pneumoniae strains. Direct comparison of MAV preparations made with or without the heat shock step showed no clear differences in protein antigen content and antigenicity, suggesting that the chromatography step rather than Hsp induction improved MAV antigenicity. Overall, these data suggest that the MAV approach may provide serotype-independent protection against S. pneumoniae.

Panproteome-wide analysis of antibody responses to whole cell pneumococcal vaccination

Pneumococcal whole cell vaccines (WCVs) could cost-effectively protect against a greater strain diversity than current capsule-based vaccines. Immunoglobulin G (IgG) responses to a WCV were characterised by applying longitudinally-sampled sera, available from 35 adult placebo-controlled phase I trial participants, to a panproteome microarray. Despite individuals maintaining distinctive antibody 'fingerprints', responses were consistent across vaccinated cohorts. Seventy-two functionally distinct proteins were associated with WCV-induced increases in IgG binding. These shared characteristics with naturally immunogenic proteins, being enriched for transporters and cell wall metabolism enzymes, likely unusually exposed on the unencapsulated WCV's surface. Vaccine-induced responses were specific to variants of the diverse PclA, PspC and ZmpB proteins, whereas PspA- and ZmpA-induced antibodies recognised a broader set of alleles. Temporal variation in IgG levels suggested a mixture of anamnestic and novel responses. These reproducible increases in IgG binding to a limited, but functionally diverse, set of conserved proteins indicate WCV could provide species-wide immunity.

Clinical trial registration: The trial was registered with ClinicalTrials.gov with Identifier NCT01537185; the results are available from https://clinicaltrials.gov/ct2/show/results/NCT01537185.

Intranasal Vaccination With Lipoproteins Confers Protection Against Pneumococcal Colonisation

Streptococcus pneumoniae is endowed with a variety of surface-exposed proteins representing putative vaccine candidates. Lipoproteins are covalently anchored to the cell membrane and highly conserved among pneumococcal serotypes. Here, we evaluated these lipoproteins for their immunogenicity and protective potential against pneumococcal colonisation. A multiplex-based immunoproteomics approach revealed the immunogenicity of selected lipoproteins. High antibody titres were measured in sera from mice immunised with the lipoproteins MetQ, PnrA, PsaA, and DacB. An analysis of convalescent patient sera confirmed the immunogenicity of these lipoproteins. Examining the surface localisation and accessibility of the lipoproteins using flow cytometry indicated that PnrA and DacB were highly abundant on the surface of the bacteria. Mice were immunised intranasally with PnrA, DacB, and MetQ using cholera toxin subunit B (CTB) as an adjuvant, followed by an intranasal challenge with S. pneumoniae D39. PnrA protected the mice from pneumococcal colonisation. For the immunisation with DacB and MetQ, a trend in reducing the bacterial load could be observed, although this effect was not statistically significant. The reduction in bacterial colonisation was correlated with the increased production of antigen-specific IL-17A in the nasal cavity. Immunisation induced high systemic IgG levels with a predominance for the IgG1 isotype, except for DacB, where IgG levels were substantially lower compared to MetQ and PnrA. Our results indicate that lipoproteins are interesting targets for future vaccine strategies as they are highly conserved, abundant, and immunogenic.

Sequencing of the variable region of rpsB to discriminate between Streptococcus pneumoniae and other streptococcal species

The vast majority of streptococci colonizing the human upper respiratory tract are commensals, only sporadically implicated in disease. Of these, the most pathogenic is Mitis group member, Streptococcus pneumoniae Phenotypic and genetic similarities between streptococci can cause difficulties in species identification. Using ribosomal S2-gene sequences extracted from whole-genome sequences published from 501 streptococci, we developed a method to identify streptococcal species. We validated this method on non-pneumococcal isolates cultured from cases of severe streptococcal disease (n = 101) and from carriage (n = 103), and on non-typeable pneumococci from asymptomatic individuals (n = 17) and on whole-genome sequences of 1157 pneumococcal isolates from meningitis in the Netherlands. Following this, we tested 221 streptococcal isolates in molecular assays originally assumed specific for S. pneumoniae, targeting cpsA, lytA, piaB, ply, Spn9802, zmpC and capsule-type-specific genes. Cluster analysis of S2-sequences showed grouping according to species in line with published phylogenies of streptococcal core genomes. S2-typing convincingly distinguished pneumococci from non-pneumococcal species (99.2% sensitivity, 100% specificity). Molecular assays targeting regions of lytA and piaB were 100% specific for S. pneumoniae, whereas assays targeting cpsA, ply, Spn9802, zmpC and selected serotype-specific assays (but not capsular sequence typing) showed a lack of specificity. False positive results were over-represented in species associated with carriage, although no particular confounding signal was unique for carriage isolates.

RitR is an archetype for a novel family of redox sensors in the streptococci that has evolved from two-component response regulators and is required for pneumococcal colonization

To survive diverse host environments, the human pathogen Streptococcus pneumoniae must prevent its self-produced, extremely high levels of peroxide from reacting with intracellular iron. However, the regulatory mechanism(s) by which the pneumococcus accomplishes this balance remains largely enigmatic, as this pathogen and other related streptococci lack all known redox-sensing transcription factors. Here we describe a two-component-derived response regulator, RitR, as the archetype for a novel family of redox sensors in a subset of streptococcal species. We show that RitR works to both repress iron transport and enable nasopharyngeal colonization through a mechanism that exploits a single cysteine (Cys128) redox switch located within its linker domain. Biochemical experiments and phylogenetics reveal that RitR has diverged from the canonical two-component virulence regulator CovR to instead dimerize and bind DNA only upon Cys128 oxidation in air-rich environments. Atomic structures show that Cys128 oxidation initiates a "helical unravelling" of the RitR linker region, suggesting a mechanism by which the DNA-binding domain is then released to interact with its cognate regulatory DNA. Expanded computational studies indicate this mechanism could be shared by many microbial species outside the streptococcus genus.

Flavin Reductase Contributes to Pneumococcal Virulence by Protecting from Oxidative Stress and Mediating Adhesion and Elicits Protection Against Pneumococcal Challenge

Pneumococcal flavin reductase (FlaR) is known to be cell-wall associated and possess age dependent antigenicity in children. This study aimed at characterizing FlaR and elucidating its involvement in pneumococcal physiology and virulence. Bioinformatic analysis of FlaR sequence identified three-conserved cysteine residues, suggesting a transition metal-binding capacity. Recombinant FlaR (rFlaR) bound Fe²⁺ and exhibited FAD-dependent NADP-reductase activity, which increased in the presence of cysteine or excess Fe²⁺ and inhibited by divalent-chelating agents. flaR mutant was highly susceptible to H₂O₂ compared to its wild type (WT) and complemented strains, suggesting a role for FlaR in pneumococcal oxidative stress resistance. Additionally, flaR mutant demonstrated significantly decreased mice mortality following intraperitoneal infection. Interestingly, lack of FlaR did not affect the extent of phagocytosis by primary mouse peritoneal macrophages but reduced adhesion to A549 cells compared to the WT and complemented strains. Noteworthy are the findings that immunization with rFlaR elicited protection in mice against intraperitoneal lethal challenge and anti-FlaR antisera neutralized bacterial virulence. Taken together, FlaR's roles in pneumococcal physiology and virulence, combined with its lack of significant homology to human proteins, point towards rFlaR as a vaccine candidate.

Diverse evolutionary patterns of pneumococcal antigens identified by pangenome-wide immunological screening

Characterizing the immune response to pneumococcal proteins is critical in understanding this bacterium's epidemiology and vaccinology. Probing a custom-designed proteome microarray with sera from 35 healthy US adults revealed a continuous distribution of IgG affinities for 2,190 potential antigens from the species-wide pangenome. Reproducibly elevated IgG binding was elicited by 208 "antibody binding targets" (ABTs), which included 109 variants of the diverse pneumococcal surface proteins A and C (PspA and PspC) and zinc metalloprotease A and B (ZmpA and ZmpB) proteins. Functional analysis found ABTs were enriched in motifs for secretion and cell surface association, with extensive representation of cell wall synthesis machinery, adhesins, transporter solute-binding proteins, and degradative enzymes. ABTs were associated with stronger evidence for evolving under positive selection, although this varied between functional categories, as did rates of diversification through recombination. Particularly rapid variation was observed at some immunogenic accessory loci, including a phage protein and a phase-variable glycosyltransferase ubiquitous among the diverse set of genomic islands encoding the serine-rich PsrP glycoprotein. Nevertheless, many antigens were conserved in the core genome, and strains' antigenic profiles were generally stable. No strong evidence was found for any epistasis between antigens driving population dynamics, or redundancy between functionally similar accessory ABTs, or age stratification of antigen profiles. These results highlight the paradox of why substantial variation is observed in only a subset of epitopes. This result may indicate only some interactions between immunoglobulins and ABTs clear pneumococcal colonization or that acquired immunity to pneumococci is an accumulation of individually weak responses to ABTs evolving under different levels of functional constraint.

Naturally Acquired Human Immunity to Pneumococcus Is Dependent on Antibody to Protein Antigens

Naturally acquired immunity against invasive pneumococcal disease (IPD) is thought to be dependent on anti-capsular antibody. However nasopharyngeal colonisation by Streptococcus pneumoniae also induces antibody to protein antigens that could be protective. We have used human intravenous immunoglobulin preparation (IVIG), representing natural IgG responses to S. pneumoniae, to identify the classes of antigens that are functionally relevant for immunity to IPD. IgG in IVIG recognised capsular antigen and multiple S. pneumoniae protein antigens, with highly conserved patterns between different geographical sources of pooled human IgG. Incubation of S. pneumoniae in IVIG resulted in IgG binding to the bacteria, formation of bacterial aggregates, and enhanced phagocytosis even for unencapsulated S. pneumoniae strains, demonstrating the capsule was unlikely to be the dominant protective antigen. IgG binding to S. pneumoniae incubated in IVIG was reduced after partial chemical or genetic removal of bacterial surface proteins, and increased against a Streptococcus mitis strain expressing the S. pneumoniae protein PspC. In contrast, depletion of type-specific capsular antibody from IVIG did not affect IgG binding, opsonophagocytosis, or protection by passive vaccination against IPD in murine models. These results demonstrate that naturally acquired protection against IPD largely depends on antibody to protein antigens rather than the capsule.

Immunization with LytB protein of Streptococcus pneumoniae activates complement-mediated phagocytosis and induces protection against pneumonia and sepsis

The cell wall glucosaminidase LytB of Streptococcus pneumoniae is a surface exposed protein involved in daughter cell separation, biofilm formation and contributes to different aspects of the pathogenesis process. In this study we have characterized the antibody responses after immunization of mice with LytB in the presence of alhydrogel as an adjuvant. Enzyme-linked immunosorbent assays measuring different subclasses of immunoglobulin G, demonstrated that the antibody responses to LytB were predominantly IgG1 and IgG2b, followed by IgG3 and IgG2a subclasses. Complement-mediated immunity against two different pneumococcal serotypes was investigated using sera from immunized mice. Immunization with LytB increased the recognition of S. pneumoniae by complement components C1q and C3b demonstrating that anti-LytB antibodies trigger activation of the classical pathway. Phagocytosis assays showed that serum containing antibodies to LytB stimulates neutrophil-mediated phagocytosis against S. pneumoniae. Animal models of infection including invasive pneumonia and sepsis were performed with two different clinical isolates. Vaccination with LytB increased bacterial clearance and induced protection demonstrating that LytB might be a good candidate to be considered in a future protein-based vaccine against S. pneumoniae.

Crucial residue Trp158 of lipoprotein PiaA stabilizes the ferrichrome-PiaA complex in Streptococcus pneumoniae

The pathogenic Streptococcus pneumoniae (S. pneumoniae) has evolved a special mechanism such as pneumococcal iron acquisition ATP binding cassette (PiaABC) to take up siderophore-iron from its host. The cell-surface lipoprotein PiaA, a key component of PiaABC, is the primary receptor to bind ferrichrome (Fc). To study the structure-function relationship of PiaA, three conservative amino-acid residues, Trp63, Trp158 and Phe255, in the hydrophobic barrel of the metal binding site of PiaA, were individually and collectively mutated to alanine; and the resulted single-point mutants, W63A, W158A and F255A, and triple mutant W63A/W158A/F255A were characterized by using biochemical and biophysical methods. Experiments showed that wild-type PiaA (WT-PiaA) and the single-point mutant proteins bound Fc with a similar kinetics mode, but the reaction rate of W158A was lower than that for WT-PiaA. The binding affinity of W158A toward Fc was significantly weaker than that of the WT-PiaA-Fc (wild-type PiaA bound with Fc) interaction. Furthermore, the absence of Trp158 in the protein led to a significant impact on the secondary structure of PiaA, resulting in a labile conformational structure of W158A, with impaired resistance to thermal and chemical denaturation. Collectively, Trp158 is a crucial residue for binding Fc, playing an important role in stabilizing the PiaA-Fc complex. This study revealed the critical role of the conserved tryptophan residues in Fc-binding protein PiaA, and provided valuable information for understanding the Fc transport mechanism mediated by PiaA or its homologous proteins in bacteria.

Conserved surface accessible nucleoside ABC transporter component SP0845 is essential for pneumococcal virulence and confers protection in vivo

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, sepsis and meningitis. Surface accessible proteins of S. pneumoniae are being explored for the development of a protein-based vaccine in order to overcome the limitations of existing polysaccharide-based pneumococcal vaccines. To identify a potential vaccine candidate, we resolved surface-associated proteins of S. pneumoniae TIGR4 strain using two-dimensional gel electrophoresis followed by immunoblotting with antisera generated against whole heat-killed TIGR4. Ten immunoreactive spots were identified by mass spectrometric analysis that included a putative lipoprotein SP0845. Analysis of the inferred amino acid sequence of sp0845 homologues from 36 pneumococcal strains indicated that SP0845 was highly conserved (>98% identity) and showed less than 11% identity with any human protein. Our bioinformatic and functional analyses demonstrated that SP0845 is the substrate-binding protein of an ATP-binding cassette (ABC) transporter that is involved in nucleoside uptake with cytidine, uridine, guanosine and inosine as the preferred substrates. Deletion of the gene encoding SP0845 renders pneumococci avirulent suggesting that it is essential for virulence. Immunoblot analysis suggested that SP0845 is expressed in in vitro grown pneumococci and during mice infection. Immunofluorescence microscopy and flow cytometry data indicated that SP0845 is surface exposed in encapsulated strains and accessible to antibodies. Subcutaneous immunization with recombinant SP0845 induced high titer antibodies in mice. Hyperimmune sera raised against SP0845 promoted killing of encapsulated pneumococcal strains in a blood bactericidal assay. Immunization with SP0845 protected mice from intraperitoneal challenge with heterologous pneumococcal serotypes. Based on its surface accessibility, role in virulence and ability to elicit protective immunity, we propose that SP0845 may be a potential candidate for a protein-based pneumococcal vaccine.

Exploitation of physiology and metabolomics to identify pneumococcal vaccine candidates

Streptococcus pneumoniae (the pneumococcus) is the etiologic agent of community-acquired pneumonia and invasive pneumococcal diseases such as septicemia and bacterial meningitis. The increasing antibiotic resistance and the suboptimal efficacy or limited serotype coverage of currently available vaccines urgently requires novel approaches in exploring new antimicrobials, therapeutic intervention strategies and vaccines. The current vaccine development strategies rely on the hypothesis that surface-exposed proteins, which are essential for pneumococcal virulence, are the most suitable candidates for future protein-based vaccines. Since virulence is closely linked with bacterial fitness, the potential of a pathogen to colonize and infect the host depends further on its physiology. This review summarizes the application of genome-wide techniques and their exploitation to decipher fundamental insights into bacterial factors associated with fitness, metabolism and virulence, leading to the discovery of vaccine candidates or antimicrobials.

The roles of transition metals in the physiology and pathogenesis of Streptococcus pneumoniae

For bacterial pathogens whose sole environmental reservoir is the human host, the acquisition of essential nutrients, particularly transition metals, is a critical aspect of survival due to tight sequestration and limitation strategies deployed to curtail pathogen outgrowth. As such, these bacteria have developed diverse, specialized acquisition mechanisms to obtain these metals from the niches of the body in which they reside. To oppose the spread of infection, the human host has evolved multiple mechanisms to counter bacterial invasion, including sequestering essential metals away from bacteria and exposing bacteria to lethal concentrations of metals. Hence, to maintain homeostasis within the host, pathogens must be able to acquire necessary metals from host proteins and to export such metals when concentrations become detrimental. Furthermore, this acquisition and efflux equilibrium must occur in a tissue-specific manner because the concentration of metals varies greatly within the various microenvironments of the human body. In this review, we examine the functional roles of the metal import and export systems of the Gram-positive pathogen Streptococcus pneumoniae in both signaling and pathogenesis.

Serotype-independent pneumococcal vaccines

Streptococcus pneumoniae remains an important cause of disease with high mortality and morbidity, especially in children and in the elderly. The widespread use of the polysaccharide conjugate vaccines in some countries has led to a significant decrease in invasive disease caused by vaccine serotypes, but an increase in disease caused by non-vaccine serotypes has impacted on the overall efficacy of these vaccines on pneumococcal disease. The obvious solution to overcome such shortcomings would be the development of new formulations that provide serotype-independent immunity. This review focuses on the most promising approaches, including protein antigens, whole cell pneumococcal vaccines, and recombinant bacteria expressing pneumococcal antigens. The protective capacity of these vaccine candidates against the different stages of pneumococcal infection, including colonization, mucosal disease, and invasive disease in animal models is reviewed. Some of the human trials that have already been performed or that are currently ongoing are presented. Finally, the feasibility and the possible shortcomings of these candidates in relation to an ideal vaccine against pneumococcal infections are discussed.

The effects of methionine acquisition and synthesis on Streptococcus pneumoniae growth and virulence

Bacterial pathogens need to acquire nutrients from the host, but for many nutrients their importance during infection remain poorly understood. We have investigated the importance of methionine acquisition and synthesis for Streptococcus pneumoniae growth and virulence using strains with gene deletions affecting a putative methionine ABC transporter lipoprotein (Sp_0149, metQ) and/or methionine biosynthesis enzymes (Sp_0585 - Sp_0586, metE and metF). Immunoblot analysis confirmed MetQ was a lipoprotein and present in all S. pneumoniae strains investigated. However, vaccination with MetQ did not prevent fatal S. pneumoniae infection in mice despite stimulating a strong specific IgG response. Tryptophan fluorescence spectroscopy and isothermal titration calorimetry demonstrated that MetQ has both a high affinity and specificity for L-methionine with a K_D of ∼25 nM, and a ΔmetQ strain had reduced uptake of C₁₄-methionine. Growth of the ΔmetQ/ΔmetEF strain was greatly impaired in chemically defined medium containing low concentrations of methionine and in blood but was partially restored by addition of high concentrations of exogenous methionine. Mixed infection models showed no attenuation of the ΔmetQ, ΔmetEF and ΔmetQ/ΔmetEF strains in their ability to colonise the mouse nasopharnyx. In a mouse model of systemic infection although significant infection was established in all mice, there were reduced spleen bacterial CFU after infection with the ΔmetQ/ΔmetEF strain compared to the wild-type strain. These data demonstrate that Sp_0149 encodes a high affinity methionine ABC transporter lipoprotein and that Sp_0585 – Sp_0586 are likely to be required for methionine synthesis. Although Sp_0149 and Sp_0585-Sp_0586 make a contribution towards full virulence, neither was essential for S. pneumoniae survival during infection.

Human pathogenic streptococcal proteomics and vaccine development

Gram-positive streptococci are non-motile, chain-forming bacteria commonly found in the normal oral and bowel flora of warm-blooded animals. Over the past decade, a proteomic approach combining 2-DE and MS has been used to systematically map the cellular, surface-associated and secreted proteins of human pathogenic streptococcal species. The public availability of complete streptococcal genomic sequences and the amalgamation of proteomic, genomic and bioinformatic technologies have recently facilitated the identification of novel streptococcal vaccine candidate antigens and therapeutic agents. The objective of this review is to examine the constituents of the streptococcal cell wall and secreted proteome, the mechanisms of transport of surface and secreted proteins, and describe the current methodologies employed for the identification of novel surface-displayed proteins and potential vaccine antigens.

Effects of deletion of the Streptococcus pneumoniae lipoprotein diacylglyceryl transferase gene lgt on ABC transporter function and on growth in vivo

Lipoproteins are an important class of surface associated proteins that have diverse roles and frequently are involved in the virulence of bacterial pathogens. As prolipoproteins are attached to the cell membrane by a single enzyme, prolipoprotein diacylglyceryl transferase (Lgt), deletion of the corresponding gene potentially allows the characterisation of the overall importance of lipoproteins for specific bacterial functions. We have used a Δlgt mutant strain of Streptococcus pneumoniae to investigate the effects of loss of lipoprotein attachment on cation acquisition, growth in media containing specific carbon sources, and virulence in different infection models. Immunoblots of triton X-114 extracts, flow cytometry and immuno-fluorescence microscopy confirmed the Δlgt mutant had markedly reduced lipoprotein expression on the cell surface. The Δlgt mutant had reduced growth in cation depleted medium, increased sensitivity to oxidative stress, reduced zinc uptake, and reduced intracellular levels of several cations. Doubling time of the Δlgt mutant was also increased slightly when grown in medium with glucose, raffinose and maltotriose as sole carbon sources. These multiple defects in cation and sugar ABC transporter function for the Δlgt mutant were associated with only slightly delayed growth in complete medium. However the Δlgt mutant had significantly reduced growth in blood or bronchoalveolar lavage fluid and a marked impairment in virulence in mouse models of nasopharyngeal colonisation, sepsis and pneumonia. These data suggest that for S. pneumoniae loss of surface localisation of lipoproteins has widespread effects on ABC transporter functions that collectively prevent the Δlgt mutant from establishing invasive infection.

Identification of genes that contribute to the pathogenesis of invasive pneumococcal disease by in vivo transcriptomic analysis

Streptococcus pneumoniae (the pneumococcus) continues to be responsible for a high level of global morbidity and mortality resulting from pneumonia, bacteremia, meningitis, and otitis media. Here we have used a novel technique involving niche-specific, genome-wide in vivo transcriptomic analyses to identify genes upregulated in distinct niches during pathogenesis after intranasal infection of mice with serotype 4 or 6A pneumococci. The analyses yielded 28 common, significantly upregulated genes in the lungs relative to those in the nasopharynx and 25 significantly upregulated genes in the blood relative to those in the lungs in both strains, some of which were previously unrecognized. The role of five upregulated genes from either the lungs or the blood in pneumococcal pathogenesis and virulence was then evaluated by targeted mutagenesis. One of the mutants (ΔmalX) was significantly attenuated for virulence in the lungs, two (ΔaliA and ΔilvH) were significantly attenuated for virulence in the blood relative to the wild type, and two others (ΔcbiO and ΔpiuA) were completely avirulent in a mouse intranasal challenge model. We also show that the products of aliA, malX, and piuA are promising candidates for incorporation into multicomponent protein-based pneumococcal vaccines currently under development. Importantly, we suggest that this new approach is a viable complement to existing strategies for the discovery of genes critical to the distinct stages of invasive pneumococcal disease and potentially has broad application for novel protein antigen discovery in other pathogens such as S. pyogenes, Haemophilus influenzae type b, and Neisseria meningitidis.

Infection with conditionally virulent Streptococcus pneumoniae Δpab strains induces antibody to conserved protein antigens but does not protect against systemic infection with heterologous strains

Avirulent strains of a bacterial pathogen could be useful tools for investigating immunological responses to infection and potentially effective vaccines. We have therefore constructed an auxotrophic TIGR4 Δpab strain of Streptococcus pneumoniae by deleting the pabB gene Sp_0665. The TIGR4 Δpab strain grew well in complete medium but was unable to grow in serum unless it was supplemented with para-aminobenzoic acid (PABA). The TIGR4 Δpab strain was markedly attenuated in virulence in mouse models of S. pneumoniae nasopharyngeal colonization, pneumonia, and sepsis. Supplementing mouse drinking water with PABA largely restored the virulence of TIGR4 Δpab. An additional Δpab strain constructed in the D39 capsular serotype 2 background was also avirulent in a sepsis model. Systemic inoculation of mice with TIGR4 Δpab induced antibody responses to S. pneumoniae protein antigens, including PpmA, PsaA, pneumolysin, and CbpD, but not capsular polysaccharide. Flow cytometry demonstrated that IgG in sera from TIGR4 Δpab-vaccinated mice bound to the surface of TIGR4 and D39 bacteria but not to a capsular serotype 3 strain, strain 0100993. Mice vaccinated with the TIGR4 Δpab or D39 Δpab strain by intraperitoneal inoculation were protected from developing septicemia when challenged with the homologous S. pneumoniae strain. Vaccination with the TIGR4 Δpab strain provided only weak or no protection against heterologous challenge with the D39 or 0100993 strain but did strongly protect against a TIGR4 capsular-switch strain expressing a serotype 2 capsule. The failure of cross-protection after systemic vaccination with Δpab bacteria suggests that parenteral administration of a live attenuated vaccine is not an attractive approach for preventing S. pneumoniae infection.

The factor H-binding fragment of PspC as a vaccine antigen for the induction of protective humoral immunity against experimental pneumococcal sepsis

Pneumococcal surface protein C (PspC) is a major virulence factor of Streptococcus pneumoniae and interferes with complement activity by binding complement factor H (fH). In this study, protection against experimental sepsis caused by pneumococci carrying different PspC variants was evaluated by immunisation with the fH-binding fragment of PspC. The mechanisms of protection mediated by antibodies to PspC were also studied. Mice were immunised with a PspC fragment (PspC(39-261)) from the type 3 strain HB565 and infected intravenously with either strain HB565 (homologous challenge), or strains D39 and TIGR4 (heterologous challenge). Immunisation with PspC(39-261) elicited high titers (>300,000) of PspC-specific serum IgG and conferred protection from challenge with HB565. In contrast, cross-protection was either limited or absent in vaccinated animals infected with D39 and TIGR4, respectively. To correlate protection with reactivity and function of PspC antibodies, pooled sera from vaccinated mice were tested in IgG binding and complement deposition experiments. IgG antibodies efficiently bound to HB565, while binding was lower with D39 and absent with TIGR4. In the presence of mouse post-immune sera, C3 deposition was increased onto HB565, while no effect was observed with D39 and TIGR4. Antibody cross-reactivity and complement deposition progressively declined with reduced amino acid identity between PspC variants. Antibodies to PspC were also found to interfere with fH binding to HB565. Finally, in vitro and ex vivo phagocytosis assays demonstrated that PspC-specific antibodies promoted opsonophagocytic killing of bacteria.

Impact of glutamine transporters on pneumococcal fitness under infection-related conditions

The genomic analysis of Streptococcus pneumoniae predicted six putative glutamine uptake systems, which are expressed under in vitro conditions, as shown here by reverse transcription-PCR. Four of these operons consist of glnHPQ, while two lack glnH, which encodes a soluble glutamine-binding protein. Here, we studied the impact of two of these glutamine ATP-binding cassette transporters on S. pneumoniae D39 virulence and phagocytosis, which consist of GlnQ and a translationally fused protein of GlnH and GlnP. Mice infected intranasally with D39Δgln0411/0412 showed significantly increased survival times and a significant delay in the development of pneumococcal pneumonia compared to those infected with D39, as observed in real time using bioluminescent pneumococci. In a mouse sepsis model, the mutant D39Δgln0411/0412 showed only moderate but significant attenuation. In contrast, the D39Δgln1098/1099 knockout strain was massively attenuated in the pneumonia and septicemia mouse infection model. To cause pneumonia or sepsis with D39Δgln1098/1099, infection doses 100- to 10,000-fold higher than those used for wild-type strain D39 were required. In an experimental mouse meningitis model, D39Δgln1098/1099 produced decreased levels of white blood cells in cerebrospinal fluid and showed decreased numbers of bacteria in the bloodstream compared to D39 and D39Δgln0411/0412. Phagocytosis experiments revealed significantly decreased intracellular survival rates of mutants D39Δgln1098/1099 and D39Δgln0411/0412 compared to wild-type D39, suggesting that the deficiency of Gln uptake systems impairs resistance to oxidative stress. Taken together, our results demonstrate that both glutamine uptake systems are required for full virulence of pneumococci but exhibit different impacts on the pathogenesis of pneumococci under in vivo conditions.

Lipoproteins of bacterial pathogens

Bacterial lipoproteins are a set of membrane proteins with many different functions. Due to this broad-ranging functionality, these proteins have a considerable significance in many phenomena, from cellular physiology through cell division and virulence. Here we give a general overview of lipoprotein biogenesis and highlight examples of the roles of lipoproteins in bacterial disease caused by a selection of medically relevant Gram-negative and Gram-positive pathogens: Mycobacterium tuberculosis, Streptococcus pneumoniae, Borrelia burgdorferi, and Neisseria meningitidis. Lipoproteins have been shown to play key roles in adhesion to host cells, modulation of inflammatory processes, and translocation of virulence factors into host cells. As such, a number of lipoproteins have been shown to be potential vaccines. This review provides a summary of some of the reported roles of lipoproteins and of how this knowledge has been exploited in some cases for the generation of novel countermeasures to bacterial diseases.

Priming innate immune responses to infection by cyclooxygenase inhibition kills antibiotic-susceptible and -resistant bacteria

Inhibition of cyclooxygenase (COX)-derived prostaglandins (PGs) by nonsteroidal anti-inflammatory drugs (NSAIDs) mediates leukocyte killing of bacteria. However, the relative contribution of COX1 versus COX2 to this process, as well as the mechanisms controlling it in mouse and humans, are unknown. Indeed, the potential of NSAIDs to facilitate leukocyte killing of drug-resistant bacteria warrants investigation. Therefore, we carried out a series of experiments in mice and humans, finding that COX1 is the predominant isoform active in PG synthesis during infection and that its prophylactic or therapeutic inhibition primes leukocytes to kill bacteria by increasing phagocytic uptake and reactive oxygen intermediate-mediated killing in a cyclic adenosine monophosphate (cAMP)-dependent manner. Moreover, NSAIDs enhance bacterial killing in humans, exerting an additive effect when used in combination with antibiotics. Finally, NSAIDs, through the inhibition of COX prime the innate immune system to mediate bacterial clearance of penicillin-resistant Streptococcus pneumoniae serotype 19A, a well-recognized vaccine escape serotype of particular concern given its increasing prevalence and multi-antibiotic resistance. Therefore, these data underline the importance of lipid mediators in host responses to infection and the potential of inhibitors of PG signaling pathways as adjunctive therapies, particularly in the con-text of antibiotic resistance.