Mucosal immunization with polyamine transport protein D (PotD) protects mice against nasopharyngeal colonization with Streptococcus pneumoniae

Converso T. Role of the polyamine transporter PotABCD during biofilm formation by Streptococcus pneumoniae

Streptococcus pneumoniae is a bacterium of great global importance, responsible for more than one million deaths per year. This bacterium is commonly acquired in the first years of life and colonizes the upper respiratory tract asymptomatically by forming biofilms that persist for extended times in the nasopharynx. However, under conditions that alter the bacterial environment, such as viral infections, pneumococci can escape from the biofilm and invade other niches, causing local and systemic disease of varying severity. The polyamine transporter PotABCD is required for optimal survival of the organism in the host. Immunization of mice with recombinant PotD can reduce subsequent bacterial colonization. PotD has also been suggested to be involved in pneumococcal biofilm development. Therefore, in this study we aimed to elucidate the role of PotABCD and polyamines in pneumococcal biofilm formation. First, the formation of biofilms was evaluated in the presence of exogenous polyamines-the substrate transported by PotABCD-added to culture medium. Next, a potABCD-negative strain was used to determine biofilm formation in different model systems using diverse levels of complexity from abiotic surface to cell substrate to in vivo animal models and was compared with its wild-type strain. The results showed that adding more polyamines to the medium stimulated biofilm formation, suggesting a direct correlation between polyamines and biofilm formation. Also, deletion of potABCD operon impaired biofilm formation in all models tested. Interestingly, more differences between wild-type and mutant strains were observed in the more complex model, which emphasizes the significance of employing more physiological models in studying biofilm formation.

Immune response induced in mice by a hybrid rPotD-PdT pneumococcal protein

Streptococcus pneumoniae is a human pathogen that colonizes the naso and/or oropharynx and can cause otitis, pneumonia, bacteremia and meningitis. To broaden the protection against pneumococcus, several pneumococcal proteins have been investigated as vaccine candidates. In this study we analyzed the immunological response induced by mouse subcutaneous immunization with a fusion of the Polyamine transport protein D (PotD) and a pneumolysin derivative (PdT), resulting in a hybrid rPotD-PdT protein. Immunization of mice with rPotD-PdT induced increased production of nitric oxide, indicating a higher innate immune response. In agreement, immunization of mice with the hybrid protein was more immunogenic than the individual proteins or their combination, eliciting higher antibody levels. The anti-rPotD-PdT IgG displayed increased binding onto the pneumococcal surface. Furthermore, the anti-rPotD-PdT antisera promoted superior opsonophagocytosis as compared with the other tested formulations. However, despite that the encouraging results in vitro, immunization with the hybrid was not sufficient to induce protection against sepsis with a highly virulent pneumococcal strain. taken together, the results suggest that hybrid proteins are an interesting strategy, able to promote improved immune responses, but the inclusion of other antigens may be necessary to promote protection against invasive infections caused by this bacterium.

The Effect of Impaired Polyamine Transport on Pneumococcal Transcriptome

Infections due to Streptococcus pneumoniae, a commensal in the nasopharynx, still claim a significant number of lives worldwide. Genome plasticity, antibiotic resistance, and limited serotype coverage of the available polysaccharide-based conjugate vaccines confounds therapeutic interventions to limit the spread of this pathogen. Pathogenic mechanisms that allow successful adaption and persistence in the host could be potential innovative therapeutic targets. Polyamines are ubiquitous polycationic molecules that regulate many cellular processes. We previously reported that deletion of polyamine transport operon potABCD, which encodes a putrescine/spermidine transporter (ΔpotABCD), resulted in an unencapsulated attenuated phenotype. Here, we characterize the transcriptome, metabolome, and stress responses of polyamine transport-deficient S. pneumoniae. Compared with the wild-type strain, the expression of genes involved in oxidative stress responses and the nucleotide sugar metabolism was reduced, while expression of genes involved in the Leloir, tagatose, and pentose phosphate pathways was higher in ΔpotABCD. A metabolic shift towards the pentose phosphate pathway will limit the synthesis of precursors of capsule polysaccharides. Metabolomics results show reduced levels of glutathione and pyruvate in the mutant. Our results also show that the potABCD operon protects pneumococci against hydrogen peroxide and nitrosative stress. Our findings demonstrate the importance of polyamine transport in pneumococcal physiology that could impact in vivo fitness. Thus, polyamine transport in pneumococci represents a novel target for therapeutic interventions.

The expansive effects of polyamines on the metabolism and virulence of Streptococcus pneumoniae

Polyamines are common intracellular metabolites of nearly all cells, and their conservation across a vast diversity of cells suggests critical roles for these compounds in cellular physiology. Most intracellular polyamines are associated with RNA and, subsequently, polyamines have significant effects on transcription and translation. Putrescine and spermidine are the most common polyamines in bacteria. Intracellular polyamine pools in bacteria are tightly controlled by both de novo synthesis and transport. Polyamine homeostasis is emerging as a critical parameter of multiple pathways and physiology with substantial impact on bacterial pathogenesis, including the important human pathogen Streptococcus pneumoniae. Modulation of polyamine metabolism in pneumococci is an important regulator of central metabolism. It has broad effects on virulence factors such as capsule as well as stress responses that ultimately impact the survival of pneumococcus in a host. Polyamine transport protein as a single antigen or in combination with other pneumococcal proteins is shown to be an efficacious immunogen that protects against nasopharyngeal colonization, and invasive disease. A comprehensive description of polyamine metabolic pathways and their intersection with pneumococcal pathogenesis will undoubtedly point to novel approaches for treatment and prevention of pneumococcal disease.

SP_0916 Is an Arginine Decarboxylase That Catalyzes the Synthesis of Agmatine, Which Is Critical for Capsule Biosynthesis in Streptococcus pneumoniae

The global burden of invasive pneumococcal diseases, including pneumonia and sepsis, caused by Streptococcus pneumoniae, a Gram-positive bacterial pathogen, remains a major global health risk. The success of pneumococcus as a pathogen can be attributed to its ability to regulate the synthesis of capsular polysaccharide (CPS) during invasive disease. We previously reported that deletion of a putative lysine decarboxylase (LDC; ΔSP_0916) in pneumococcal serotype 4 (TIGR4) results in reduced CPS. SP_0916 locus is annotated as either an arginine or a LDC in pneumococcal genomes. In this study, by biochemical characterization of the recombinant SP_0916, we determined the substrate specificity of SP_0916 and show that it is an arginine decarboxylase (speA/ADC). We also show that deletion of the polyamine transporter (potABCD) predicted to import putrescine and spermidine results in reduced CPS, while deletion of spermidine synthase (speE) for the conversion of putrescine to spermidine had no impact on the capsule. Targeted metabolomics identified a correlation between reduced levels of agmatine and loss of capsule in ΔspeA and ΔpotABCD, while agmatine levels were comparable between the encapsulated TIGR4 and ΔspeE. Exogenous supplementation of agmatine restored CPS in both ΔpotABCD and ΔspeA. These results demonstrate that agmatine is critical for regulating the CPS, a predominant virulence factor in pneumococci.

The long search for a serotype independent pneumococcal vaccine

Introduction: Serotype replacement - a consequence of polysaccharide vaccine use - will continue to drive the inclusion of new serotypes on conjugate vaccines, increasing production complexity and costs, and making an already expensive vaccine less accessible to developing countries, where prevalence is higher and resources available for health systems, scarcer. Serotype-independent formulations are a promising option, but so far they have not been successful in reducing colonization/transmission.Areas covered: Protein-based and whole-cell vaccine candidates studied in the past 30 years. Challenges for serotype-independent vaccine development and alternative approaches.Expert opinion: Clinical trials performed so far demonstrated the importance to establish more reliable animal models and better correlates of protection. Defining appropriate endpoints for clinical trials of serotype-independent vaccine candidates has been a challenge. Inhibition of colonization has been evaluated, but concern on the extent of bacterial elimination is still a matter of debate. Challenges on establishing representative sites for clinical trials, sample sizes and appropriate age groups are discussed. On a whole, although many challenges will have to be overcome, establishing protein-based antigens as serotype-independent vaccines is still the best alternative against the huge burden of pneumococcal diseases in the world.

Polyamine Transport Protein PotD Protects Mice against Haemophilus parasuis and Elevates the Secretion of Pro-Inflammatory Cytokines of Macrophage via JNK-MAPK and NF-κB Signal Pathways through TLR4

The potD gene, belonging to the well-conserved ABC (ATP-binding cassette) transport system potABCD, encodes the bacterial substrate-binding subunit of the polyamine transport system. In this study, we found PotD in Haemophilus (Glaesserella) parasuis could actively stimulate both humoral immune and cellular immune responses and elevate lymphocyte proliferation, thus eliciting a Th1-type immune response in a murine immunity and infection model. Stimulation of Raw 264.7 macrophages with PotD validated that Toll-like receptor 4, rather than 2, participated in the positive transcription and expression of pro-inflammatory cytokines IL–1β, IL–6, and TNF–α using qPCR and ELISA. Blocking signal-regulated JNK–MAPK and RelA(p65) pathways significantly decreased PotD-induced pro-inflammatory cytokine production. Overall, we conclude that vaccination of PotD could induce both humoral and cellular immune responses and provide immunoprotection against H. parasuis challenge. The data also suggest that Glaesserella PotD is a novel pro-inflammatory mediator and induces TLR4-dependent pro-inflammatory activity in Raw 264.7 macrophages through JNK–MAPK and RelA(p65) pathways.

Polyamine Synthesis Effects Capsule Expression by Reduction of Precursors in Streptococcus pneumoniae

Streptococcus pneumoniae (pneumococcus, Spn) colonizes the human nasopharynx asymptomatically but can cause infections such as otitis media, and invasive pneumococcal disease such as community-acquired pneumonia, meningitis, and sepsis. Although the success of Spn as a pathogen can be attributed to its ability to synthesize and regulate capsular polysaccharide (CPS) for survival in the host, the mechanisms of CPS regulation are not well-described. Recent studies from our lab demonstrate that deletion of a putative polyamine biosynthesis gene (ΔcadA) in Spn TIGR4 results in the loss of the capsule. In this study, we characterized the transcriptome and metabolome of ΔcadA and identified specific mechanisms that could explain the regulatory role of polyamines in pneumococcal CPS biosynthesis. Our data indicate that impaired polyamine synthesis impacts galactose to glucose interconversion via the Leloir pathway which limits the availability of UDP-galactose, a precursor of serotype 4 CPS, and UDP-N-acetylglucosamine (UDP-GlcNAc), a nucleotide sugar precursor that is at the intersection of CPS and peptidoglycan repeat unit biosynthesis. Reduced carbon flux through glycolysis, coupled with altered fate of glycolytic intermediates further supports impaired synthesis of UDP-GlcNAc. A significant increase in the expression of transketolases indicates a potential shift in carbon flow toward the pentose phosphate pathway (PPP). Higher PPP activity could constitute oxidative stress responses in ΔcadA which warrants further investigation. The results from this study clearly demonstrate the potential of polyamine synthesis, targeted for cancer therapy in human medicine, for the development of novel prophylactic and therapeutic strategies for treating bacterial infections.

Complete Genome Sequence of Streptococcus pneumoniae Serotype 19F Strain EF3030

We report the complete genome sequence of Streptococcus pneumoniae EF3030, a serotype 19F isolate that colonizes the nasopharynx of mice while being mostly noninvasive. Such attributes make this strain highly attractive in pneumococcal carriage studies.

We report the complete genome sequence of Streptococcus pneumoniae EF3030, a serotype 19F isolate that colonizes the nasopharynx of mice while being mostly noninvasive. Such attributes make this strain highly attractive in pneumococcal carriage studies. The availability of its complete genomic sequence is likely to advance studies in the field.

Draft Genome Sequence of Pediatric Otitis Media Isolate Streptococcus pneumoniae Strain EF3030, Which Forms In Vitro Biofilms That Closely Mimic In Vivo Biofilms

Here, we report the draft genome sequence of Streptococcus pneumoniae EF3030, a pediatric otitis media isolate active in biofilm assays of epithelial colonization. The final draft assembly included 2,209,198 bp; the annotation predicted 2,120 coding DNA sequences (CDSs), 4 complete rRNA operons, 58 tRNAs, 3 noncoding RNAs (ncRNAs), and 199 pseudogenes.

Here, we report the draft genome sequence of Streptococcus pneumoniae EF3030, a pediatric otitis media isolate active in biofilm assays of epithelial colonization. The final draft assembly included 2,209,198 bp; the annotation predicted 2,120 coding DNA sequences (CDSs), 4 complete rRNA operons, 58 tRNAs, 3 noncoding RNAs (ncRNAs), and 199 pseudogenes.

Identification of SP1683 as a pneumococcal protein that is protective against nasopharyngeal colonization

Serotype-independent protein-based pneumococcal vaccines represent attractive alternatives to capsular polysaccharide-based vaccines. The aim of this study was to identify novel immunogenic proteins from Streptococcus pneumoniae that may be used in protein-based pneumococcal vaccine. An immunoproteomics approach and a humanized severe combined immunodeficient mouse model were used to identify S. pneumoniae proteins that are immunogenic for the human immune system. Among the several proteins identified, SP1683 was selected, recombinantly produced, and infection and colonization murine models were used to evaluate the capacity of SP1683 to elicit protective responses, in comparison to known pneumococcal immunogenic proteins (PhtD and detoxified pneumolysin, dPly). Immunisation with SP1683 elicited a weaker antibody response than immunisation with PhtD and did not provide protection in the model of invasive disease. However, similar to PhtD, it was able to significantly reduce colonization in the mouse model of nasopharyngeal carriage. Treatment with anti-IL17A and anti-IL17F antibodies abolished the protection against colonization elicited by SP1683 or PhtD + dPly, which indicated that the protection afforded in this model was Th17-dependent. In conclusion, intranasal immunization with the pneumococcal protein SP1683 conferred IL17-dependent protection against nasopharyngeal carriage in mice, but systemic immunization did not protect against invasive disease. These results do not support the use of SP1683 as an isolated pneumococcal vaccine antigen. Nevertheless, SP1683 could be used as a first line of defence in formulations combining several proteins.

The Role of Cadaverine Synthesis on Pneumococcal Capsule and Protein Expression

Invasive infections caused by Streptococcus pneumoniae, a commensal in the nasopharynx, pose significant risk to human health. Limited serotype coverage by the available polysaccharide-based conjugate vaccines coupled with increasing incidence of antibiotic resistance complicates therapeutic strategies. Bacterial physiology and metabolism that allows pathogens to adapt to the host are a promising avenue for the discovery of novel therapeutics. Intracellular polyamine concentrations are tightly regulated by biosynthesis, transport and degradation. We previously reported that deletion of cadA, a gene that encodes for lysine decarboxylase, an enzyme that catalyzes cadaverine synthesis results in an attenuated phenotype. Here, we report the impact of cadA deletion on pneumococcal capsule and protein expression. Our data show that genes for polyamine biosynthesis and transport are downregulated in ∆cadA. Immunoblot assays show reduced capsule in ∆cadA. Reduced capsule synthesis could be due to reduced transcription and availability of precursors for synthesis. The capsule is the predominant virulence factor in pneumococci and is critical for evading opsonophagocytosis and its loss in ∆cadA could explain the reported attenuation in vivo. Results from this study show that capsule synthesis in pneumococci is regulated by polyamine metabolism, which can be targeted for developing novel therapies.

Polyamine transporter potABCD is required for virulence of encapsulated but not nonencapsulated Streptococcus pneumoniae

Streptococcus pneumoniae is commonly found in the human nasopharynx and is the causative agent of multiple diseases. Since invasive pneumococcal infections are associated with encapsulated pneumococci, the capsular polysaccharide is the target of licensed pneumococcal vaccines. However, there is an increasing distribution of non-vaccine serotypes, as well as nonencapsulated S. pneumoniae (NESp). Both encapsulated and nonencapsulated pneumococci possess the polyamine oligo-transport operon (potABCD). Previous research has shown inactivation of the pot operon in encapsulated pneumococci alters protein expression and leads to a significant reduction in pneumococcal murine colonization, but the role of the pot operon in NESp is unknown. Here, we demonstrate deletion of potD from the NESp NCC1 strain MNZ67 does impact expression of the key proteins pneumolysin and PspK, but it does not inhibit murine colonization. Additionally, we show the absence of potD significantly increases biofilm production, both in vitro and in vivo. In a chinchilla model of otitis media (OM), the absence of potD does not significantly affect MNZ67 virulence, but it does significantly reduce the pathogenesis of the virulent encapsulated strain TIGR4 (serotype 4). Deletion of potD also significantly reduced persistence of TIGR4 in the lungs but increased persistence of PIP01 in the lungs. We conclude the pot operon is important for the regulation of protein expression and biofilm formation in both encapsulated and NCC1 nonencapsulated Streptococcus pneumoniae. However, in contrast to encapsulated pneumococcal strains, polyamine acquisition via the pot operon is not required for MNZ67 murine colonization, persistence in the lungs, or full virulence in a model of OM. Therefore, NESp virulence regulation needs to be further established to identify potential NESp therapeutic targets.

MetQ of Neisseria gonorrhoeae Is a Surface-Expressed Antigen That Elicits Bactericidal and Functional Blocking Antibodies

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection (STI) gonorrhea, is a growing public health threat for which a vaccine is urgently needed. We characterized the functional role of the gonococcal MetQ protein, which is the methionine binding component of an ABC transporter system, and assessed its potential as a candidate antigen for inclusion in a gonococcal vaccine. MetQ has been found to be highly conserved in all strains investigated to date, it is localized on the bacterial surface, and it binds l-methionine with a high affinity. MetQ is also involved in gonococcal adherence to cervical epithelial cells. Mutants lacking MetQ have impaired survival in human monocytes, macrophages, and serum. Furthermore, antibodies raised against MetQ are bactericidal and are able to block gonococcal adherence to epithelial cells. These data suggest that MetQ elicits both bactericidal and functional blocking antibodies and is a valid candidate antigen for additional investigation and possible inclusion in a vaccine for prevention of gonorrhea.

Role of antibodies and IL17-mediated immunity in protection against pneumococcal otitis media

Widespread vaccination against Streptococcus pneumoniae (the pneumococcus) has significantly reduced pneumococcal disease caused by vaccine serotypes. Despite vaccination, overall pneumococcal colonization rates in children have not reduced and otitis media (OM) by non-vaccine serotypes remains one of the most common childhood infections. Pneumococcal surface protein A (PspA) has been shown to be a promising protein antigen to induce broad protection against pneumococcal colonization. However, its ability to protect against OM remains unclear. Using our previously established mouse model of influenza-virus induced pneumococcal OM, we here show that intranasal vaccination of mice with PspA together with the mucosal adjuvant CTB results in a decrease in pneumococcal load in the middle ears. This decrease correlated with the induction of PspA-specific IgA, a balanced IgG1:IgG2a antibody response and the induction of a mucosal Th17 response. Our data suggests that the IL-17 response to PspA is more important for protection against OM, whilst the presence of antibodies may be less important, as determined in mice deficient in IL-17 signaling or antibody production. Together, these results suggest that mucosal vaccination with PspA may not only protect against colonization, but also against the development of virus-induced pneumococcal OM.

Pneumococcal DnaJ modulates dendritic cell-mediated Th1 and Th17 immune responses through Toll-like receptor 4 signaling pathway

Pneumococcal DnaJ was recently shown to be a potential protein vaccine antigen that induces strong Th1 and Th17 immune response against streptococcus pneumoniae infection in mice. However, how DnaJ mediates T cell immune response against S. pneumoniae infection has not been addressed. Here, we investigate whether DnaJ contributes to the development of T cell immunity through the activation of bone marrow-derived dendritic cells (BMDCs). We found that endotoxin-free recombinant DnaJ (rDnaJ) induced activation and maturation of BMDCs via recognition of Toll-like receptor 4 (TLR4) and activation of MAPKs, NF-κB and PI3K-Akt pathways. rDnaJ-treated BMDCs effectively stimulated naïve CD4⁺ T cells to secrete IFN-γ and IL-17A. Splenocytes from mice that were adoptively transferred with rDnaJ-pulsed BMDCs secreted higher levels of IFN-γ and IL-17A compared with those that received PBS-activated BMDCs. Splenocytes from TLR4^-/- mice immunized with rDnaJ produced lower levels of IFN-γ and IL-17A compared with those from wild type mice. Our findings indicate that DnaJ can induce Th1 and Th17 immune responses against S. pneumoniae through activation of BMDCs in a TLR4-dependent manner.

Streptococcus pneumoniae biofilm formation and dispersion during colonization and disease

Streptococcus pneumoniae (the pneumococcus) is a common colonizer of the human nasopharynx. Despite a low rate of invasive disease, the high prevalence of colonization results in millions of infections and over one million deaths per year, mostly in individuals under the age of 5 and the elderly. Colonizing pneumococci form well-organized biofilm communities in the nasopharyngeal environment, but the specific role of biofilms and their interaction with the host during colonization and disease is not yet clear. Pneumococci in biofilms are highly resistant to antimicrobial agents and this phenotype can be recapitulated when pneumococci are grown on respiratory epithelial cells under conditions found in the nasopharyngeal environment. Pneumococcal biofilms display lower levels of virulence in vivo and provide an optimal environment for increased genetic exchange both in vitro and in vivo, with increased natural transformation seen during co-colonization with multiple strains. Biofilms have also been detected on mucosal surfaces during pneumonia and middle ear infection, although the role of these biofilms in the disease process is debated. Recent studies have shown that changes in the nasopharyngeal environment caused by concomitant virus infection, changes in the microflora, inflammation, or other host assaults trigger active release of pneumococci from biofilms. These dispersed bacteria have distinct phenotypic properties and transcriptional profiles different from both biofilm and broth-grown, planktonic bacteria, resulting in a significantly increased virulence in vivo. In this review we discuss the properties of pneumococcal biofilms, the role of biofilm formation during pneumococcal colonization, including their propensity for increased ability to exchange genetic material, as well as mechanisms involved in transition from asymptomatic biofilm colonization to dissemination and disease of otherwise sterile sites. Greater understanding of pneumococcal biofilm formation and dispersion will elucidate novel avenues to interfere with the spread of antibiotic resistance and vaccine escape, as well as novel strategies to target the mechanisms involved in induction of pneumococcal disease.

Panel 6: Vaccines

OBJECTIVE

To update progress on the effectiveness of vaccine for prevention of acute otitis media (AOM) and identification of promising candidate antigens against Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and Moraxella catarrhalis.

REVIEW METHODS

Literature searches were performed in OvidSP and PubMed restricted to articles published between June 2007 and September 2011. Search terms included otitis media, vaccines, vaccine antigens, and each of the otitis pathogens and candidate antigens identified in the ninth conference report.

CONCLUSIONS

The current report provides further evidence for the effectiveness of pneumococcal conjugate vaccines (PCVs) in the prevention of otitis media. Observational studies demonstrate a greater decline in AOM episodes than reported in clinical efficacy trials. Unmet challenges include extending protection to additional serotypes and additional pathogens, the need to prevent early episodes, the development of correlates of protection for protein antigens, and the need to define where an otitis media vaccine strategy fits with priorities for child health.

IMPLICATIONS FOR PRACTICE

Acute otitis media continues to be a burden on children and families, especially those who suffer from frequent recurrences. The 7-valent PCV (PCV7) has reduced the burden of disease as well as shifted the pneumococcal serotypes and the distribution of otopathogens currently reported in children with AOM. Antibiotic resistance remains an ongoing challenge. Multiple candidate antigens have demonstrated the necessary requirements of conservation, surface exposure, immunogenicity, and protection in animal models. Further research on the role of each antigen in pathogenesis, in the development of correlates of protection in animal models, and in new adjuvants to elicit responses in the youngest infants is likely to be productive and permit more antigens to move into human clinical trials.

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.

Pneumococcal interactions with epithelial cells are crucial for optimal biofilm formation and colonization in vitro and in vivo

The human nasopharynx is the main reservoir for Streptococcus pneumoniae (the pneumococcus) and the source for both horizontal spread and transition to infection. Some clinical evidence indicates that nasopharyngeal carriage is harder to eradicate with antibiotics than is pneumococcal invasive disease, which may suggest that colonizing pneumococci exist in biofilm communities that are more resistant to antibiotics. While pneumococcal biofilms have been observed during symptomatic infection, their role in colonization and the role of host factors in this process have been less studied. Here, we show for the first time that pneumococci form highly structured biofilm communities during colonization of the murine nasopharynx that display increased antibiotic resistance. Furthermore, pneumococcal biofilms grown on respiratory epithelial cells exhibited phenotypes similar to those observed during colonization in vivo, whereas abiotic surfaces produced less ordered and more antibiotic-sensitive biofilms. The importance of bacterial-epithelial cell interactions during biofilm formation was shown using both clinical strains with variable colonization efficacies and pneumococcal mutants with impaired colonization characteristics in vivo. In both cases, the ability of strains to form biofilms on epithelial cells directly correlated with their ability to colonize the nasopharynx in vivo, with colonization-deficient strains forming less structured and more antibiotic-sensitive biofilms on epithelial cells, an association that was lost when grown on abiotic surfaces. Thus, these studies emphasize the importance of host-bacterial interactions in pneumococcal biofilm formation and provide the first experimental data to explain the high resistance of pneumococcal colonization to eradication by antibiotics.

Protection against pneumococcal infection elicited by immunization with glutamyl tRNA synthetase, polyamine transport protein D and sortase A

Protein-based vaccines are considered to be the next-generation of pneumococcal vaccines. Here we evaluated the protection elicited by immunization with recombinant glutamyl tRNA synthetase (Gts), polyamine transport protein D (PotD) and sortase A (SrtA) antigens in preclinical mouse models. In mucosal immunization studies, intranasal immunization with either Gts, PotD or SrtA could significantly reduce pneumococcal nasopharyngeal and lung colonization and significantly increase mice survival times following invasive pneumococcal challenge, and combinations of these antigens could enhance this protection. In systemic immunization studies, intraperitoneal immunization with multiple protein antigens also provided better protection against pneumococcal sepsis caused by different pneumococcal strains. Finally, passive immunization studies showed an additive effect by using multiple anti-sera when compared to single anti-sera. Therefore, a multicomponent protein-based pneumococcal vaccine composed of Gts, PotD or SrtA could confer protection against pneumococcal colonization as well as invasive infections in terms of efficacy of protection and serotype coverage.

Histatin 5 uptake by Candida albicans utilizes polyamine transporters Dur3 and Dur31 proteins

Histatin 5 (Hst 5) is a salivary gland-secreted cationic peptide with potent fungicidal activity against Candida albicans. Hst 5 kills fungal cells following intracellular translocation, although its selective transport mechanism is unknown. C. albicans cells grown in the presence of polyamines were resistant to Hst 5 due to reduced intracellular uptake, suggesting that this cationic peptide may enter candidal cells through native yeast polyamine transporters. Based upon homology to known Saccharomyces cerevisiae polyamine permeases, we identified six C. albicans Dur polyamine transporter family members and propose a new nomenclature. Gene deletion mutants were constructed for C. albicans polyamine transporters Dur3, Dur31, Dur33, Dur34, and were tested for Hst 5 sensitivity and uptake of spermidine. We found spermidine uptake and Hst 5 mediated killing were decreased significantly in Δdur3, Δdur31, and Δdur3/Δdur31 strains; whereas a DUR3 overexpression strain increased Hst 5 sensitivity and higher spermidine uptake. Treatment of cells with a spermidine synthase inhibitor increased spermidine uptake and Hst 5 killing, whereas protonophores and cold treatment reduced spermidine uptake. Inhibition assays showed that Hst 5 is a competitive analog of spermidine for uptake into C. albicans cells, and that Hst 5 Ki values were increased by 80-fold in Δdur3/Δdur31 cells. Thus, Dur3p and Dur31p are preferential spermidine transporters used by Hst 5 for its entry into candidal cells. Understanding of polyamine transporter-mediated internalization of Hst 5 provides new insights into the uptake mechanism for C. albicans toxicity, and further suggests design for targeted fungal therapeutic agents.

Next generation pneumococcal vaccines

Currently licensed pneumococcal vaccines are based on the generation of antibodies to the pneumococcal polysaccharide, of which there are more than 90 different types. While these vaccines are highly effective against the serotypes included, their high cost and limited serotype coverage limit their usefulness worldwide, particularly in low resource areas. Thus alternative or adjunctive options are being actively pursued. This review will present these various approaches, including variations of the polysaccharide-protein conjugate strategy, protein-based strategies, and whole cell pneumococcal vaccines. The immunological basis for these different approaches is discussed as well.

Polyamine biosynthesis and transport mechanisms are crucial for fitness and pathogenesis of Streptococcus pneumoniae

Polyamines such as cadaverine, putrescine and spermidine are polycationic molecules that have pleiotropic effects on cells via their interaction with nucleic acids. Streptococcus pneumoniae (the pneumococcus) is a Gram-positive pathogen capable of causing pneumonia, septicaemia, otitis media and meningitis. Pneumococci have a polyamine transport operon (potABCD) responsible for the binding and transport of putrescine and spermidine, and can synthesize cadaverine and spermidine using their lysine decarboxylase (cad) and spermidine synthase (speE) enzymes. Previous studies from our laboratory have shown that an increase in PotD expression is seen following exposure to various stresses, while during infection, potD inactivation significantly attenuates pneumococcal virulence, and anti-PotD immune responses are protective in mice. In spite of their relative importance, not much is known about the global contribution of polyamine biosynthesis and transport pathways to pneumococcal disease. Mutants deficient in polyamine biosynthesis (ΔspeE or Δcad) or transport genes (ΔpotABCD) were constructed and were found to be attenuated in murine models of pneumococcal colonization and pneumonia, either alone or in competition with the wild-type strain. The ΔspeE mutant was also attenuated during invasive disease, while the potABCD and cad genes seemed to be dispensable. HPLC analyses showed reduced intracellular polyamine levels in all mutant strains compared with wild-type bacteria. High-throughput proteomic analyses indicated reduced expression of growth, replication and virulence factors in mutant strains. Thus, polyamine biosynthesis and transport mechanisms are intricately linked to the fitness, survival and pathogenesis of the pneumococcus in host microenvironments, and may represent important targets for prophylactic and therapeutic interventions.

Immunization with DnaJ (hsp40) could elicit protection against nasopharyngeal colonization and invasive infection caused by different strains of Streptococcus pneumoniae

Increasing mortality, morbidity and economic costs have been paid to pneumococcal diseases every year. Currently, vaccination is the most promising strategy to reduce the occurrence of pneumococcal infection. In this study, we investigated the protective efficacy of immunization with recombinant DnaJ (hsp40) protein against infections of different serotypes of Streptococcus pneumoniae. We demonstrated that mucosal immunization with DnaJ antigen could induce both systemic and mucosal antibodies for DnaJ and stimulate the release of high levels of IL-10, IFN-γ and IL-17A. Moreover, this mucosal vaccination could reduce nasal or lung colonization of pneumococcus and elicit protection against different serotypes of invasive pneumococcal infections. As well, we found that intraperitoneal immunization with DnaJ could also protect against invasive infections caused by different serotypes of pneumococcus, and passive immunization with antibodies specific for DnaJ confirmed that this protection was antibody-mediated. Our results therefore support the potential of DnaJ as a conserved pneumococcal protein vaccine.

Fusobacterium nucleatum envelope protein FomA is immunogenic and binds to the salivary statherin-derived peptide

We have previously shown that one of the minimal active regions of statherin, a human salivary protein, for binding to Fusobacterium nucleatum is a YQPVPE amino acid sequence. In this study, we identified the FomA protein of F. nucleatum, which is responsible for binding to the statherin-derived YQPVPE peptide. Overlay analysis showed that a 40-kDa protein of the F. nucleatum cell envelope (40-kDa CE) specifically bound to the YQPVPE peptide. The equilibrium association constant between the affinity-purified 40-kDa CE and the YQPVPE peptide was 4.30 x 10(6). Further, the purity and amino acid sequence analyses of the purified 40-kDa CE revealed approximately 98.7% (wt/wt) purity and a high degree of homology with FomA, a major porin protein of F. nucleatum. Thus, a FomA-deficient mutant failed to bind to the YQPVPE peptide. In addition, increased levels of a FomA-specific mucosal IgA antibody (Ab) and plasma IgG and IgA Abs were seen only in mice immunized nasally with cholera toxin (CT) and the purified 40-kDa FomA protein. Interestingly, saliva from mice that received FomA plus CT as a mucosal adjuvant nasally prevented in vitro binding of F. nucleatum to statherin-coated polyvinyl chloride plates. Taken together, these results suggest that induction of specific immunity to the 40-kDa FomA protein of F. nucleatum, which specifically binds to the statherin-derived peptide, may be an effective tool for preventing the formation of F. nucleatum biofilms in the oral cavity.

Potential role for mucosally active vaccines against pneumococcal pneumonia

Pneumococcal pneumonia is a life-threatening disease with high mortality and morbidity among children under 5 years of age, the elderly and immunocompromised individuals worldwide. Protection against pneumococcal pneumonia relies on successful regulation of colonisation in the nasopharynx and a brisk alveolar macrophage-mediated immune response in the lung. Therefore, enhancing pulmonary mucosal immunity (which includes a combination of innate, humoral and cell-mediated immunity) through mucosal vaccination might be the key to prevention of pneumococcal infection. Current challenges include a lack of information in humans on mucosal immunity against pneumococci and a lack of suitable adjuvants for new vaccines. Data from mouse models, however, suggest that mucosally active vaccines will enhance mucosal and systemic immunity for protection against pneumococcal infection.