Pneumococcal surface protein A of invasive Streptococcus pneumoniae isolates from Colombian children

Preliminary Evaluation of the Safety and Immunogenicity of a Novel Protein-Based Pneumococcal Vaccine in Healthy Adults Aged 18-49: A Phase Ia Randomized, Double Blind, Placebo-Controlled Clinical Study

Background: Protein-based pneumococcal vaccines (PBPVs) may offer expanded protection against Streptococcus pneumoniae and tackle the antimicrobial resistance crisis in pneumococcal infections. This study examined the safety and immunogenicity in healthy adults vaccinated with three doses of a protein-based pneumococcal vaccine containing pneumococcal surface protein A (PspA) (PRX1, P3296 and P5668) and in combination with a recombinant detoxified pneumolysin protein (PlyLD). Methods: This phase Ia randomized, double blind, placebo-controlled clinical study enrolled healthy adults aged 18-49 years. The participants were randomized into experimental (low-dose, medium-dose, high-dose) and placebo groups in a ratio of 3:1. Three doses of investigational vaccine were given to the participants with an interval of two months. Safety endpoints included the occurrence of total adverse reactions, solicited local and systemic adverse reactions, unsolicited adverse reactions, serious adverse events (SAEs), and several laboratory parameters. Immunogenicity endpoints included geometric mean titers (GMT) of anti-PspA (PRX1, P3296 and P5668) and anti-PlyLD antibodies level as determined by ELISA, seropositivity rates of PspA and PlyLD antibodies (>4-fold increase) and neutralization activity of anti-Ply antibody in serum. Results: A total of 118 participants completed the study of three doses. The candidate PBPV was safe and well-tolerated in all experimental groups. No vaccine-related SAEs were observed in this study. Most solicited adverse reactions were mild and transient. The most frequently reported solicited adverse reactions in the medium- and high-dose groups was pain at the injection site, while in the low-dose group it was elevated blood pressure. The immunogenicity data showed a sharp increase in the GMT level of anti-PspA-RX1, anti-PspA-3296, anti-PspA-5668, and anti-PlyLD antibodies in serum. The results also showed that the elicited antibodies were dosage-dependent. The high-dose group showed a higher immune response against PspA-RX1, PspA-3296, PspA-5668, and PlyLD antigens. However, repeat vaccination did not increase the level of anti-PspA antibodies but the level of anti-PlyLD antibody. High seropositivity rates were also observed for anti-PspA-RX1, anti-PspA-3296, anti-PspA-5668, and anti-PlyLD antibodies. In addition, a significant difference in the GMT levels of anti-Ply antibody between the high-, medium-, and low-dose groups post each vaccination were indicated by neutralization activity tests. Conclusions: The PBPV showed a safe and immunogenic profile in this clinical trial. Taking into consideration both safety and immunogenicity data, we propose a single dose of 50 µg (medium dose) of PBPV as the optimum approach in providing expanded protection against Streptococcus pneumoniae.

Establishment of a modified opsonophagocytic killing assay for anti-pneumococcal surface protein A antibody

Streptococcus pneumoniae (pneumococcus) is a pathogenic gram-positive bacterium that causes pneumonia, meningitis, and sepsis. Pneumococcal surface protein A (PspA) induces antibodies that protect against lethal infections by pneumococci. PspA is a choline-binding protein present on the cell surface of almost all pneumococcal strains and is a non-capsular polysaccharide vaccine candidate. For research and development of PspA-based vaccines, an in-vitro test system to measure the activity of functional antibodies capable of killing pneumococci is essential. The opsonophagocytic killing (OPK) assay is used to evaluate the opsonic activity of functional antibodies induced by capsular polysaccharide (CPS)-based vaccines (standard OPK assay). Despite the potential of anti-PspA antibodies to protect against lethal infections in mice, the standard OPK assay fails to evaluate anti-PspA antibodies. Using a pneumococcal surface protein C-deficient strain and extending the incubation time of opsonized bacteria, complement, and HL-60 cells reportedly results in enhanced bactericidal activity (modified OPK assay). We aimed to measure the bactericidal activity of anti-PspA antibodies in intact pneumococcal strains. We optimized the pneumococcal culture method used in the OPK assay to increase the efficiency of anti-PspA antibody-mediated phagocytosis of HL-60 cells. As thick capsules hinder phagocytosis, we attempted to obtain pneumococci with thin capsules through an improved culture method. As pneumococci attached to cells exhibit thin capsules, pneumococci cultured in Todd Hewitt yeast extract (THY) broth were spread on blood agar plates and incubated for 4 h. cpsA mRNA transcript levels in pneumococci cultured on blood agar were lower than those in pneumococci cultured in THY broth. OPK activity against pneumococci expressing PspA of clades 1-5 was reasonably well detected using pneumococci cultured on blood agar in the modified OPK assay. The modified OPK assay for anti-PspA antibody using pneumococci cultured on blood agar represents a useful assay to determine the killing activity of functional anti-PspA antibodies against pneumococci.

Immune responses and protection against Streptococcus pneumoniae elicited by recombinant Bordetella pertussis adenylate cyclase (CyaA) carrying fragments of pneumococcal surface protein A, PspA

Streptococcus pneumoniae is a common agent of important human diseases such as otitis media, pneumonia, meningitis and sepsis. Current available vaccines that target capsular polysaccharides induce protection against invasive disease and nasopharyngeal colonization in children, yet their efficacy is limited to the serotypes included in the formulations. The virulence factor Pneumococcal Surface Protein A (PspA) interacts with host immune system and helps the bacteria to evade phagocytosis. Due to its essential role in virulence, PspA is an important vaccine candidate. Here we have tested a delivery system based on the adenylate cyclase toxin of Bordetella pertussis (CyaA) to induce immune responses against PspA in mice. CyaA was engineered to express fragments of the N-terminal region of PspAs from clades 2 and 4 (A2 and A4) and the resulting proteins were used in immunization experiments in mice. The recombinant CyaA-A2 and CyaA-A4 proteins were able to induce high levels of anti-PspA antibodies that reacted with pneumococcal strains expressing either PspA2 or PspA4. Moreover, reactivity of the antibodies against pneumococcal strains that express PspAs from clades 3 and 5 (PspA3 and PspA5) was also observed. A formulation containing CyaA-A2 and CyaA-A4 was able to protect mice against invasive pneumococcal challenges with isolates that express PspA2, PspA4 or PspA5. Moreover, a CyaA-A2-A4 fusion protein induced antibodies at similar levels and with similar reactivity as the formulation containing both proteins, and protected mice against the invasive challenge. Our results indicate that CyaA-PspA proteins are good candidates to induce broad protection against pneumococcal isolates.

Carriage prevalence, serotype distribution, antimicrobial resistance, pspA typing and pilus islets of Streptococcus pneumoniae isolated from adults living in a Brazilian urban slum

INTRODUCTION

For Brazilian adults, pneumococcal vaccines have been usually taken only by those who are at higher risk for development of pneumococcal diseases. Since populations from lower socioeconomic status are at high risk of acquiring pneumococcal infections, we investigated the carriage prevalence, colonization risk factors, capsular and surface protein types, and antimicrobial resistance among pneumococcal isolates recovered from adults living in a Brazilian urban slum.

METHODS

Between September-December 2016, we conducted a cross-sectional study among individuals aged ≥ 18 years who attended a public primary clinic in Niterói/RJ, Brazil. Pneumococci were isolated by culture on sheep blood agar plates with and without gentamicin. Antimicrobial susceptibility was determined for all isolates. We used PCR to determine capsular types, PspA families (Fam) and pilus islets (PI).

RESULTS

Of 385 adults, 32 (8.3 %) were pneumococcal carriers. Three carriers had two different pneumococci, totaling 35 isolates. After multivariate analysis, smoking, previous hospitalization, alcohol consumption and co-habitation with children aged < 6 years increased the odds of pneumococcal carriage, but antibiotic use in the previous 2 weeks was found to be a protective factor. Fourteen different serogroups/serotypes were detected and the prevalent ones were 9 N/L, 10A, 15B/C and 35F/47F (n = 3; 8.6 % each). Non-typeable (NT) isolates made up 31.4 %. All isolates were susceptible to chloramphenicol, levofloxacin and vancomycin. We found eight (22.9 %) penicillin non-susceptible pneumococci (PNSP) with minimum inhibitory concentrations (MICs) of 0.38-1.5 μg/mL. The two (5.7 %) erythromycin-resistant isolates had MIC > 256 μg/mL, cMLS_B phenotype and the erm(B) gene. Twelve (34.3 %) and 17 (48.6 %) isolates had PspA Fam1 and Fam2, respectively. Three (8.6 %) isolates had genes for pilitwo PI-1 and one PI-2.

CONCLUSION

We detected a low frequency of pneumococcal carriage among the adult population, but a high diversity of serotypes. Frequencies of PNSP and NT isolates resistant to antimicrobial agents are concerning.

A Jack of All Trades: The Role of Pneumococcal Surface Protein A in the Pathogenesis of Streptococcus pneumoniae

Streptococcus pneumoniae (Spn), or the pneumococcus, is a Gram-positive bacterium that colonizes the upper airway. Spn is an opportunistic pathogen capable of life-threatening disease should it become established in the lungs, gain access to the bloodstream, or disseminate to vital organs including the central nervous system. Spn is encapsulated, allowing it to avoid phagocytosis, and current preventative measures against infection include polyvalent vaccines composed of capsular polysaccharide corresponding to its most prevalent serotypes. The pneumococcus also has a plethora of surface components that allow the bacteria to adhere to host cells, facilitate the evasion of the immune system, and obtain vital nutrients; one family of these are the choline-binding proteins (CBPs). Pneumococcal surface protein A (PspA) is one of the most abundant CBPs and confers protection against the host by inhibiting recognition by C-reactive protein and neutralizing the antimicrobial peptide lactoferricin. Recently our group has identified two new roles for PspA: binding to dying host cells via host-cell bound glyceraldehyde 3-phosphate dehydrogenase and co-opting of host lactate dehydrogenase to enhance lactate availability. These properties have been shown to influence Spn localization and enhance virulence in the lower airway, respectively. Herein, we review the impact of CBPs, and in particular PspA, on pneumococcal pathogenesis. We discuss the potential and limitations of using PspA as a conserved vaccine antigen in a conjugate vaccine formulation. PspA is a vital component of the pneumococcal virulence arsenal - therefore, understanding the molecular aspects of this protein is essential in understanding pneumococcal pathogenesis and utilizing PspA as a target for treating or preventing pneumococcal pneumonia.

Serum levels of anti-PspA and anti-PspC IgG decrease with age and do not correlate with susceptibility to experimental human pneumococcal colonization

Older adults are at increased risk of pneumococcal disease. This work aims to evaluate whether there is any decrease in serum IgG against variants of the antigens Pneumococcal surface protein A (PspA) and Pneumococcal surface protein C (PspC) in healthy adults with increasing age. Levels of IgG against PspA and PspC variants were determined by ELISA in serum samples comparing volunteers 18–30 years of age with volunteers who were 50–70+ before and after an experimental pneumococcal colonization challenge. The serotype 6B strain used in the challenge belongs to a minor group of pneumococcal isolates expressing two PspC variants. There was a decrease in levels of IgG with increasing age for the most common PspA variants and for all PspC variants analyzed. No correlation was found between basal levels of IgG against these antigens and protection against colonization. There was an increase in levels of IgG against PspA variants that are more cross-reactive with the variant expressed by the challenge strain post challenge in younger individuals who became colonized. Since the challenge strain used in our study expresses two different PspC variants, an increase in serum IgG against all PspC variants tested was observed in younger individuals who became colonized. For some of the antigen variants tested, a decrease in serum IgG was observed in young volunteers who were challenged but did not become colonized. Serum IgG antibodies against PspA and PspC variants thus decrease with age in healthy adults, but there is no correlation between levels of IgG against these antigens and protection against human experimental colonization. Though no correlation between naturally induced serum IgG antibodies against PspA and PspC and protection against colonization was observed, these results do not rule out the protective potential of these antigens as vaccines against pneumococcal infections.

Virulence-Associated Characteristics of Serotype 14 and Serogroup 9 Streptococcus pneumoniae Clones Circulating in Brazil: Association of Penicillin Non-susceptibility With Transparent Colony Phenotype Variants

Streptococcus pneumoniae remains a major agent of invasive diseases, especially in children and the elderly. The presence of pneumococcal capsule, pneumococcal surface protein A (PspA), and pilus type 1 (PI-1) and the ability of colony phase variation are assumed to play important roles in the virulence potential of this microorganism. Differences in the capsular polysaccharide allow the characterization of more than 90 pneumococcal serotypes; among them, serotype 14 and serogroup 9 stand out due to their prevalence in the pre- pneumococcal conjugate vaccine era and frequent association with penicillin non-susceptibility. Here we investigated the distribution of PI-1 and pspA genes and colony phase variants among 315 S. pneumoniae isolates belonging to serotype 14 and serogroup 9, recovered over 20 years in Brazil, and correlated these characteristics with penicillin susceptibility and genotype as determined by multilocus sequence typing. All strains were shown to carry pspA genes, with those of family 2 (pspA2) being the most common, and nearly half of the strains harbored P1-1 genes. The pspA gene family and the presence of PI-1 genes were conserved features among strains belonging to a given clone. A trend for increasing the occurrence of pspA2 and PI-1 genes over the period of investigation was observed, and it coincided with the dissemination of CC156 (Spain^9V-3) clone in Brazil, suggesting a role for these virulence attributes in the establishment and the persistence of this successful clone. Opaque variant was the colony phenotype most frequently observed, regardless of clonal type. On the other hand, the transparent variant was more commonly associated with penicillin-non-susceptible pneumococci and with strains presenting evidence of recombination events involving the genes coding for polysaccharide capsule and PspA, suggesting that pneumococcal transparent variants may present a higher ability to acquire exogenous DNA. The results bring to light new information about the virulence potentials of serotype 14 and serogroup 9 S. pneumoniae isolates representing the major clones that have been associated with the emergence and the dissemination of antimicrobial resistance in our setting since the late 1980s.

[Regional System for Vaccines (SIREVA), laboratory surveillance and vaccine development for Streptococcus pneumoniae: bibliometric analysis, 1993-2019]

Objetivo.

Medir a través del análisis bibliométrico la productividad, la visibilidad y el impacto del Sistema Regional de Vacunas (SIREVA, un proyecto de la Organización Panamericana de la Salud) en sus dos componentes, la vigilancia por laboratorio y el desarrollo de vacunas.

Métodos.

Se recuperaron de Scopus las publicaciones correspondientes a vigilancia por laboratorio y desarrollo de vacunas con sus referencias y citas y se aplicó la herramienta para obtener los indicadores bibliométricos. Se utilizó VOSviewer^® 1.6.13 para visualizar las redes de coautoría por país y autores, y para realizar un análisis de coocurrencia de términos incluidos en los títulos y resúmenes de las publicaciones.

Resultados.

Cumplieron los criterios establecidos para vigilancia por laboratorio y desarrollo de vacunas 173 y 128 publicaciones, respectivamente. Diez países de la Región fueron responsables de 90,8% de las publicaciones sobre vigilancia por laboratorio y 8 países de todas las publicaciones sobre desarrollo de vacunas. Las diez publicaciones más citadas sobre vigilancia por laboratorio y sobre desarrollo de vacunas estaban incluidas en 855 y 503 artículos, respectivamente; los principales autores se encontraban en Alemania, Australia, Bélgica, Brasil, China, Estados Unidos de América y el Reino Unido. La construcción y visualización de redes por coautorías de autores y países, y la coocurrencia de términos mostraron el trabajo en red y la colaboración intrarregional, así como permitieron hacer seguimiento a las diversas áreas de estudio y su evolución en el tiempo.

Conclusiones.

El análisis bibliométrico permitió documentar de manera objetiva la productividad y visibilidad del Sistema Regional de Vacunas para Streptococcus pneumoniae en la Región.

Prevalence of PspA families and pilus islets among Streptococcus pneumoniae colonizing children before and after universal use of pneumococcal conjugate vaccines in Brazil

In 2010, the 10-valent (PCV10) and 13-valent (PCV13) pneumococcal conjugate vaccines were introduced in Brazil to immunize children, resulting in serotype replacement. We analyzed 253 carriage isolates recovered from children aged <6 years in Brazil, including 124 and 129 isolates from the pre-PCV10/13 (December 2009-July 2010) and post-PCV10/13 (September-December 2014) periods, respectively, to investigate the prevalence of PspA families and pilus islets, potential vaccine candidates. Serotypes and resistance profiles were previously characterized. We used PCR to type PspA families (Fam1-3) and pilus islets (PI-1 and PI-2). We identified the PspA family of 130 (51.4%) isolates. PspA families 1, 2, and 3 were identified in 12.2%, 38.7%, and 0.4% of the isolates, respectively. Eighteen (58.1%) Fam1 isolates were serogroup 6. Nine (81.8%) of 11 serotype 14 isolates were Fam2. Fam1 isolates resistant to penicillin (50%), erythromycin (43.7%), clindamycin (31.2%), and chloramphenicol (6.2%) were only found after PCV10/13 introduction. Resistance among Fam2 isolates was higher in the post-PCV10/13 period to erythromycin (1.8% vs. 18.6%), clindamycin (0 vs. 13.9%), and tetracycline (10.9% vs. 16.3%). PI-I was detected in 42 (16.6%) isolates. Fourteen (56%) of 25 serotype 15B/C and nine (81.8%) of 11 serotype 14 isolates had PI-1 (p < 0.01). Eight (3.2%) isolates had PI-2, and six (75%) were serogroup 19. Five (2%) serogroup 19 isolates had both PI-1 and PI-2. We found associations between serogroups/serotypes, PspA families, and pilus islets, but distribution of PspA families and pilus islets was similar in both periods. After universal vaccination, we observed higher antimicrobial resistance frequencies, regardless PspA or pilus types.

Prevalence of PspA families and pilus islets among Streptococcus pneumoniae colonizing children before and after universal use of pneumococcal conjugate vaccines in Brazil

In 2010, the 10-valent (PCV10) and 13-valent (PCV13) pneumococcal conjugate vaccines were introduced in Brazil to immunize children, resulting in serotype replacement. We analyzed 253 carriage isolates recovered from children aged <6 years in Brazil, including 124 and 129 isolates from the pre-PCV10/13 (December 2009-July 2010) and post-PCV10/13 (September-December 2014) periods, respectively, to investigate the prevalence of PspA families and pilus islets, potential vaccine candidates. Serotypes and resistance profiles were previously characterized. We used PCR to type PspA families (Fam1-3) and pilus islets (PI-1 and PI-2). We identified the PspA family of 130 (51.4%) isolates. PspA families 1, 2, and 3 were identified in 12.2%, 38.7%, and 0.4% of the isolates, respectively. Eighteen (58.1%) Fam1 isolates were serogroup 6. Nine (81.8%) of 11 serotype 14 isolates were Fam2. Fam1 isolates resistant to penicillin (50%), erythromycin (43.7%), clindamycin (31.2%), and chloramphenicol (6.2%) were only found after PCV10/13 introduction. Resistance among Fam2 isolates was higher in the post-PCV10/13 period to erythromycin (1.8% vs. 18.6%), clindamycin (0 vs. 13.9%), and tetracycline (10.9% vs. 16.3%). PI-I was detected in 42 (16.6%) isolates. Fourteen (56%) of 25 serotype 15B/C and nine (81.8%) of 11 serotype 14 isolates had PI-1 (p < 0.01). Eight (3.2%) isolates had PI-2, and six (75%) were serogroup 19. Five (2%) serogroup 19 isolates had both PI-1 and PI-2. We found associations between serogroups/serotypes, PspA families, and pilus islets, but distribution of PspA families and pilus islets was similar in both periods. After universal vaccination, we observed higher antimicrobial resistance frequencies, regardless PspA or pilus types.

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.

PspA facilitates evasion of pneumococci from bactericidal activity of neutrophil extracellular traps (NETs)

Pneumococcal strains are variably resistant to killing by neutrophil extracellular traps (NETs). We hypothesize that this variability in resistance is due to heterogeneity in pneumococcal surface protein A (PspA), a structurally diverse virulence factor of Streptococcus pneumoniae. Pneumococcal strains showed variability in induction of NETs and in susceptibility to killing by NETs. The variability in susceptibility to NETs-mediated killing of pneumococcal strains is attributed to PspA, as strains lacking the surface expression of PspA were significantly more sensitive to NETs-mediated killing compared to the wild-type strains. Using pspA switch mutants we were further able to demonstrate that NETs induction and killing by NETs is a function of PspA as mutants with switch PspA demonstrated donor phenotype. Antibody to PspA alone showed an increase in induction of NETs, and NETs thus generated were able to trap and kill pneumococci. Pneumococci opsonized with antibody to PspA showed increase adherence to NETs but a decrease susceptibility to killing by NETs. In conclusion we demonstrate a novel role for pneumococcal PspA in resisting NETs mediated killing and allowing the bacteria to escape containment by blocking binding of pneumococci to NETs.

Comparison of four adjuvants revealed the strongest protection against lethal pneumococcal challenge following immunization with PsaA-PspA fusion protein and AS02 as adjuvant

Streptococcuspneumoniae, or pneumococcus, is a major respiratory-tract pathogen that causes high levels of mortality and morbidity in infants and elderly individuals. Despite the development of various capsular polysaccharide vaccines to prevent pneumococcal disease, it remains epidemic. Pneumococcal surface protein A (PspA) is a highly immunogenic surface protein existing in all strains of S. pneumoniae, and it can elicit immunizing protection against pneumococcal infection. In our previous studies, a fusion protein (PsaA-PspA23), consisting of PspA and pneumococcal surface antigen A (PsaA), displayed greater immunogenicity and provided better protection in mice against S. pneumoniae strains than either PsaA or PspA. In this study, the fusion protein PsaA-PspA23, together with PspA4, was formulated with four adjuvants Al(OH)₃, MF59, AS03, and AS02, and subsequently subjected to dose optimization and immunological evaluation for determination of the antibody titers, bacterial burden, survival rates, and levels of cytokines in mice. All vaccines with high adjuvant doses displayed higher antigen-specific immunoglobulin G (IgG) titers. Bacterial burdens were notably decreased to different extents in the lungs and blood of mice immunized with the antigen and various adjuvants. Among these adjuvants, AS02 provided outstanding protection against challenge with pathogenic bacteria from different families and clades; it also induced high titers of IgG1 and IgG2a. Moreover, only AS02 elicited high levels of cytokines, such as TNF-α, IFN-γ, IL-2, and IL-4. These results suggest that PsaA-PspA23 and PspA4 formulated with AS02 may potentially be used as a subunit vaccine against deadly pneumococcal infection.

The diversity of the proline-rich domain of pneumococcal surface protein A (PspA): Potential relevance to a broad-spectrum vaccine

Pneumococcal surface protein A (PspA) is a surface exposed, highly immunogenic protein of Streptococcus pneumoniae. Its N-terminal α-helical domain (αHD) elicits protective antibody in humans and animals that can protect mice from fatal infections with pneumococci and can be detected in vitro with opsonophagocytosis assays. The proline-rich domain (PRD) in the center of the PspA sequence can also elicit protection. This study revealed that although the sequence of PRD was diverse, PRD from different pneumococcal isolates contained many shared elements. The inferred amino acid sequences of 123 such PRDs, which were analyzed by assembly and alignment-free (AAF) approaches, formed three PRD groups. Of these sequences, 45 were classified as Group 1, 19 were classified as Group 2, and 59 were classified as Group 3. All Group 3 sequences contained a highly conserved 22-amino acid non-proline block (NPB). A significant polymorphism was observed, however, at a single amino acid position within NPB. Each of the three PRD groups had characteristic patterns of short amino acid repeats, with most of the repeats being found in more than one PRD group. One of these repeats, PKPEQP as well as the NPB were previously shown to elicit protective antibodies in mice. In this study, we found that sera from 12 healthy human adult volunteers contained antibodies to all three PRD groups. This suggested that a PspA-containing vaccine containing carefully selected PRDs and αHDs could redundantly cover the known diversity of PspA. Such an approach might reduce the chances of PspA variants escaping a PspA vaccine's immunity.

Genetic diversity of pneumococcal surface protein A (PspA) in paediatric isolates of non-conjugate vaccine serotypes in Japan

PURPOSE

Among the pneumococcal proteins, pneumococcal surface protein A (PspA) is considered the most promising candidate for a serotype-independent vaccine. This study aimed to investigate the serotype, genetic diversity of PspA, lineage (genotype) and drug resistance traits of pneumococcal isolates from paediatric patients.

METHODOLOGY

A total of 678 non-invasive pneumococcal isolates obtained from June to November 2016 were analysed. All isolates were characterized for PspA families, serotypes and macrolide resistance genes. Seventy-one representative isolates of non-vaccine serotypes (NVTs) were genetically analysed for the clade-defining region (CDR) of PspA, as well as multi-locus sequence typing (MLST).

RESULTS

The detection rate of NVTs was 87.9 % (n=596), including dominant NVTs 15A (14.5 %, n=98), 35B (11.8 %, n=80), 15C (9.3 %, n=63) and 23A (9.0 %, n=61). Most isolates (96.6 %) possessed macrolide resistance genes erm(B) and/or mef(A/E). PspA families 1, 2 and 3 were detected in 42.3, 56.6 and 0.6 % of isolates, respectively. Nucleotide sequences of CDR showed high identity (90-100 %) within the same PspA clade, although the CDR identity among different PspA families ranged from 53 to 69 %. All isolates of NVTs 23A, 10A, 34, 24, 22F/22A, 33F, 23B and 38 were from PspA family 1, while NVTs 35B, 15C, 15B and 11A/11D isolates were from family 2. In contrast, genetically distinct PspAs were found in NVTs 6C and 15A. PspA family 3/clade 6 was detected in only NVT serotype 37 isolates assigned to ST447 and ST7970, showing the mucoid phenotype.

CONCLUSION

The present study revealed the predominance of PspA families 1 and 2 in NVTs, and the presence of family 3 in serotype 37.

Genetic diversity of pneumococcal surface protein A in invasive pneumococcal isolates from Korean children, 1991-2016

Pneumococcal surface protein A (PspA) is an important virulence factor of pneumococci and has been investigated as a primary component of a capsular serotype-independent pneumococcal vaccine. Thus, we sought to determine the genetic diversity of PspA to explore its potential as a vaccine candidate. Among the 190 invasive pneumococcal isolates collected from Korean children between 1991 and 2016, two (1.1%) isolates were found to have no pspA by multiple polymerase chain reactions. The full length pspA genes from 185 pneumococcal isolates were sequenced. The length of pspA varied, ranging from 1,719 to 2,301 base pairs with 55.7–100% nucleotide identity. Based on the sequences of the clade-defining regions, 68.7% and 49.7% were in PspA family 2 and clade 3/family 2, respectively. PspA clade types were correlated with genotypes using multilocus sequence typing and divided into several subclades based on diversity analysis of the N-terminal α-helical regions, which showed nucleotide sequence identities of 45.7–100% and amino acid sequence identities of 23.1–100%. Putative antigenicity plots were also diverse among individual clades and subclades. The differences in antigenicity patterns were concentrated within the N-terminal 120 amino acids. In conclusion, the N-terminal α-helical domain, which is known to be the major immunogenic portion of PspA, is genetically variable and should be further evaluated for antigenic differences and cross-reactivity between various PspA types from pneumococcal isolates.

Production and purification of an untagged recombinant pneumococcal surface protein A (PspA4Pro) with high-purity and low endotoxin content

Streptococcus pneumoniae is the main cause of pneumonia, meningitis, and other conditions that kill thousands of children every year worldwide. The replacement of pneumococcal serotypes among the vaccinated population has evidenced the need for new vaccines with broader coverage and driven the research for protein-based vaccines. Pneumococcal surface protein A (PspA) protects S. pneumoniae from the bactericidal effect of human apolactoferrin and prevents complement deposition. Several studies indicate that PspA is a very promising target for novel vaccine formulations. Here we describe a production and purification process for an untagged recombinant fragment of PspA from clade 4 (PspA4Pro), which has been shown to be cross-reactive with several PspA variants. PspA4Pro was obtained using lactose as inducer in Phytone auto-induction batch or glycerol limited fed-batch in 5-L bioreactor. The purification process includes two novel steps: (i) clarification using a cationic detergent to precipitate contaminant proteins, nucleic acids, and other negatively charged molecules as the lipopolysaccharide, which is the major endotoxin; and (ii) cryoprecipitation that eliminates aggregates and contaminants, which precipitate at -20 °C and pH 4.0, leaving PspA4Pro in the supernatant. The final process consisted of cell rupture in a continuous high-pressure homogenizer, clarification, anion exchange chromatography, cryoprecipitation, and cation exchange chromatography. This process avoided costly tag removal steps and recovered 35.3 ± 2.5% of PspA4Pro with 97.8 ± 0.36% purity and reduced endotoxin concentration by >99.9%. Circular dichroism and lactoferrin binding assay showed that PspA4Pro secondary structure and biological activity were preserved after purification and remained stable in a wide range of temperatures and pH values.

The effects of differences in pspA alleles and capsular types on the resistance of Streptococcus pneumoniae to killing by apolactoferrin

Pneumococcal surface protein A (PspA) is the only pneumococcal surface protein known to strongly bind lactoferrin on the bacterial surface. In the absence of PspA Streptococcus pneumoniae becomes more susceptible to killing by human apolactoferrin (apo-hLf), the iron-free form of lactoferrin. In the present study we examined diverse strains of S. pneumoniae that differed by 2 logs in their susceptibility to apo-hLf. Among these strains, the amount of apo-hLf that bound to cell surface PspA correlated directly with the resistance of the strain to killing by apo-hLf. Moreover examination of different pspA alleles on shared genetic backgrounds revealed that those PspAs that bound more lactoferrin conferred greater resistance to killing by apo-hLf. The effects of capsule on killing of pneumococci by apo-hLf were generally small, but on one genetic background, however, the lack of capsule was associated with 4-times as much apo-hLf binding and 30-times more resistance to killing by apo-hLf. Overall these finding strongly support the hypothesis that most of the variation in the ability of apo-hLf is dependent on the variation in the binding of apo-hLf to surface PspA and this binding is dependent on variation in PspA as well as variation in capsule which may enhance killing by reducing the binding of apo-hLf to PspA.

Pertussis toxin improves immune responses to a combined pneumococcal antigen and leads to enhanced protection against Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is a candidate antigen for the composition of protein-based vaccines against Streptococcus pneumoniae. While searching for efficient adjuvants for PspA-based vaccines, our group has described the potential of combining PspA with the whole-cell pertussis vaccine (wP). When given to mice through the nasal route, a formulation composed of PspA from clade 5 (PspA5) and wP (PspA5-wP) induced high levels of antibodies and protection against challenges with different pneumococcal strains. PspA5-wP also induced the secretion of interleukin 17 (IL-17) by splenocytes and the infiltration of leukocytes in the lungs after challenge. Here, we show that protection against a pneumococcal invasive challenge was completely abrogated in μMT(-/-) mice, which are deficient in the maturation of B cells, illustrating the importance of antibodies in the survival elicited by the PspA5-wP vaccine. Moreover, passive immunization showed that IgG purified from the sera of mice immunized with PspA5-wP conferred significant protection to naive mice, whereas the respective F(ab')2 did not. Additionally, in vivo depletion of complement abolished protection against the pneumococcal challenge. The combination of PspA5 with wild-type or mutant Bordetella pertussis strains or with purified components showed that the pertussis toxin (PT)-containing formulations induced the highest levels of antibodies and protection. This suggests that the adjuvant activity of wP in the PspA5 model is mediated at least in part by PT. The sera from mice immunized with such formulations displayed high IgG binding and induction of complement deposition on the pneumococcal surface in vitro, which is consistent with the in vivo results.

Invasive and noninvasive Streptococcus pneumoniae capsule and surface protein diversity following the use of a conjugate vaccine

The 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the United States in 2010 for the prevention of invasive pneumococcal disease (IPD) and otitis media. While many studies have reported its potential efficacy for IPD, not much is known about the epidemiology of noninvasive disease following its introduction. We characterized the capsular types and surface protein genes of noninvasive pediatric pneumococcal isolates collected between 2002 and 2010 (n = 1,058) at Children's of Alabama following the introduction of PCV7 and tested a subset of noninvasive and previously characterized IPD isolates for the presence of the pspA, pspC, and rrgC genes, which encode protection-eliciting proteins. PCV7 serotypes had dramatically decreased by 2010 (P < 0.0001), and only 50% of all noninvasive infections were caused by the PCV13 capsular serotypes. Serotype 19A accounted for 32% of the noninvasive isolates, followed by serotypes 35B (9%), 19F (7%), and 6C (6%). After 7 years of PCV7 usage, there were no changes in the frequencies of the pspA or pspC genes; 96% of the strains were positive for family 1 or 2 pspA genes, and 81% were also positive for pspC. Unexpectedly, more noninvasive than invasive strains were positive for rrgC (P < 0.0001), and the proportion of rrgC-positive strains in 2008 to 2010 was greater than that in 2002 to 2008 (IPD, P < 0.02; noninvasive, P < 0.001). Serotypes 19F, 19A, and 35B were more frequently rrgC positive (P < 0.005) than other serotypes. A vaccine containing antigens, such as PspA, PspC, and/or RrgC, can provide coverage against most non-PCV13-type pneumococci. Continued surveillance is critical for optimal future vaccine development.

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.

Modified opsonization, phagocytosis, and killing assays to measure potentially protective antibodies against pneumococcal surface protein A

The standard opsonophagocytosis killing assay (OPKA) for antibodies to pneumococcal capsular polysaccharide was modified to permit an evaluation of the protection-mediating antibodies to pneumococcal surface protein A (PspA). We found that by increasing the incubation time with the complement and phagocytes from 45 min to 75 min, the protective activity was readily detected. In another modification, we used a capsule type 2 target strain that expressed PspA but not pneumococcal surface protein C (PspC). With these modifications separately or in combination, rabbit antisera to the recombinant α-helical or proline-rich domains of PspA mediated >50% killing of the target strain. The ability of normal human sera to mediate the killing of pneumococci in this modified OPKA correlated with their levels of antibodies to PspA and their ability to protect mice against fatal infection with a type 3 strain. Passive protection of mice against pneumococci and killing in the modified OPKA were lost when normal human sera were adsorbed with recombinant PspA (rPspA) on Sepharose, thus supporting the potential utility of the modified OPKA to detect protective antibodies to PspA. In the standard OPKA, monoclonal antibodies to PspA were strongly protective in the presence of subprotective amounts of anti-capsule. Thus, the currently established high-throughput OPKA for antibodies to capsule could be modified in one of two ways to permit an evaluation of the opsonic efficacy of antibodies to PspA.

Asthma and antibodies to pneumococcal virulence proteins

PURPOSE

We previously reported that asthmatics had lower anti-serotype-specific pneumococcal polysaccharide antibody levels than non-asthmatics, and the T-helper 2 (Th2) immune profile was associated with suboptimal pneumococcal polysaccharide antibody. Our objective was to determine the influence of asthma status on anti-pneumococcal protein antigen antibody levels.

METHODS

We conducted a cross-sectional study, which enrolled 16 children and adults with asthma and 14 subjects without asthma. Asthma was ascertained by predetermined criteria. Serum IgG antibody levels to pneumococcal surface protein A (PspA), pneumococcal surface protein C (PspC), pneumococcal choline-binding protein A (PcpA), and pneumolysin (PLY) were measured by enzyme-linked immunosorbent assays (ELISA). These antibody levels were compared between asthmatics and non-asthmatics. The Th2 immune profile was determined by IL-5 secretion from PBMCs cultured with house dust mite (HDM) and staphylococcal enterotoxin B (SEB) at day 7. The correlation between the anti-pneumococcal antibody levels and the Th2-HDM and SEB-responsive immune profile was assessed.

RESULTS

Of the 30 subjects, 16 (53%) were male and the median age was 26 years. There were no significant differences in anti-PspA, anti-PspC, anti-PcpA, and anti-PLY antibody levels between asthmatics and non-asthmatics. The Th2 immune profile was inversely correlated with the anti-PspC antibody levels (r = -0.53, p = 0.003). This correlation was significantly modified by asthma status (r = -0.74, p = 0.001 for asthmatics vs. r = -0.06, p = 0.83 for non-asthmatics). Other pneumococcal protein antibodies were not correlated with the Th2 immune profile.

CONCLUSION

No significant differences in the anti-pneumococcal protein antigen antibody levels between asthmatics and non-asthmatics were found. Asthma status is an important effect modifier determining the negative influence of the Th2 immune profile on anti-PspC antibody levels.

PspA family distribution, antimicrobial resistance and serotype of Streptococcus pneumoniae isolated from upper respiratory tract infections in Japan

Background

The protection against pneumococcal infections provided by currently available pneumococcal polysaccharide conjugate vaccines are restricted to the limited number of the serotypes included in the vaccine. In the present study, we evaluated the distribution of the pneumococcal capsular type and surface protein A (PspA) family of pneumococcal isolates from upper respiratory tract infections in Japan.

Methods

A total of 251 S. pneumoniae isolates from patients seeking treatment for upper respiratory tract infections were characterized for PspA family, antibiotic resistance and capsular type.

Results

Among the 251 pneumococci studied, the majority (49.4%) was identified as belonging to PspA family 2, while most of the remaining isolates (44.6%) belonged to family 1. There were no significant differences between the distributions of PspA1 versus PspA2 isolates based on the age or gender of the patient, source of the isolates or the isolates’ susceptibilities to penicillin G. In contrast, the frequency of the mefA gene presence and of serotypes 15B and 19F were statistically more common among PspA2 strains.

Conclusion

The vast majority of pneumococci isolated from the middle ear fluids, nasal discharges/sinus aspirates or pharyngeal secretions represented PspA families 1 and 2. Capsular serotypes were generally not exclusively associated with certain PspA families, although some capsular types showed a much higher proportion of either PspA1 or PspA2. A PspA-containing vaccine would potentially provide high coverage against pneumococcal infectious diseases because it would be cross-protective versus invasive disease with the majority of pneumococci infecting children and adults.

Nanogel-based PspA intranasal vaccine prevents invasive disease and nasal colonization by Streptococcus pneumoniae

To establish a safer and more effective vaccine against pneumococcal respiratory infections, current knowledge regarding the antigens common among pneumococcal strains and improvements to the system for delivering these antigens across the mucosal barrier must be integrated. We developed a pneumococcal vaccine that combines the advantages of pneumococcal surface protein A (PspA) with a nontoxic intranasal vaccine delivery system based on a nanometer-sized hydrogel (nanogel) consisting of a cationic cholesteryl group-bearing pullulan (cCHP). The efficacy of the nanogel-based PspA nasal vaccine (cCHP-PspA) was tested in murine pneumococcal airway infection models. Intranasal vaccination with cCHP-PspA provided protective immunity against lethal challenge with Streptococcus pneumoniae Xen10, reduced colonization and invasion by bacteria in the upper and lower respiratory tracts, and induced systemic and nasal mucosal Th17 responses, high levels of PspA-specific serum immunoglobulin G (IgG), and nasal and bronchial IgA antibody responses. Moreover, there was no sign of PspA delivery by nanogel to either the olfactory bulbs or the central nervous system after intranasal administration. These results demonstrate the effectiveness and safety of the nanogel-based PspA nasal vaccine system as a universal mucosal vaccine against pneumococcal respiratory infection.

Pneumococcal surface protein A inhibits complement deposition on the pneumococcal surface by competing with the binding of C-reactive protein to cell-surface phosphocholine

In the presence of normal serum, complement component C3 is deposited on pneumococci primarily via the classical pathway. Pneumococcal surface protein A (PspA), a major virulence factor of pneumococci, effectively inhibits C3 deposition. PspA's C terminus has a choline-binding domain that anchors PspA to the phosphocholine (PC) moieties on the pneumococcal surface. C-reactive protein (CRP), another important host defense molecule, also binds to PC, and CRP binding to pneumococci enhances complement C3 deposition through the classical pathway. Using flow cytometry of PspA(+) and PspA(-) strains, we observed that the absence of PspA led to exposure of PC, enhanced the surface binding of CRP, and increased the deposition of C3. Moreover, when the PspA(-) mutant was incubated with a pneumococcal eluate containing native PspA, there was decreased deposition of CRP and C3 on the pneumococcal surface compared with incubation with an eluate from a PspA(-) strain. This inhibition was not observed when a recombinant PspA fragment, which lacks the choline-binding region of PspA, was added to the PspA(-) mutant. Also, there was much greater C3 deposition onto the PspA(-) pneumococcus when exposed to normal mouse serum from wild-type mice as compared with that from CRP knockout mice. Furthermore, when CRP knockout mouse serum was replenished with CRP, there was a dose-dependent increase in C3 deposition. The combined data reveal a novel mechanism of complement inhibition by a bacterial protein: inhibition of CRP surface binding and, thus, diminution of CRP-mediated complement deposition.

Characterization of the antibody response elicited by immunization with pneumococcal surface protein A (PspA) as recombinant protein or DNA vaccine and analysis of protection against an intranasal lethal challenge with Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is an important candidate for a vaccine against pneumococcal infections. DNA vaccines expressing PspA were shown to protect mice against intraperitoneal and colonization challenge models in mice. We now show that a DNA vaccine expressing PspA from clade 4 (pSec-pspA4Pro) is also able to elicit protection against an intranasal lethal challenge model at levels similar to the recombinant protein PspA4Pro adjuvanted with alum. PspA4Pro + alum induced an IgG response characterized by a high IgG1/IgG2a ratio, leading to a lack of binding of anti-PspA IgG2a antibodies to intact pneumococci in vitro, which is in contrast to the response elicited by pSec-pspA4Pro. Epitopes recognized by the sera were mapped and antibodies induced by immunization with PspA4Pro + alum showed positive reaction with several synthetic peptides, mostly located in the first half of the protein. On the other hand, antibodies induced by the DNA vaccine showed reactivity with only two peptides. Though both strategies were protective against the intranasal lethal challenge model, the elicited humoral responses differ significantly, with the detection of important differences in the Fc (IgG1/IgG2a ratios) and Fab (recognized epitopes) regions of the induced antibodies.

Determination of phenotypes and pneumococcal surface protein A family types of Streptococcus pneumoniae from Malaysian healthy children

BACKGROUND

There is limited information about pneumococcal carriage among healthy children in Malaysia. Therefore, this study was conducted to determine the prevalence rate, serotype distribution, susceptibility pattern, and pneumococcal surface protein A (PspA) family types of Streptococcus pneumoniae isolates in the nasal carriage of children 5 years old or younger in three day care centers in Kuala Lumpur, Malaysia.

METHODS

Nasal swabs were collected from 195 healthy children, age 5 years or younger, from June to December 2010. S pneumoniae was identified by phenotypic and genotypic methods. The serotyping was performed using Pneumotest kit (Statens Serum Institut, Copenhagen, Denmark) and the susceptibility pattern was determined by using the E-test method (AB Biodisk, Solna, Sweden). PspA family typing was done using polymerase chain reaction.

RESULTS

S pneumoniae was found in the nasal carriage of 35.4% of children (69 of 195) and penicillin resistance was found in 23.2% (16 of 69). Among the 69 isolates, multidrug-resistant S pneumoniae (MDRSP) was present in 20.3%. All 16 penicillin-resistant S pneumoniae (PRSP) isolates were resistant to erythromycin and 14 PRSPs (87.5%) were resistant to co-trimoxazole. The six most common serotypes were 6A, 23F, 19A, 6B, 19F, and 15C, which were found in 87% of all isolates. Of the 69 isolates, 24.6% belonged to PspA family 1, 71.0% to PspA family 2, and 4.3% to PspA family 3.

CONCLUSION

Twenty-eight of the isolates (40.6%) belonged to serotypes included in the pneumococcal polysaccharide vaccines (PCV) 7 and 10, whereas 48 (69.5%) were included in PCV13. The high rate of PRSP and MDRSP supports the need for continuing surveillance of pneumococcal carriage. The major PspA families were 1 and 2 (95.7%), thus making them suitable candidates for future vaccines.

PspA family distribution, unlike capsular serotype, remains unaltered following introduction of the heptavalent pneumococcal conjugate vaccine

Pneumococcal conjugate vaccines (PCVs) are recommended for the prevention of invasive pneumococcal disease (IPD) in young children. Since the introduction of the heptavalent pneumococcal vaccine (PCV7) in 2000, IPD caused by serotypes in the vaccine has almost been eliminated, and previously uncommon capsular serotypes now cause most cases of pediatric IPD in the United States. One way to protect against these strains would be to add cross-reactive protein antigens to new vaccines. One such protein is pneumococcal surface protein A (PspA). Prior to 2000, PspA families 1 and 2 were expressed by 94% of isolates. Because PCV7 vaccine pressure has resulted in IPD caused by capsular serotypes that were previously uncommon and unstudied for PspA expression, it was possible that many of the new strains expressed different PspA antigens or even lacked PspA. Of 157 pediatric invasive pneumococcal isolates collected at a large pediatric hospital in Alabama between 2002 and 2010, only 60.5% had capsular serotypes included in PCV13, which came into general use in Alabama after our strains were collected. These isolates included 17 serotypes that were not covered by PCV13. Nonetheless, pneumococcal capsular serotype replacement was not associated with changes in PspA expression; 96% of strains in this collection expressed PspA family 1 or 2. Continued surveillance will be critical to vaccine strategies to further reduce IPD.

Contribution of serotype and genetic background to virulence of serotype 3 and serogroup 11 pneumococcal isolates

The capsular serotype has long been associated with the virulence of Streptococcus pneumoniae. Here we present an in-depth study of phenotypic and genetic differences between serotype 3 and serogroup 11 S. pneumoniae clinical isolates from both the general and indigenous populations of Australia. Both serotypes/groups included clonally unrelated strains with differences in well-known polymorphic virulence genes, such as nanA and pspA, as demonstrated by multilocus sequence typing and Western blot analysis. Nonetheless, the serotype 3 strains were consistently and significantly more virulent in mice than the serogroup 11 strains. Despite extensive genomic analysis, noncapsular genes common to one serotype/group but not the other were not identified. Nevertheless, following the conversion of a serotype 11A isolate to serotype 3 and subsequent analysis in an intranasal infection model, it was evident that both capsular and noncapsular factors determine the virulence phenotype in mice. However, it appears that these noncapsular factors vary from strain to strain.

Lactic acid bacteria in the prevention of pneumococcal respiratory infection: future opportunities and challenges

Lactic acid bacteria (LAB) are technologically and commercially important and have various beneficial effects on human health. Several studies have demonstrated that certain LAB strains can exert their beneficial effect on the host through their immunomudulatory activity. Although most research concerning LAB-mediated enhanced immune protection is focused on gastrointestinal tract pathogens, recent studies have centered on whether these immunobiotics might sufficiently stimulate the common mucosal immune system to provide protection to other mucosal sites as well. In this sense, LAB have been used for the development of probiotic foods with the ability to stimulate respiratory immunity, which would increase resistance to infections, even in immunocompromised hosts. On the other hand, the advances in the molecular biology of LAB have enabled the development of recombinant strains expressing antigens from respiratory pathogens that have proved effective to induce protective immunity. In this review we examine the current scientific literature concerning the use of LAB strains to prevent respiratory infections. In particular, we have focused on the works that deal with the capacity of probiotic and recombinant LAB to improve the immune response against Streptococcus pneumoniae. Research from the last decade demonstrates that LAB represent a promising resource for the development of prevention strategies against respiratory infections that could be effective tools for medical application.

Expansion and evolution of the Streptococcus pneumoniae Spain9V-ST156 clonal complex in Poland

In this study, we analyzed 118 penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) isolates (MICs, >or=0.12 microg/ml) recovered in Poland in 2003 to 2005 from patients with respiratory tract diseases and invasive infections. Seven different serotypes (14, 9V, 23F, 19F, 6B, 19A, and 6A, in order of descending frequency), seven alleles of the murM gene (murMA, murMB6, and the new murMB12 to -16 alleles), and 31 multilocus sequence types (STs) were observed. The vast majority of the PNSP isolates (90.7%) belonged to the international multiresistant clones, and among these, the Spain(9V)-ST156 clonal complex was the most prevalent (56 isolates) and was significantly overrepresented in invasive infections. The clone has been evolving rapidly, as demonstrated by the observed number of STs, the diversity in multiple-locus variable-number-tandem-repeat analysis (MLVA) types, and the polymorphism of pbp and pspA genes (coding for penicillin-binding proteins and the pneumococcal surface protein A, respectively). The presence and structure of the rlrA islet (encoding the pneumococcal pilus) were very well conserved. The Spain(9V)-ST156 clonal complex has been largely responsible for a decreasing susceptibility to penicillin among pneumococci in Poland in recent years, in spite of a relatively moderate antimicrobial use.

Interaction of pneumococcal histidine triad proteins with human complement

The pneumococcal histidine triad (Pht) proteins PhtA, PhtB, PhtD, and PhtE form a group of conserved pneumococcal surface proteins. Humans produce antibodies to Pht proteins upon exposure to pneumococcus, and immunization of mice has provided protective immunity against sepsis and pneumonia and reduced nasopharyngeal colonization. Pht proteins are candidates for inclusion in multicomponent pneumococcal protein vaccines. Their biological function in pneumococcal infections is not clear, but a role in complement inhibition has been suggested. We measured complement deposition on wild-type and Pht mutant strains in four genetic backgrounds: Streptococcus pneumoniae D39 (serotype 2) and R36A (unencapsulated derivative of D39) and strains of serotypes 3, 4, and 19F. PspA and PspC single and double mutants were compared to the wild-type and Pht-deficient D39 strains. Factor H binding was measured to bacterial cells, lysates, and protein antigens. Deletion of all four Pht proteins (Pht(-)) resulted in increased C3 deposition on the serotype 4 strain but not on the other strains. Pht antigens did not bind factor H, and deletion of Pht proteins did not affect factor H binding by bacterial lysates. The Pht(-) mutant serotype 4 strain bound slightly less factor H than the wild-type strain when binding was measured by flow cytometry. Pht proteins may play a role in immune evasion, but the mechanism of function is unlikely to be mediated by factor H binding. The relative contribution of Pht proteins to the inhibition of complement deposition is likely to be affected by the presence of other pneumococcal proteins and to depend on the genetic background.

Diversity of pneumococcal surface protein A (PspA) among prevalent clones in Spain

BACKGROUND

PspA is recognized as a major pneumococcal virulence factor and a possible vaccine candidate. The aim of this study was to analyze the PspA family and clade distribution among 112 Spanish pneumococci representatives of dominant clones among patients with invasive disease (n = 66) and nasopharyngeal healthy carriage in children (n = 46).

RESULTS

PspA family 2 was predominant among invasive (63.6%) and carriage (54.3%) pneumococcal isolates. No PspA family 3 isolates were detected and only one strain was PspA negative. Although four clonal complexes contained strains of different clades, a clear association between clade and multi locus sequence typing results was found. Clades 1, 3 and 4 were associated with a wide variety of sequence types (ST) related to multiresistant and antibiotic-susceptible worldwide-disseminated clones. Clade 1 was associated with Spain 6B-ST90, Spain 14-ST18, Colombia 5-ST289, Sweden 1-ST306, Denmark 14-ST230 and Sweden 1-ST304 clones. Clade 3 was associated with Spain 23F-ST81, Spain 9V-ST156, Tennessee 14-ST67, Netherlands 3-ST180 and Netherlands 7F-ST191 clones. Clade 4 was related to Sweden 15A-ST63, Netherlands 18C-ST113 and Greece 21-ST193 clones. In contrast, PspA clade was not related to serotype, age or clinical origin of the isolates.

CONCLUSION

PspA clades were associated with genotypes. PspA family 2 and family 1 were dominant among major Spanish pneumococcal clones isolated from patients with invasive disease and nasopharyngeal carriage in children.

Streptococcus pneumoniaeProtein Vaccine Candidates: Properties, Activities and Animal Studies

Streptococcus pneumoniae is a causative agent for community acquired pneumonia, bacteremia, acute otitis media, and meningitis. Recent emergence of multi-drug resistant clinical isolates prompts the need of effective vaccine for the prevention of disease. The licensed polysaccharide-based pneumococcal vaccines only elicit protective antibodies against the infection of serotypes that are included in the vaccine. To broaden the protection, the use of pneumococcal proteins will be a feasible and preferable alternative. This communication provides a review on the biochemical properties of these protein candidates, their immunization results in animal studies, and perspectives on the development of protein-based pneumococcal vaccine.

Development of antibodies to PspA families 1 and 2 in children after exposure to Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is an important virulence factor of Streptococcus pneumoniae. PspA exists as two major families, which include variable but serologically cross-reactive proteins. Previous studies with a family 1 PspA antigen suggested that children develop low concentrations of anti-PspA after pneumococcal carriage or infection. In this study, antibody to PspA families 1 and 2 was measured by an enzyme immunoassay of the serum and saliva of children with a history of culture-proven pneumococcal colonization and/or acute otitis media and in the serum and saliva of adults. The PspA families of the pneumococcal strains isolated from children were determined. The majority of the children had high serum and salivary anti-PspA concentrations to the PspA family they had encountered and low concentrations to the other, whereas adults had high antibody concentrations to both PspA families, both in serum and in saliva. The results suggest that children have a relatively family-specific antibody response to the PspA family they have been exposed to and that any PspA vaccine for children should contain members of both major PspA families.

Distribution of pneumococcal surface protein A families 1 and 2 among Streptococcus pneumoniae isolates from children in finland who had acute otitis media or were nasopharyngeal carriers

PspA is a structurally variable surface protein important to the virulence of pneumococci. PspAs are serologically cross-reactive and exist as two major families. In this study, we determined the distribution of PspA families 1 and 2 among pneumococcal strains isolated from the middle ear fluid (MEF) of children with acute otitis media and from nasopharyngeal specimens of children with pneumococcal carriage. We characterized the association between the two PspA families, capsular serotypes, and multilocus sequence types (STs) of the pneumococcal isolates. MEF isolates (n = 201) of 109 patients and nasopharyngeal isolates (n = 173) of 49 children were PspA family typed by whole-cell enzyme immunoassay (EIA). Genetic typing (PCR) of PspA family was done for 60 isolates to confirm EIA typing results. The prevalences of PspA families 1 and 2 were similar among pneumococci isolated from MEF (51% and 45%, respectively) and nasopharyngeal specimens (48% each). Isolates of certain capsule types as well as isolates of certain STs showed statistical associations with either family 1 or family 2 PspA. Pneumococci from seven children with multiple pneumococcal isolates appeared to express serologically different PspA families in different isolates of the same serotype; in three of the children the STs of the isolates were the same, suggesting that antigenic changes in the PspA expressed may have taken place. The majority of the isolates (97%) belonged to either PspA family 1 or family 2, suggesting that a combination including the two main PspA families would make a good vaccine candidate.

Recognition of pneumococcal isolates by antisera raised against PspA fragments from different clades

Pneumococcal surface protein A (PspA) is an important vaccine candidate against pneumococcal infections, capable of inducing protection in different animal models. Based on its structural diversity, it has been suggested that a PspA-based vaccine should contain at least one fragment from each of the two major families (family 1, comprising clades 1 and 2, and family 2, comprising clades 3, 4 and 5) in order to elicit broad protection. This study analysed the recognition of a panel of 35 pneumococcal isolates bearing different PspAs by antisera raised against the N-terminal regions of PspA clades 1 to 5. The antiserum to PspA clade 4 was found to show the broadest cross-reactivity, being able to recognize pneumococcal strains containing PspAs of all clades in both families. The cross-reactivity of antibodies elicited against a PspA hybrid including the N-terminal region of clade 1 fused to a shorter and more divergent fragment (clade-defining region, or CDR) of clade 4 (PspA1–4) was also tested, and revealed a strong recognition of isolates containing clades 1, 4 and 5, and weaker reactions with clades 2 and 3. The analysis of serum reactivity against different PspA regions further revealed that the complete N-terminal region rather than just the CDR should be included in an anti-pneumococcal vaccine. A PspA-based vaccine is thus proposed to be composed of the whole N-terminal region of clades 1 and 4, which could also be expressed as a hybrid protein.

Vaccine-induced human antibodies to PspA augment complement C3 deposition on Streptococcus pneumoniae

Pneumococcal surface protein (PspA) is a virulence factor expressed by all clinical isolates of Streptococcus pneumoniae. PspAs are variable in structure and have been grouped into clades and cross-reacting families based on sequence similarities and immunologic cross-reactivity. At least 98% of PspAs are found in PspA families 1 or 2. PspA has been shown to interfere with complement deposition on pneumococci, thus reducing opsonization and clearance of bacteria by the host immune system. Prior studies using pooled human sera have shown that PspA interferes with C3 deposition on a single strain of S. pneumoniae, WU2, and that mouse antibody to PspA can enhance the deposition of C3 on WU2. The present studies have demonstrated that these previous findings are representative of most normal human sera and each of seven different strains of S. pneumoniae. It was observed that PspAs of PspA families 1 and 2 could inhibit C3 deposition in the presence of immunoglobulin present in all but 3 of 22 normal human sera. These studies have also demonstrated that rabbit and human antibody to PspA can enhance the deposition of C3 on pneumococci expressing either family 1 or 2 PspAs and either capsular types 2, 3, or 11. A vaccine candidate that can elicit immunity that neutralizes or compensates for S. pneumoniae's ability to thwart host immunity would be of value.

Fusion proteins containing family 1 and family 2 PspA fragments elicit protection against Streptococcus pneumoniae that correlates with antibody-mediated enhancement of complement deposition

PspA is an important pneumococcal vaccine candidate that is capable of inducing protection in different animal models. Because of its structural diversity, a PspA-based vaccine should contain at least one fragment from each of the two major families (1 and 2) in order to elicit broader protection. In the present work, we have tested the potential of PspA hybrids containing fused portions of family 1 and 2 (PspA1ABC-4B and PspA1ABC-3AB) PspA fragments to induce protection against pneumococci bearing distinct PspA fragments. Sera from mice immunized with these hybrid PspA fragments were able to increase C3 deposition on pneumococci bearing PspA fragments from both families, in contrast with sera made against the PspA family 1 (PspA1ABC) and PspA family 2 (PspA3ABC) fragments, which were effective only within the same family. Although PspA hybrids were able to extend protection against pneumococcal infection with strains bearing diverse PspA fragments, the immunity elicited by family 2 was clade dependent, suggesting that PspA fragments from family 2 clades 3 and 4 should both be included in a comprehensive PspA vaccine. These results indicate that PspA fusion proteins constitute an efficient immunization strategy for future PspA-based antipneumococcal vaccines since they are able to extend protection provided by a protein derived from a single transcript.

Pneumococcal surface protein A family types of Streptococcus pneumoniae from community-acquired pneumonia patients in Japan

We assessed pneumococcal surface protein A (PspA) family types of 141 isolates of Streptococcus pneumoniae from community-acquired pneumonia patients in Japan. Families 1 and 2 were expressed in 78 (55.3%) and 58 (41.1%) isolates, respectively. Five isolates were not typed either as family 1 or 2. PspA family types were not associated with age, sex, or pneumonia severity. Penicillin-resistant S. pneumoniae was more likely to belong to family 2 whereas organisms highly resistant to erythromycin and positive for ermB were more prevalent in family 1. The association of PspA type with antimicrobial resistance was possibly affected by prevalent serotypes or resistance clones. It would therefore be necessary to include both family 1 and 2 proteins in a PspA-containing vaccine to cover the major PspA families and to reduce antimicrobial resistance.

Genetic diversity of PspA types among nasopharyngeal isolates collected during an ongoing surveillance study of children in Brazil

Pneumococcal surface protein A (PspA) has been considered a potential candidate for human vaccines because of its serotype-independent protective immunity. Nasopharyngeal (NP) pneumococcal colonization is highly prevalent in infants and precedes the invasive disease. Thus, prevention of NP colonization may reduce the burden of pneumococcal disease in children. Scarce information focusing on PspA from pneumococcal carriage in humans is available. We examined the genetic diversity of PspA from NP isolates obtained during an ongoing pneumococcal surveillance study with children. PspA families and clades of 183 community-acquired Streptococcus pneumoniae NP isolates from healthy children (n = 97) and children with respiratory tract infections (n = 48), pneumonia (n = 33), or meningitis (n = 5) were investigated. Overall, 79.8% (n = 146) of the pneumococcal isolates were classified as PspA family 1 (35.5%) and family 2 (44.3%), whereas 20.2% of the isolates could not be typed. The distribution of PspA families and clades did not differ significantly according to the clinical status of the children. A dendrogram comparing the genetic relationship between the amino acid sequences of the clade-defining region of PspA from NP strains together with 24 invasive reference strains (GenBank) closely reproduced the profile of the families and clades previously reported for pneumococcal invasive strains. These findings strengthen the idea that the use of PspA as a vaccine antigen may protect children against carriage as well as invasive pneumococcal disease.

Multilocus sequence types, serotypes, and variants of the surface antigen PspA in Streptococcus pneumoniae isolates from meningitis patients in Poland

Meningitis caused by Streptococcus pneumoniae represents an important factor of morbidity and mortality in humans. In a significant number of cases, this disease is associated with specific clones of the organism, the so-called invasive pneumococcal clones. The aim of the study was to analyze 156 S. pneumoniae isolates identified as etiological agents of meningitis in Poland in the years 1997 through 2002. The isolates were characterized by multilocus sequence typing (MLST), and the results were compared with those obtained by pulsed-field gel electrophoresis (PFGE) and with the MLST data on invasive pneumococci from other countries. Eighty-nine different sequence types were found in the group of isolates, 50 of which had been known before including 19 of the major invasive clones. However, a significant fraction of the isolates possessed novel combinations of known and new MLST alleles. The majority of penicillin-nonsusceptible isolates belonged to the group of international multiresistant clones (Spain(23F)-1, Spain(6B)-2, Spain(9V)-3, Poland(23F)-16, and Poland(6B)-20), which underlined the importance of these in the dissemination of antimicrobial resistance. The results of the MLST analysis correlated well with the PFGE data, thus again demonstrating good congruence between the two typing methods for S. pneumoniae. The majority of the isolates (95.5%) belonged to families 1 or 2 of the surface protein PspA, confirming its potential usefulness as the vaccine antigen candidate.

CCL5 Modulates Pneumococcal Immunity and Carriage

Understanding the requirements for protection against pneumococcal carriage and pneumonia will greatly benefit efforts in controlling these diseases. Recently, it has been shown that genetic polymorphisms can result in diminished expression of CCL5, which results in increased susceptibility to and progression of infectious diseases. We show that CCL5, together with Th cytokine mRNA expression, is temporally up-regulated during pneumococcal carriage. To determine the contribution of CCL5 to pneumococcal surface antigen A-specific humoral and cellular pneumococcal immunity, mice were treated with anti-CCL5 or control Abs before and during Streptococcus pneumoniae strain EF3030-challenge for the initiation of carriage. CCL5 blockade resulted in a decrease of CD4(+) and CD8(+) T cells as well as CD11b(+) cells in the spleen, cervical lymph node, lung, and nasopharyngeal associated lymphoid tissue during the recognition phase of the pneumococcal adaptive immune response. CCL5 blockade significantly reduced the Ag-specific IgG2a and IgG1 Abs in serum and IgA Ab levels in nasal washes. These decreases also corresponded to reductions in Ag-specific T cell (mucosal and systemic) responses. CCL5 inhibition resulted in decreasing the quantity of IL-4- and IFN-gamma-secreting CD4(+) T cells and increasing the number of Ag-specific IL-10-producing CD4(+) T cells; these changes combined also corresponded with the transition from pneumococcal carriage to lethal pneumonia. These data suggest that CCL5 is an essential factor for the induction and maintenance of protective pneumococcal immunity.

Pneumococcal surface protein A (PspA) family distribution among clinical isolates from adults over 50 years of age collected in seven countries

The pneumococcal surface protein PspA, a cell-wall-associated surface protein, is a promising component for pneumococcal vaccines. In this study, the distribution of the PspA family was determined in a panel of invasive and clinically important pneumococcal isolates from adults over 50 years of age, collected between 1995 and 2002. One thousand eight hundred and forty-seven recent isolates from invasive pneumococcal disease were obtained from seven Western countries, together with clinical data. An ELISA-based serological method was standardized in order to determine the PspA family and clade distribution. Molecular tests were used when isolates were non-typable by ELISA (PspA family typing by PCR). Only 42 (2·3 %) isolates were non-typable by ELISA and PspA family typing by PCR was performed. Finally, 3 isolates were considered as non-pneumococcal and 1844 were classified as follows: 749 (40·6 %) were PspA family 1, 1078 (58·5 %) were PspA family 2, 13 (0·7 %) were PspA family 1 and 2 and 4 (0·2 %) remained non-typable. The cross-reactivity of antibodies to PspAs of different clades was confirmed. In conclusion, inclusion of PspA family 1 and family 2 in future pneumococcal vaccines would ensure broad coverage of pneumococcal strains infecting people over 50 years of age.

Emergence of W135 meningococcal meningitis in Ghana

Neisseria meningitidis serogroup W135, well known for a long time as a cause of isolated cases of meningococcal meningitis, has recently increasingly been associated with disease outbreaks of considerable magnitude. Burkina Faso was hit by W135 epidemics in the dry seasons of 2002-2004, but only four W135 meningitis cases were recorded between February 2003 and March 2004 in adjoining Ghana. This reconfirms previous findings that bottlenecks exist in the spreading of new epidemic N. meningitidis clones within the meningitis belt of sub-Saharan Africa. Of the four Ghanaian W135 meningitis patients one died and three survived, of whom one had profound neurosensory hearing loss and speech impairment. All four disease isolates were sensitive to penicillin G, chloramphenicol, ciprofloxacin and cefotaxime and had the multi-locus sequence type (ST) 11, which is the major ST of the ET-37 clonal complex. Pulsed-field gel electrophoresis (PFGE) profiles of the Ghanaian disease isolates and recent epidemic isolates from Burkina Faso were largely identical. We conducted meningococcal colonization surveys in the home communities of three of the patients and in the Kassena Nankana District located at the border to Burkina Faso. W135 carriage rates ranged between 0% and 17.5%. When three consecutive surveys were conducted in the patient community with the highest carrier rate, persistence of W135 colonization over a period of 1 year was observed. Differences in PFGE profiles of carrier isolates taken at different times in the same patient community were indicative of rapid microevolution of the W135 bacteria, emphasizing the need for innovative fine typing methods to reveal the relationship between W135 isolates.