The role of Streptococcus pneumoniae virulence factors in host respiratory colonization and disease

The microbiological characteristics and diagnosis of Streptococcus pneumoniae infection in the conjugate vaccine era

Two pneumococcal conjugate vaccines, PCV15 and PCV20, were licensed in June 2021. PCV15 includes two additional serotypes (22F, 33F) beyond those in PCV13, while PCV20 adds seven more (8, 10A, 11A, 12F, 15B, 22F, 33F), covering approximately 30% of invasive pneumococcal disease (IPD) cases in adults. In June 2023, the US CDC's Advisory Committee on Immunization Practices (ACIP) recommended either PCV15 or PCV20 for all children aged < 5 years and children aged 2‒18 years with risk conditions. In June 2024, the FDA approved PCV21 for adults ≥ 18 years. In October 2024, ACIP recommended either PCV20 or PCV21 alone or PCV15 with PPSV23 for adults ≥ 50 years or 19-49 years with risk conditions. These advancements highlight the evolving landscape of pneumococcal vaccination. This review examines the molecular epidemiology of pneumococcal infections, advancements in diagnostic methods, and the anticipated public health impact of these vaccines in reducing pneumococcal disease burden.

Altered cytokine release of airway epithelial cells in vitro by combinations of respiratory syncytial virus, Streptococcus pneumoniae, Printex 90 and diesel exhaust particles

Air pollution exposure has been linked to an increased severity of respiratory infections. Studying the cellular mechanisms behind a potential interaction between biological infectious agents, like viruses or bacteria, and the chemical constituent of air pollution could provide more understanding of this finding. In vitro models allow assessment of the mechanisms leading to such increased severity of respiratory infections. The response of primary respiratory bronchial epithelial cells was investigated after combined exposure to biological agents (Respiratory Syncytial Virus (RSV), the bacterium Streptococcus pneumoniae), and chemical agents (Printex 90 or diesel exhaust particles (DEP)). Multiple combinations of exposures to these agents were tested and the effect on cell viability and cytotoxicity were assessed. The secretion levels of 24 pro- and anti-inflammatory cytokines were assessed at levels that did not cause cytotoxicity. Infection with RSV resulted in decreased metabolic activity and an increase in cytokine levels compared to the other exposures. Exposures to the bacterial and chemical agents, in addition to an RSV infection, resulted in a further increase in cytokine levels. We found a cluster of cytokines that responded similarly to the performed exposures which were CXCR3 ligands CXCL9, CXCL10 and CXCL11 and CCR5 ligand CCL5. Even though the data suggests that combined exposures result in a further increase of cytokine levels, this was not confirmed by statistical analysis. Together, this information may help to understand the cellular effects of combined exposure in an in vitro setting and the biological responses to these exposures in vivo.

The global transcriptional regulator MgaSpn affects the virulence of Streptococcus pneumoniae by regulating PcpA

The global transcriptional regulator MgaSpn is a significant virulence factor of Streptococcus pneumoniae. In our previous study, we found that MgaSpn is a regulator of bacterial virulence by modulating the levels of phosphorylcholine (ChoP) and capsular polysaccharides (CPS) on the surface of S. pneumoniae. Here, we report for the first time that pcpA expression was significantly increased in mgaSpn deletion strains and significantly decreased when mgaSpn was overexpressed. Electrophoretic mobility-shift and DNase I footprinting assays confirmed that MgaSpn interacts with the pcpA promoter (PpcpA) at two specific binding sites. Virulence experiments demonstrated that the interaction between MgaSpn and PcpA is necessary for pneumococcal colonization and invasive infection. Western blot analysis indicated that iron concentration can influences the regulation of PcpA expression via MgaSpn. In summary, these results revealed that MgaSpn regulates PcpA and plays a significant role in pneumococcal pathogenesis.

Serotype specific pneumococcal vaccine effectiveness in children with sickle cell disease: A two-decade analysis

OBJECTIVES

Sickle cell disease (SCD) is the most common genetic hematologic disease globally and children with SCD are at increased risk for pneumococcal disease.

METHODS

We utilized data from population-based enhanced surveillance for invasive pneumococcal disease (IPD) in children <18 years of age in Massachusetts from 2002 to 2020. We calculated incidence rates (IR) among children with SCD using bootstrapping resampling and incidence rate ratios (IRR) for pre- and post-PCV13 periods. Vaccine effectiveness (VE) was calculated as 100*(1-IRR), and PCV13 vaccine failure probability was predicted using a random forest model.

RESULTS

Children with SCD had higher IR during both pre-/post-PCV13 periods compared with otherwise healthy children 240.0/100,000 versus 4.6/100,000 in pre-PCV13 period (2002-2009); 172.7/100,000 versus 1.9/100,000 in post-PCV13 period (2011-2020), respectively. After widespread use of PCV7 for a decade, a modest reduction of 28.1 % (95% CI 25.9-37.2%) in the incidence of overall IPD during the post-PCV13 period was observed in children with SCD, whereas a more substantial 59.5% (96% CI 57.8-61.4%) reduction was observed in otherwise healthy children. There was a 60.8% (95% CI 55.2%-NA) reduction in the incidence of VST13 IPD in children with SCD and an 83.0% (95% CI 80.67-85.63%) reduction in children without underlying health condition. Overall, 61.1% of the remaining IPD among children with SCD were due to non-PCV13 serotypes (8, 10A, 15A,15B, 22F, 23B), many of which are included in expanded valency vaccines.

CONCLUSION

Children with SCD continue to have higher rates of IPD compared with otherwise healthy children despite vaccination. Majority of the remaining disease is due to serotypes not included in vaccine formulations that have been used for the last two decades. Our study highlights the potential value of expanded valency vaccines and importance of risk-based vaccination strategies tailored for this vulnerable population.

Evaluation of Fourier-Transform Infrared Spectroscopy with IR Biotyper® system for Streptococcus pneumoniae serotyping

PURPOSE

Streptococcus pneumoniae is an important human pathogen and its virulence is centered on the expression of a polysaccharide capsule. Serotyping pneumococci has clinical and epidemiological relevance. As the gold standard (Quellung reaction) is expensive and somehow laborious, alternative methodologies for timely serotyping are desirable. We aimed to evaluate IR Biotyper® (Bruker), which is based on FT-IRS, as a tool for serotyping S. pneumoniae by customizing a classifier focusing on PCV15 serotypes.

METHODS

Initially, we evaluated the Pneumococci serogrouper (Bruker) included in the IR Biotyper® software (v.4.0) using 188 retrospective isolates of S. pneumoniae previously serotyped by the gold standard. Lately, these isolates were used to construct (n = 83) and validate (n = 105) the PCV15-Classifier. Overall, 1246 spectra were obtained to create a classification model using artificial neural network (ANN) machine learning in 400 cycles. Finally, prospective S. pneumoniae (n = 61), recovered from patients attended at hospitals in South Brazil, were used for a "real-life" evaluation of both classifiers.

RESULTS

Agreement was higher when using PCV15-Classifier instead of Pneumococci serogrouper (Bruker) among both, retrospective (86.7% versus 68.1%; p = 0.0004) and prospective isolates (75.4% versus 70.5%; p = 0.54), highlighting (i) its better performance for epidemiologically relevant serotypes, such as 3, and (ii) its capacity to discriminate between serotypes of serogroup 19 (19F and 19A).

CONCLUSION

Altogether, our results reiterate the usefulness of IR Biotyper® for serotyping S. pneumoniae applying a customized classifier, which can be re-trained whenever needed, following the evolution of serotype distribution.

Quantitative phosphoproteomic reveals that the induction of competence modulates protein phosphorylation in Streptococcus pneumonaie

Competence in the pathogenic bacterium Streptococcus pneumoniae (S. pneumoniae) is a developmental genetic program that is key for natural genetic transformation and consequently bacterial horizontal gene transfer. Phosphoproteomic studies have revealed that protein phosphorylation on serine, threonine and tyrosine residues is a widespread regulatory post-translational modification in bacteria. In this study, we performed quantitative proteomic and phosphoproteomic analyses on S. pneumoniae as a function of competence induction. To calculate peptide abundance ratios between non-competent and competent samples we used dimethyl-tag labeling. Titanium dioxide (TiO2) beads were used for phosphopeptide enrichment and samples were analysed by LC-MS/MS. Our proteome analysis covers approximatively 63 % of the total bacterial protein content, identifying 82 proteins with significantly different abundance ratios, including some not previously linked to competence. 248 phosphopeptides were identified including 47 having different abundance ratios. Notably, the proteins with a change in phosphorylation in competent cells are different from the proteins with a change in expression, highlighting different pathways induced by competence and regulated by phosphorylation. This is the first report that phosphorylation of some proteins is regulated during competence in Streptococcus pneumoniae, a key pathway for the bacteria to evade vaccines or acquire antibiotic resistance. SIGNIFICANCE: S. pneumoniae is a prominent model for the study of competence that governs the development of natural genetic transformation. The latter largely accounts for the spread of antibiotic resistance and vaccine evasion in pneumococcal isolates. Many proteins specifically expressed during competence have been identified and extensively studied. However, the potential contribution of post-translational modifications, and notably phosphorylation, during the development of competence has never been investigated. In this study, we used a quantitative phosphoproteomic approach to determine both the protein expression and the protein phosphorylation patterns. Comparison of these patterns allows to highlight a series of proteins that are differentially phosphorylated in the two conditions. This result opens new avenues to decipher new regulatory pathways induced by competence and that are potentially key for natural genetic transformation. Interfering with theses regulatory pathways could represent a promising strategy to combat antibiotic resistance in the future.

Pneumococcal serotypes and their association with death risk in invasive pneumococcal disease: a systematic review and meta-analysis

Background

Streptococcus pneumoniae and its infections are a global public health concern. Invasive pneumococcal disease accounts for significant mortality in the aged and immunocompromised. Over 100 unique capsular serotypes have been identified, with 80-90% of invasive disease attributable to about 23 serotypes. Pneumococcal serotype influences invasiveness, virulence, carriage, and IPD outcome. Case fatality rates among different pneumococcal serotypes in IPD have been inconsistently reported, prompting the need for a comprehensive meta-analysis. We hypothesized that specific pneumococcal serotypes would be associated with higher case fatality rates and that non-vaccine serotypes may exhibit increased mortality risks over time.

Methods

We conducted a systematic review and meta-analysis of serotype-specific risk of death due to invasive pneumococcal disease (IPD) in the last decade. We calculated the risk ratio (RR) and 95% confidence interval (CI) for each serotype compared with serotype 14 in each study. Pooled risk ratios were computed using random effects size model analysis. We also conducted heterogeneity testing and meta-regression sub-analysis.

Results

In total, 45 eligible studies were included, and 16 were selected for meta-analysis. Study distribution showed a global disparity, with Europe as the major data source. Serotype 31 had the highest case fatality rate (31.4%), indicating a concerning mortality risk associated with this serotype, particularly in immunocompromised patients. Overall, IPD patients with serotypes 3, 6A, 11A, 15A, 19F, and 31 were more likely to die. In contrast, serotypes 1, 5, 7F, and 8 IPD isolates recorded a reduced risk ratio compared to serotype 14. Subgroup analysis showed that vaccine serotypes were associated with a greater risk of death than non-vaccine serotypes, but there were no significant differences in risk estimates between population groups.

Conclusion

The study confirms the stable role of pneumococcal serotype in determining the clinical outcomes of invasive pneumococcal disease. Our findings underscore the importance of serotype-specific surveillance in IPD and call for the reconsideration of current pneumococcal vaccine formulations to address high-risk non-vaccine serotypes. Efforts to build research capacity, especially in low-resource regions such as Africa and South America, are highly recommended.

Transmission of the human respiratory microbiome and antibiotic resistance genes in healthy populations

BACKGROUND

The human microbiome is transmissible between individuals, including pathogens and commensals with metabolic and immune-modulating effects, which could influence susceptibility, severity, and outcomes of both infection and non-infection diseases. However, limited studies of respiratory microbiome transmission within populations have been conducted. Herein, we performed species- and strain-level metagenomic analyses on oropharyngeal (OP) swabs from 1046 healthy urban dwellers across 13 districts, including 111 households with at least two cohabitants, to elucidate the transmission dynamics of the respiratory microbiome within households and communities.

RESULTS

We found that geographic districts accounted for the greatest variation in the OP microbiome, with unrelated individuals from the same district showing greater microbiome similarity and higher strain-sharing rates than those from different districts. Cohabitants, especially spouses and siblings, exhibited similar microbial abundances and shared more strains, with 16.7% (IQR 0.0-33.3%) of strains shared among cohabitants, compared to 0.0% (IQR 0.0-11.1%) in non-cohabiting pairs (p < 0.05). Both respiratory commensals and opportunistic pathogens were shared among cohabitants. In contrast, no evidence of vertical transmission was detected between mother-offspring pairs. Additionally, the OP microbiome contained diverse antibiotic resistance genes (ARGs), with 15.0% linked to mobile genetic elements (MGEs) or plasmids; the flanking sequences of these ARGs were more conserved across species than those of non-MGE-associated ARGs, suggesting horizontal transfer of ARGs among respiratory microorganisms.

CONCLUSIONS

In summary, we characterized the transmissible nature of the OP microbiome and the risk of ARG dissemination among respiratory microorganisms. These findings underscore the role of respiratory microbes and ARGs exchange in shaping the microbiome of healthy populations and emphasize their relevance to public health strategies for respiratory health management. Video Abstract.

Cohort study exploring the association of cerebrospinal fluid metalloprotease levels and Microbiological characteristics to cerebral vasculitis complication in Pneumococcal meningitis

Cerebrovascular complications are frequent in pneumococcal meningitis and are associated with poor functional outcomes. Among these complications, the incidence of cerebral vasculitis (CV) has been increasingly reported, but neither its pathogenesis nor its relationship with cortisone treatment have been conclusively established. We wanted to describe cerebrospinal fluid (CSF) metalloprotease (MMP) levels, which are linked to cerebral damage and vasculitis (MMP-2, MMP-9, and the antagonist TIMP-1), and differences in microbiological serotypes or virulence factors that could be associated to the development of this complication. A prospective multicenter cohort study was performed from January 2019 to August 2022. All adult patients diagnosed with pneumococcal meningitis and for whom CSF samples from the initial lumbar puncture were available were included and followed up for six months after discharge. Streptococcus pneumoniae strains isolated from CSF or blood were assessed including whole genome sequencing and CSF levels of MMP-2, MMP-9, and TIMP-1 were measured. CV developed in three of 21 patients (14.3%). The serotypes of those who developed CV were 3, 9 N, and 35 F, with no microbiological differences with respect to the non-CV group. The CV group had higher CSF levels of MMP-9 (13.2 vs. 9.8 ng/L) and TIMP-1 (699 vs. 318 ng/L), but lower CSF levels of MMP-2 (5689 vs. 10,484 ng/L) compared with the non-CV group. Although no patients with CV died, they had worse clinical outcomes than the non-CV group. CV is a frequent complication of pneumococcal meningitis that may be associated with worse outcomes. No differences in microbiological serotypes or virulence factors were detected. Further analyses should be carried out to confirm whether CSF MMP levels may be markers of CV development.

Bacterial clustering biomaterials as anti-infective therapies

In Nature, bacterial clustering by host-released peptides or nucleic acids is an evolutionarily conserved immune defense strategy employed to prevent adhesion of pathogenic microbes, which is prerequisite for most infections. Synthetic anti-adhesion strategies present as non-lethal means of targeting bacteria and may potentially be used to avoid resistance against antimicrobial therapies. From bacteria-agglutinating biomolecules discovered in nature to synthetic designs involving peptides, cationic polymers and nanoparticles, the modes of actions appear broad and unconsolidated. Herein, we present a critical review and update of the state-of-the-art in synthetic bacteria-clustering designs with proposition of a more streamlined nomenclature and classification. Overall, this review aims to consolidate the conceptual framework in the field of bacterial clustering and highlight its potentials as an avenue for discovering novel antibacterial biomaterials.

Metaviromic and metagenomic study of the pathogens in unexplained pneumonia cases in goats

Goats are an economically important livestock species in China. However, the high mortality rate due to pneumonia represents a significant challenge to the development of intensive goat farms. 10 goat lung tissue samples were collected in this study, and all samples exhibited pneumonia of different severity as determined by lung lesion scoring and histopathological examination. Subsequently, this study employed qRT-PCR to measure the relative expression level of pro-inflammatory cytokines in lung tissue, and conducted metaviromic and metagenomic analyses to elucidate the structure and composition of the pulmonary microbiota, the correlation between the abundance of specific microbes and inflammatory factors, and between microbial abundance and the expression of virulence genes. Metaviromic results indicated that Ungulate tetraparvovirus 4 (83.3 %) had the highest relative abundance in the viral composition. Metagenomic data showed that Mycoplasma (28.2 %) and Streptococcus (24.8 %) are the primary dominant genus in goat pneumonia. Notably, a total of 8 pathogens associated with pneumonia in humans or animals were identified across all samples, including Mycoplasma ovipneumoniae, Streptococcus agalactiae, Streptococcus pneumoniae, Escherichia coli, Bordetella hinzii, Bibersteinia trehalosi, Bordetella pertussis, and Pasteurella multocida, with mixed infections with multiple pathogens are very common in this study. Correlation analysis indicates a significant association between the degree of pathogen co-infection and the severity of pulmonary lesions. Furthermore, Pasteurella multocida showed a significant positive correlation with the expression of IL-6 (P< 0.01). The pneumonia samples also revealed a multitude of virulence factors associated with bacterial pathogenicity including those related to biofilm formation, endotoxin production, bacterial invasion and evasion of host immunity. In conclusion, the present study can provide a reference for clinical pathogen diagnosis of unexplained pneumonia in goats.

Comparative pangenomics of Streptococcus pneumoniae from Malawi: uncovering genetic variability and pathogenicity

Streptococcus pneumoniae is a significant cause of bacterial infections, including pneumonia, meningitis and septicemia, primarily affecting children, the elderly and immunocompromised individuals. This study aimed to elucidate the serotype and lineage distribution and molecular mechanisms underlying pneumococcal invasiveness through a comprehensive pangenomic analysis of 1416 isolates from Malawi. Our analysis comprised 810 isolates from asymptomatic carriers and 606 isolates from patients with bacteraemia or meningitis. We identified 58 serotypes, with serotypes 1, 5 and 12F exhibiting significantly higher prevalence among patients. These serotypes likely exhibit reduced nasopharyngeal colonization and demonstrate rapid dissemination to sterile sites. Notably, these serotypes form a distinct lineage with distinct genomic characteristics, including the absence of V-type ATP synthase. The pangenome analysis revealed two highly conserved surface protein complexes, F-type ATP synthase and SecA1-SecY, which deserve further investigation as potential targets for novel therapeutic interventions.

Captive environments reshape the compositions of carbohydrate active enzymes and virulence factors in wolf gut microbiome

Species in the family Canidae occupy different spatial ecological niches, and some (e.g., wolf) can be kept in zoos. The gut microbiome may differ among various wild and captive canids. Therefore, we compared the gut microbiomes of wild canids (wolf, red fox, and corsac fox) in the Hulun Lake area, captive wolves, and domestic dogs in different regions using metagenomic data. A random forest analysis revealed significant enrichment for bacterial species producing short-chain fatty acids and the thermogenesis pathway (ko04714) in the gut microbiome of wild wolf, potentially providing sufficient energy for adaptation to a wide range of spatial ecological niches. The significantly enriched bacterial species and functional pathways in the gut microbiome of corsac foxes were related to physiological stability and adaptation to arid environments. Alpha diversity of carbohydrate-active enzymes in the gut microbiome was higher in the red fox than in the corsac fox and wild wolf, which may be related to the abundance of plant seeds (containing carbohydrates) in their diets (red foxes inhabit seed-rich willow bosk habitats). However, the influence of host genetic factors cannot be excluded, and further experimental studies are needed to verify the study results. In addition, captive environments drove similarity in carbohydrate-active enzymes (CAZymes) and virulence factors (VFs) in the gut microbiomes of captive wolf and domestic dog, and increased the diversity of CAZymes and VFs in the gut microbiome of captive wolf. Increased VFs diversity may increase the pathogenic potential of the gut microbiome in captive wolves. Therefore, it is necessary to continue monitoring the health status of captive wolves and develop appropriate management strategies.

The enigmatic voyage of pneumococcal carriage: Unraveling the risk factors in pediatric populations -- A scoping review

BACKGROUND

Pneumococcal infections are a major cause of morbidity and mortality globally, especially among children in low- and middle-income countries (LMICs). Although considerable research has been done on the frequency of pneumococcal infections and their risk factors, there are still many unanswered questions. The objective of this study is to offer fresh perspectives through systematic literature review on the shifting prevalence of and associated risk factors for pneumococcal colonization.

METHODS

A systematic search of literature from January 2012 to December 2023 was conducted using PubMed and Scopus, with keywords related to Streptococcus pneumoniae colonization and risk factors, and references were manually screened.

RESULTS

Studies from 41 different countries are included in the evaluation, which focuses on pediatrics patients who are most vulnerable to pneumococcal infections. The most frequent risk variables for pneumococcal colonization were having siblings, daycare centers, passive smoking, household characteristics, age, comorbidities, and vaccination status. The frequency of pneumococcal colonization was greatest among LMICs, which may be related to inadequate pneumococcal vaccination programs, densely populated areas, and a lack of knowledge about basic sanitation and hygiene.

CONCLUSION

The study emphasizes how crucial it is to monitor serotype prevalence to direct vaccination campaigns in these regions. For creating efficient pneumococcal disease prevention and control strategies, it is essential to understand the risk factors connected to pneumococcal colonization. The review highlights the value of vaccination campaigns in lowering the prevalence of pneumococcal illness, to completely understand the relationship between immunization, serotype colonization, and the risk of pneumococcal colonization, more study is required especially in LIC and LMIC region.

Simplified process for preparing native and depolymerized capsular polysaccharides of Streptococcus pneumoniae

Streptococcus pneumoniae is a major pathogen of bacterial pneumonia, meningitis, sepsis, and otitis media. The pathogenicity of this bacterium is largely attributed to its polysaccharide capsule, a protective layer around bacterial cell that enables bacteria to resist against host defense. Capsular polysaccharides (CPSs) of S. pneumoniae have been used as antigens to develop a variety of pneumococcal vaccines against invasive pneumococcal disease (IPD). These vaccines have been proven to be effective in reducing the incidence of IPD cases that are caused by vaccine-covered serotypes at the global scale. A crucial step in the manufacture of pneumococcal polysaccharide and conjugate vaccines is to purify native and depolymerized CPSs to meet strict quality standards in purity and structural integrity. The major impurities comprise proteins, nucleic acids and cell wall polysaccharides (CWPS). Traditionally, the removal of impurities to obtain purified native CPSs involves a complex process of purification, after which purified CPSs need to be further size-reduced to obtain depolymerized CPSs by multi-step approaches. In this study, we streamlined the process of CPS purification, which involves firstly ultrafiltration, followed by one-step acid precipitation, and finally diafiltration to obtain pure native CPSs. Furthermore, hydrolysis using trifluoroacetic acid (TFA) was integrated into the process to obtain purified depolymerized CPSs. The native and depolymerized CPSs produced by this optimized process were comparable to the materials obtained by the traditional approaches in purity and structural integrity, which would meet the quality standards of CPSs for vaccine production in the current edition of the European Pharmacopeia.

Chemical dissection of bacterial virulence

The emergence of antibiotic-resistant bacteria has intensified the need for novel therapeutic strategies targeting bacterial virulence rather than growth or survival. Bacterial virulence involves complex processes that enable pathogens to invade and survive within host cells. Chemical biology has become a powerful tool for dissecting these virulence mechanisms at the molecular level. This review highlights key chemical biology approaches for studying bacterial virulence, focusing on four areas: 1) regulation of virulence, where chemoproteomics has identified small molecule-protein interactions that modulate virulence gene expression; 2) identification of virulence proteins, using techniques like unnatural amino acid incorporation and activity-based protein profiling (ABPP) to uncover proteins involved in infection; 3) post-translational modifications of host proteins, where chemical probes have revealed how bacterial effectors alter host cell processes; and 4) effector-host protein interactions, with methods such as bifunctional unnatural amino acid incorporation facilitating the discovery of key host targets manipulated by bacterial effectors. Collectively, these chemical tools are providing new insights into pathogen-host interactions, offering potential therapeutic avenues that aim to disarm pathogens and combat antibiotic resistance.

Structural analysis of extracellular ATP-independent chaperones of streptococcal species and protein substrate interactions

During infection, bacterial pathogens rely on secreted virulence factors to manipulate the host cell. However, in gram-positive bacteria, the molecular mechanisms underlying the folding and activity of these virulence factors after membrane translocation are not clear. Here, we solved the protein structures of two secreted parvulin and two secreted cyclophilin-like peptidyl-prolyl isomerase (PPIase) ATP-independent chaperones found in gram-positive streptococcal species. The extracellular parvulin-type PPIase, PrsA in Streptococcus pneumoniae and Streptococcus mutans maintain dimeric crystal structures reminiscent of folding catalysts that consist of two domains, a PPIase and foldase domain. Structural comparison of the two cyclophilin-like extracellular chaperones from S. pneumoniae and Streptococcus pyogenes with other cyclophilins demonstrates that this group of cyclophilin-like chaperones has novel structural appendages formed by 9- and 24-residue insertions. Furthermore, we demonstrate that deletion of prsA and slrA genes impairs the secretion of the cholesterol-dependent pore-forming toxin, pneumolysin in S. pneumoniae. Using protein pull-down and biophysical assays, we demonstrate a direct interaction between PrsA and SlrA with Ply. Then, we developed chaperone-assisted folding assays that show that the S. pneumoniae PrsA and SlrA extracellular chaperones accelerate pneumolysin folding. In addition, we demonstrate that SlrA and, for the first time, S. pyogenes PpiA exhibit PPIase activity and can bind the immunosuppressive drug, cyclosporine A. Altogether, these findings suggest a mechanistic role for streptococcal PPIase chaperones in the activity and folding of secreted virulence factors such as pneumolysin.

IMPORTANCE

Streptococcal species are a leading cause of lower respiratory infections that annually affect millions of people worldwide. During infection, streptococcal species secrete a medley of virulence factors that allow the bacteria to colonize and translocate to deeper tissues. In many gram-positive bacteria, virulence factors are secreted from the cytosol across the bacterial membrane in an unfolded state. The bacterial membrane-cell wall interface is exposed to the potentially harsh extracellular environment, making it difficult for native virulence factors to fold before being released into the host. ATP-independent PPIase-type chaperones, PrsA and SlrA, are thought to facilitate folding and stabilization of several unfolded proteins to promote the colonization and spread of streptococci. Here, we present crystal structures of the molecular chaperones of PrsA and SlrA homologs from streptococcal species. We provide evidence that the Streptococcus pyogenes SlrA homolog, PpiA, has PPIase activity and binds to cyclosporine A. In addition, we show that Streptococcus pneumoniae PrsA and SlrA directly interact and fold the cholesterol-dependent pore-forming toxin and critical virulence determinant, pneumolysin.

Retrospective study on the epidemiological characteristics of multi-pathogen infections of hospitalized severe acute respiratory tract infection and influenza-like illness in Xinjiang from January to May 2024

BACKGROUND

Acute respiratory tract infections are very common and can be caused by many pathogens. The aim of this study was to understand the characteristics of multi-pathogen infections of respiratory tract infections during the seasonal changes in winter and spring in Xinjiang.

METHODS

Throat swab samples were collected from 2791 patients with influenza-like illness (ILI) and hospitalized severe acute respiratory tract infection (SARI) in Xinjiang from January 2024 to May 2024 for multi-pathogen detection. Then, the infection frequency of pathogens and their distribution characteristics in different months, genders, regions and case classifications were analyzed.

RESULTS

The positive infection rate of pathogens in 2791 patients was 48.30% (1348/2791). The proportion of patients infected with respiratory pathogens in the 0-9 age group was the highest. Of all pathogens detected, MP was most common in positive patients (22.03%). The highest frequency of multiple infections was SPn. RSV, FluA and FluB were the main infectious pathogens in January and February. The number of RV, HPIV and MP infections showed an increasing trend from January to May. Compared to female patients, male patients are more likely to be infected with ADV and SPn. Compared with hospitalized SARI patients, outpatient and emergency ILI patients were more susceptible to infection with ADV and FluB. However, hospitalized SARI patients were more susceptible to infection with RSV and MP. The positive infected patients mainly came from northern Xinjiang (60.83%). Compared with other regions, the proportion of ADV positive patients in northern Xinjiang was higher.

CONCLUSION

This study revealed the distribution characteristics of pathogen infection in patients with respiratory tract infections in different months, genders, regions and case classifications during the seasonal changes of winter and spring in Xinjiang for the first time, which is helpful to formulate more effective treatment strategies and preventive measures.

CLINICAL TRIAL NUMBER

not applicable.

Synthesis of Fluorinated Glycotope Mimetics Derived from Streptococcus pneumoniae Serotype 8 CPS

Fluorination of carbohydrates is a promising strategy to produce glycomimetics with improved pharmacological properties, such as increased metabolic stability, bioavailability and protein-binding affinity. Fluoroglycans are not only of interest as inhibitors and chemical probes but are increasingly being used to develop potential synthetic vaccine candidates for cancer, HIV and bacterial infections. Despite their attractiveness, the synthesis of fluorinated oligosaccharides is still challenging, emphasizing the need for efficient protocols that allow for the site-specific incorporation of fluorine atoms (especially at late stages of the synthesis). This is particularly true for the development of fully synthetic vaccine candidates, whose (modified) carbohydrate antigen structures (glycotopes) per se comprise multistep synthesis routes. Based on a known minimal protective epitope from the capsular polysaccharide of S. pneumoniae serotype 8, a panel of six novel F-glycotope mimetics was synthesized, equipped with amine linkers for subsequent conjugation to immunogens. Next to the stepwise assembly via fluorinated building blocks, the corresponding 6F-substituted derivatives could be obtained by microwave-assisted, nucleophilic late-stage fluorination of tri- and tetrasaccharidic precursors in high yields. The described synthetic strategy allowed for preparation of the targeted fluorinated oligosaccharides in sufficient quantities for future immunological studies.

Review of the aetiologies of central nervous system infections in Vietnam

Central nervous system (CNS) infections are an important cause of morbidity and mortality in Vietnam, with many studies conducted to determine the aetiology. However, the cause remains unknown in a large proportion of cases. Although a systematic review of the aetiologies of CNS infections was conducted in the Mekong region, there are no known published reviews of the studies specifically in Vietnam. Here, we review the cause of CNS infections in Vietnam while also considering the potential aetiologies where a cause was not identified, based on the literature from the region. In particular, we focus on the most common pathogens in adults and children including Streptococcus suis which is associated with the consumption of raw pig products, and Japanese encephalitis virus, a mosquito-borne pathogen. We also discuss pathogens less commonly known to cause CNS infections in Vietnam but have been detected in neighbouring countries such as Orientia tsutsugamushi, Rickettsia typhi and Leptospira species and how these may contribute to the unknown causes in Vietnam. We anticipate that this review may help guide future public health measures to reduce the burden of known pathogens and broaden testing to help identify additional aetiologies.

Development of a broad-spectrum epitope-based vaccine against Streptococcus pneumoniae

Streptococcus pneumoniae (SPN) is a significant pathogen causing pneumonia and meningitis, particularly in vulnerable populations like children and the elderly. Available pneumonia vaccines have limitations since they only cover particular serotypes and have high production costs. The emergence of antibiotic-resistant SPN strains further underscores the need for a new, cost-effective, broad-spectrum vaccine. Two potential vaccine candidates, CbpA and PspA, were identified, and their B-cell, CTL, and HTL epitopes were predicted and connected with suitable linkers, adjivant and PADRE sequence. The vaccine construct was found to be antigenic, non-toxic, non-allergenic, and soluble. The three-dimensional structure of the vaccine candidate was built and validated. Docking analysis of the vaccine candidate by ClusPro demonstrated robust and stable binding interactions between the MEV and toll-like receptor 4 in both humans and animals. The iMOD server and Amber v.22 tool has verified the stability of the docking complexes. GenScript server confirmed the high efficiency of cloning for the construct and in-silico cloning into the pET28a (+) vector using SnapGene, demonstrating successful translation of the epitope region. Immunological responses were shown to be enhanced by the C-IMMSIM server. This study introduced a strong peptide vaccine candidate that has the potential to contribute to the development of a rapid and cost-effective solution for combating SPN. However, experimental verification is necessary to evaluate the vaccine's effectiveness.

SPD_0410 negatively regulates capsule polysaccharide synthesis and virulence in Streptococcus pneumoniae D39

Streptococcus pneumoniae capsular polysaccharide (CPS) is a crucial virulence factor for this pathogenic bacterium and is partially under transcriptional control. In this study, we used electrophoretic mobility shift assays and DNA enzyme footprinting to identified the hypothetical protein SPD_0410 as a negative regulator of cps locus. Our results showed that the D39Δspd0410 mutant strain exhibited significantly elevated CPS levels compared to the parental strain D39s. SPD_0410 directly binds at two specific sites on the cps promoter. The regulatory effect of SPD_0410 on CPS was weakened after the mutation of specific binding sites in the promoter. RNAseq analysis revealed that the deletion of spd0410 led to alterations in glucose metabolism. However, the altered glucose levels appeared to eliminate the regulation of CPS synthesis by SPD_0410. Deleting the spd0410 gene resulted in higher invasion and phagocytic resistance of bacteria and in vivo mouse experiments confirmed that D39Δspd0410 caused more severe systemic disease than the parental strain D39s. Our results indicated that SPD_0410 negatively regulates the synthesis of S. pneumoniae capsules and can directly alter pneumococcal virulence.

Sex-based difference in immune responses and efficacy of the pneumococcal conjugate vaccine

Vaccine-mediated protection and susceptibility to Streptococcus pneumoniae (pneumococcus) infections are influenced by biological sex. The incidence of invasive pneumococcal disease remains higher in males compared to females even after the introduction of the pneumococcal conjugate vaccine. However, sex-based differences in the immune response to this conjugate vaccine remain unexplored. To investigate those differences, we vaccinated adult male and female mice with pneumococcal conjugate vaccine and assessed cellular and humoral immune responses. Compared to females, male mice displayed lower levels of T follicular helper cells, germinal center B cells, and plasmablasts, which are all required for antibody production following vaccination. This was linked to lower IgG and IgM levels against pneumococci and lower isotype switching to IgG3 in vaccinated males. Due to lower antibody levels, sera of vaccinated male mice had lower efficacy in several anti-pneumococcal functions, including neutralization of bacterial binding to pulmonary epithelial cells as well as direct cytotoxicity against S. pneumoniae. Importantly, while the vaccine was highly protective in females, vaccinated males succumbed to infection more readily and were more susceptible to both lung-localized infection and systemic spread following S. pneumoniae challenge. These findings identify sex-based differences in immune responses to pneumococcal conjugate vaccine that can inform future vaccine strategies.

Serotype 3 Streptococcus pneumoniae Escapes the Immune Responses Induced by PCV13 in Mice With High Susceptibility to Infection

BACKGROUND

Streptococcus pneumoniae (pneumococcus) is a common cause of respiratory and invasive infections in humans. PCV13, a pneumococcal conjugate vaccine used globally, is highly effective against diseases caused by pneumococcal serotypes included in its formulation. However, one of them, the serotype 3 (ST3) is still being relatively commonly isolated from patients, suggesting an escape from vaccine-induced immunity. The thick capsule produced by ST3 facilitates bacterial evasion from the immune system. Additionally, host immune responses may influence the outcome of ST3 infection. Here we evaluated the influence of inflammation in the adaptive immune responses and protection induced by PCV13 against ST3, using two outbred mice lines that were phenotypically selected for high (AIRmax) and low (AIRmin) inflammatory responses.

METHODS

AIRmin and AIRmax mice were immunized with PCV13. Inbred BALB/c mice were used as reference for vaccine efficacy. Induction of IgG against polysaccharides (PS) from pneumococcal serotype 1 (ST1) and ST3 were evaluated by ELISA. Protection was tested against invasive infections with ST1 and ST3 pneumococcal strains. Sera were compared by IgG binding to pneumococcal surface, induction of pneumococcal agglutination and opsonophagocytosis. The phagocytic capacity of mice-derived neutrophils was also evaluated.

RESULTS

Immunization of AIRmin, AIRmax and BALB/c mice with PCV13 induced IgG against PS from ST1 and ST3 pneumococci. Despite vaccination, AIRmin mice were not protected against fatal infection with ST3. Sera from AIRmin mice immunized with PCV13 presented lower levels of anti-PS3 IgG, with reduced capacity to bind to pneumococcal surface. Reduced capacity to induce opsonophagocytosis of ST3 pneumococci in vitro was also observed. Conversely, PCV13 protected AIRmin mice against fatal infection with ST1 and this correlated with the capacity of the sera to induce ST1 opsonophagocytosis.

CONCLUSIONS

Our results show that both host and bacterial features can influence the outcome of protection induced by PCV13 against ST3 pneumococcal infection.

Nasopharyngeal carriage and antibiotic susceptibility of Streptococcus pneumoniae among diabetes patients in western Kenya

AIMS

To compare nasopharyngeal carriage and antibiotic susceptibility of Streptococcus pneumoniae among patients with and without diabetes at Moi Teaching and Referral Hospital (MTRH) in western Kenya.

METHODS

A cross-sectional study was conducted at MTRH diabetes and eye clinics. Participants were selected using systematic random sampling. Sociodemographic data and risk factors were collected through interviewer-administered questionnaires. Blood samples were taken to measure random blood sugar and HbA1c levels. Nasopharyngeal swabs were cultured and tested for antibiotic susceptibility within 24 h. Data analysis was performed using STATA version 13. Associations were assessed using Pearson's chi-square, Fisher's exact test, unpaired t-test, and Wilcoxon test.

RESULTS

A total of 124 participants with diabetes and 121 without diabetes were enrolled. Overall, 7.4 % (95 % CI: 4.4, 11.4) of participants carried S. pneumoniae. Carriage was higher in diabetes (12.1 % [95 % CI: 7.0, 19.0]) than non-diabetes participants (2.48 % [95 % CI: 1.0, 7.0]), with a statistically significant difference (p = 0.004). Diabetes was associated with higher odds of carriage (adjusted OR 6.2, p = 0.012). No association was found with age, sex, cooking fuel, presence of children under 5, or prior antibiotic use. Among participants with diabetes, carriage of Streptococcus Pneumoniae was only associated with insulin use. Antibiotic resistance was highest for cotrimoxazole (94.44 %), followed by amoxicillin (16.7 %) and cefuroxime (11.1 %). No resistance to macrolides was observed.

CONCLUSION

Nasopharyngeal carriage of S. pneumoniae is higher in patients with diabetes, with significant resistance to common antibiotics, though macrolides remain effective.

Molecular epidemiology of Streptococcus pneumoniae isolates causing invasive and noninvasive infection in Ethiopia

Streptococcus pneumoniae, a medically important opportunistic bacterial pathogen of the upper respiratory tract, is a major public health concern, causing a wide range of pneumococcal illnesses, both invasive and noninvasive. It is associated with significant global morbidity and mortality, including pneumonia, meningitis, sepsis, and acute otitis media. The major purpose of this study was to determine the molecular epidemiology of Streptococcus pneumoniae strains that cause invasive and noninvasive infections in Ethiopia. A prospective study was undertaken in two regional hospitals between January 2018 and December 2019. Whole-genome sequencing was used to analyze all isolates. Serotypes and multilocus sequence types (MLST) were derived from genomic data. The E-test was used for antimicrobial susceptibility testing. Patient samples obtained 54 Streptococcus pneumoniae isolates, 33 from invasive and 21 from noninvasive specimens. Our findings identified 32 serotypes expressed by 25 Global Pneumococcal Sequence Clusters (GPSCs) and 42 sequence types (STs), including 21 new STs. The most common sequence types among the invasive isolates were ST3500, ST5368, ST11162, ST15425, ST15555, ST15559, and ST15561 (2/33, 6% each). These sequence types were linked to serotypes 8, 7 C, 15B/C, 16 F, 10 A, 15B, and 6 A, respectively. Among the noninvasive isolates, only ST15432, associated with serotype 23 A, had numerous isolates (4/21, 19%). Serotype 14 was revealed as the most resistant strain to penicillin G, whereas isolates from serotypes 3, 8, 7 C, and 10 A were resistant to erythromycin. Notably, all serotype 6 A isolates were resistant to both erythromycin and penicillin G. Our findings revealed an abnormally significant number of novel STs, as well as extremely diversified serotypes and sequence types, implying that Ethiopia may serve as a breeding ground for novel STs. Recombination can produce novel STs that cause capsular switching. This has the potential to influence how immunization campaigns affect the burden of invasive pneumococcal illness. The findings highlight the importance of continuous genetic surveillance of the pneumococcal population as a vital step toward enhancing future vaccine design.

Population genomics of Streptococcus mitis in UK and Ireland bloodstream infection and infective endocarditis cases

Streptococcus mitis is a leading cause of infective endocarditis (IE). However, our understanding of the genomic epidemiology and pathogenicity of IE-associated S. mitis is hampered by low IE incidence. Here we use whole genome sequencing of 129 S. mitis bloodstream infection (BSI) isolates collected between 2001-2016 from clinically diagnosed IE cases in the UK to investigate genetic diversity, antimicrobial resistance, and pathogenicity. We show high genetic diversity of IE-associated S. mitis with virtually all isolates belonging to distinct lineages indicating no predominance of specific lineages. Additionally, we find a highly variable distribution of known pneumococcal virulence genes among the isolates, some of which are overrepresented in disease when compared to carriage strains. Our findings suggest that S. mitis in patients with clinically diagnosed IE is not primarily caused by specific hypervirulent or antimicrobial resistant lineages, highlighting the accidental pathogenic nature of S. mitis in patients with clinically diagnosed IE.

Streptococcus pneumoniae Spinal Epidural Abscess in an Immunocompetent Patient

Epidural abscesses are a rare diagnosis in immunocompetent patients. The most common risk factors linked with spinal epidural abscesses are intravenous drug use, diabetes mellitus, hepatitis, and iatrogenic factors like prior surgery and catheter usage. The thoracic and lumbar spine are the most common sites of these abscesses. Clinical presentation can include back pain, fever, and neurologic deterioration, with back pain occurring in almost two-thirds of patients. Staphylococcus aureus is the most common causative pathogen. We present a 50 male with no significant past medical or family history who presented with progressive back pain for greater than one week, chills and malaise. Cervical and lumbar spinal CT scans identified epidural abscesses at C6/7 and L5/S1. Blood cultures and surgical cultures from washout of the epidural space grew Streptococcus pneumoniae. The patient was treated successfully with a prolonged course of cefazolin for six weeks. S. pneumoniae is a rare cause of epidural abscesses, especially in patients with no known risk factors for invasive disease. This case demonstrates that invasive pneumococcal disease should remain on the differential diagnosis even in immunocompetent patients.

Respiratory tract infections: an update on the complexity of bacterial diversity, therapeutic interventions and breakthroughs

Respiratory tract infections (RTIs) have a significant impact on global health, especially among children and the elderly. The key bacterial pathogens Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, Staphylococcus aureus and non-fermenting Gram Negative bacteria such as Acinetobacter baumannii and Pseudomonas aeruginosa are most commonly associated with RTIs. These bacterial pathogens have evolved a diverse array of resistance mechanisms through horizontal gene transfer, often mediated by mobile genetic elements and environmental acquisition. Treatment failures are primarily due to antimicrobial resistance and inadequate bacterial engagement, which necessitates the development of alternative treatment strategies. To overcome this, our review mainly focuses on different virulence mechanisms and their resulting pathogenicity, highlighting different therapeutic interventions to combat resistance. To prevent the antimicrobial resistance crisis, we also focused on leveraging the application of artificial intelligence and machine learning to manage RTIs. Integrative approaches combining mechanistic insights are crucial for addressing the global challenge of antimicrobial resistance in respiratory infections.

Novel manufacturing process of pneumococcal capsular polysaccharides using advanced sterilization methods

Pneumococcal disease is caused by Streptococcus pneumoniae, including pneumonia, meningitis and sepsis. Capsular polysaccharides (CPSs) have been shown as effective antigens to stimulate protective immunity against pneumococcal disease. A major step in the production of pneumococcal vaccines is to prepare CPSs that meet strict quality standards in immunogenicity and safety. The major impurities come from bacterial proteins, nucleic acids and cell wall polysaccharides. Traditionally, the impurity level of refined CPSs is reduced by optimization of purification process. In this study, we investigated new aeration strategy and advanced sterilization methods by formaldehyde or β-propiolactone (BPL) to increase the amount of soluble polysaccharide in fermentation supernatant and to prevent bacterial lysis during inactivation. Furthermore, we developed a simplified process for the CPS purification, which involves ultrafiltration and diafiltration, followed by acid and alcohol precipitation, and finally diafiltration and lyophilization to obtain pure polysaccharide. The CPSs prepared from formaldehyde and BPL sterilization contained significantly lower level of residual impurities compared to the refined CPSs obtained from traditional deoxycholate sterilization. Finally, we showed that this novel approach of CPS preparation can be scaled up for polysaccharide vaccine production.

Development and evaluation of a real-time multienzyme isothermal rapid amplification assay for rapid detection of Streptococcus pneumoniae

Streptococcus pneumoniae is a significant pathogen causing infectious diseases, including pneumonia, otitis media, septicemia, and meningitis. The introduction of multivalent vaccines has coincided with a remarkable decrease in the number of pneumococcal-related deaths. Despite this, pneumococcal infection remains a significant cause of death among children under 5 years old and adults aged 65 or older at a global level. Therefore, early detection of S. pneumoniae infection is crucial for prognosis of pneumococcal infection patients. In this study, we evaluated the utility of a real-time multienzyme isothermal rapid amplification (MIRA) assay for detecting S. pneumoniae and other non-S. pneumoniae bacterial species. A primer-probe set targeting the S. pneumoniae lytA gene was designed, followed by optimization of parameters for the MIRA assay. At the same time, we validated the real-time MIRA assay for detecting S. pneumoniae using 79 clinical isolates identified by VITEK MS. The results showed a detection sensitivity and specificity of 100%. These results demonstrate that the designed real-time MIRA assay is a promising, rapid, simple, and reliable method for detecting S. pneumoniae infection in resource-limited areas. It has great potential for application in detecting not only S. pneumoniae but also other non-S. pneumoniae bacterial species.

Serotype distribution, antibiotic resistance, multilocus sequence typing, and virulence factors of invasive and non-invasive Streptococcus pneumoniae in Northeast China from 2000 to 2021

Streptococcus pneumoniae infection is a major public health concern with high morbidity and mortality rates. This study aimed to evaluate the serotype distribution, antimicrobial resistance changes, clonal composition, and virulence factors of S. pneumoniae isolates causing pneumococcal disease in northeast China from 2000 to 2021. A total of 1,454 S. pneumoniae isolates were included, with 568 invasive strains and 886 non-invasive strains. The patients from whom the S. pneumoniae were isolated ranged in age from 26 days to 95 years, with those ≤ 5 years old comprising the largest group (67.19%). 19 F, 19 A, 23 F, 14, and 6B were the most common serotypes, of which 19 A and 19 F were the main serotypes of invasive and non-invasive S. pneumoniae, respectively. CC271 was the most common multilocus sequence type. Serotype 14 had the lowest expression of cbpA, rrgA, and psrP genes, but expression levels of 19 A and 19 F genes were similar. All isolates were sensitive to ertapenem, moxifloxacin, linezolid, and vancomycin but highly resistant to macrolides, tetracyclines, and cotrimoxazole. Simultaneous resistance to erythromycin, clindamycin, tetracyclines, and trimethoprim/sulfamethoxazole was common pattern among multidrug-resistant isolates. Non-invasive S. pneumoniae had higher resistance to β-lactam antibiotics than invasive strains. 19 A and 19 F were the main strains of penicillin-resistant S. pneumoniae. The resistance rate of β-lactam antibiotics decreased from 2017 to 2021 compared to previous periods. Including PCV13 in the national immunization program can reduce the morbidity and mortality rates of pneumococcal disease effectively.

Streptococcus pneumoniae extracellular vesicles aggravate alveolar epithelial barrier disruption via autophagic degradation of OCLN (occludin)

Streptococcus pneumoniae (S. pneumoniae) represents a major human bacterial pathogen leading to high morbidity and mortality in children and the elderly. Recent research emphasizes the role of extracellular vesicles (EVs) in bacterial pathogenicity. However, the contribution of S. pneumoniae EVs (pEVs) to host-microbe interactions has remained unclear. Here, we observed that S. pneumoniae infections in mice led to severe lung injuries and alveolar epithelial barrier (AEB) dysfunction. Infections of S. pneumoniae reduced the protein expression of tight junction protein OCLN (occludin) and activated macroautophagy/autophagy in lung tissues of mice and A549 cells. Mechanically, S. pneumoniae induced autophagosomal degradation of OCLN leading to AEB impairment in the A549 monolayer. S. pneumoniae released the pEVs that could be internalized by alveolar epithelial cells. Through proteomics, we profiled the cargo proteins inside pEVs and found that these pEVs contained many virulence factors, among which we identified a eukaryotic-like serine-threonine kinase protein StkP. The internalized StkP could induce the phosphorylation of BECN1 (beclin 1) at Ser93 and Ser96 sites, initiating autophagy and resulting in autophagy-dependent OCLN degradation and AEB dysfunction. Finally, the deletion of stkP in S. pneumoniae completely protected infected mice from death, significantly alleviated OCLN degradation in vivo, and largely abolished the AEB disruption caused by pEVs in vitro. Overall, our results suggested that pEVs played a crucial role in the spread of S. pneumoniae virulence factors. The cargo protein StkP in pEVs could communicate with host target proteins and even hijack the BECN1 autophagy initiation pathway, contributing to AEB disruption and bacterial pathogenicity.Abbreviations: AEB: alveolarepithelial barrier; AECs: alveolar epithelial cells; ATG16L1: autophagy related 16 like 1; ATP:adenosine 5'-triphosphate; BafA1: bafilomycin A1; BBB: blood-brain barrier; CFU: colony-forming unit; co-IP: co-immunoprecipitation; CQ:chloroquine; CTRL: control; DiO: 3,3'-dioctadecylox-acarbocyanineperchlorate; DOX: doxycycline; DTT: dithiothreitol; ECIS: electricalcell-substrate impedance sensing; eGFP: enhanced green fluorescentprotein; ermR: erythromycin-resistance expression cassette; Ery: erythromycin; eSTKs: eukaryotic-like serine-threoninekinases; EVs: extracellular vesicles; HA: hemagglutinin; H&E: hematoxylin and eosin; HsLC3B: human LC3B; hpi: hours post-infection; IP: immunoprecipitation; KD: knockdown; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LC/MS: liquid chromatography-mass spectrometry; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MVs: membranevesicles; NC:negative control; NETs:neutrophil extracellular traps; OD: optical density; OMVs: outer membrane vesicles; PBS: phosphate-buffered saline; pEVs: S.pneumoniaeextracellular vesicles; protK: proteinase K; Rapa: rapamycin; RNAi: RNA interference; S.aureus: Staphylococcusaureus; SNF:supernatant fluid; sgRNA: single guide RNA; S.pneumoniae: Streptococcuspneumoniae; S.suis: Streptococcussuis; TEER: trans-epithelium electrical resistance; moi: multiplicity ofinfection; TEM:transmission electron microscope; TJproteins: tight junction proteins; TJP1/ZO-1: tight junction protein1; TSA: tryptic soy agar; WB: western blot; WT: wild-type.

Qualification of a 21-valent pneumococcal urine antigen detection assay and development of clinical positivity cutoffs

Aim: Serotype-specific assays detecting pneumococcal polysaccharides in bodily fluids are needed to understand the pneumococcal serotype distribution in non-bacteremic pneumonia.Methods: We developed a urine antigen detection assay and using urine samples from adult outpatients without pneumonia developed positivity cutoffs for both a previously published 15-valent and the new 21-valent assay. Clinical sensitivity was confirmed with samples from patients with invasive pneumococcal disease.Results: Total assay precision ranged from 7.6 to 17.8% coefficient of variation while accuracy ranged between 80 and 150% recovery, except for three serotypes where recoveries ranged from 32 to 60%. Clinical sensitivity was 86.4% and specificity was 96.5% across all 30 serotypes.Conclusion: The assay could potentially assess serotype-distribution in non-infected and infected participants with pneumococcal disease.

Individual Atg8 paralogs and a bacterial metabolite sequentially promote hierarchical CASM-xenophagy induction and transition

Atg8 paralogs, consisting of LC3A/B/C and GBRP/GBRPL1/GATE16, function in canonical autophagy; however, their function is controversial because of functional redundancy. In innate immunity, xenophagy and non-canonical single membranous autophagy called "conjugation of Atg8s to single membranes" (CASM) eliminate bacteria in various cells. Previously, we reported that intracellular Streptococcus pneumoniae can induce unique hierarchical autophagy comprised of CASM induction, shedding, and subsequent xenophagy. However, the molecular mechanisms underlying these processes and the biological significance of transient CASM induction remain unknown. Herein, we profile the relationship between Atg8s, autophagy receptors, poly-ubiquitin, and Atg4 paralogs during pneumococcal infection to understand the driving principles of hierarchical autophagy and find that GATE16 and GBRP sequentially play a pivotal role in CASM shedding and subsequent xenophagy induction, respectively, and LC3A and GBRPL1 are involved in CASM/xenophagy induction. Moreover, we reveal ingenious bacterial tactics to gain intracellular survival niches by manipulating CASM-xenophagy progression by generating intracellular pneumococci-derived H2O2.

Synthetic BSA-conjugated disaccharide related to the Streptococcus pneumoniae serotype 3 capsular polysaccharide increases IL-17A Levels, γδ T cells, and B1 cells in mice

The disaccharide (β-D-glucopyranosyluronic acid)-(1→4)-β-D-glucopyranoside represents a repeating unit of the capsular polysaccharide of Streptococcus pneumoniae serotype 3. A conjugate of the disaccharide with BSA (di-BSA conjugate) adjuvanted with aluminum hydroxide induced - in contrast to the non-adjuvanted conjugate - IgG1 antibody production and protected mice against S. pneumoniae serotype 3 infection after intraperitoneal prime-boost immunization. Adjuvanted and non-adjuvanted conjugates induced production of Th1 (IFNγ, TNFα); Th2 (IL-5, IL-13); Th17 (IL-17A), Th1/Th17 (IL-22), and Th2/Th17 cytokines (IL-21) after immunization. The concentration of cytokines in mice sera was higher in response to the adjuvanted conjugate, with the highest level of IL-17A production after the prime and boost immunizations. In contrast, the non-adjuvanted conjugate elicited only weak production of IL-17A, which gradually decreased after the second immunization. After boost immunization of mice with the adjuvanted di-BSA conjugate, there was a significant increase in the number of CD45+/CD19+ B cells, TCR+ γδ T cell, CD5+ В1 cells, and activated cells with MHC II+ expression in the spleens of the mice. IL-17A, TCR+ γδ T cells, and CD5+ В1 cells play a crucial role in preventing pneumococcal infection, but can also contribute to autoimmune diseases. Immunization with the adjuvanted and non-adjuvanted di-BSA conjugate did not elicit autoantibodies against double-stranded DNA targeting cell nuclei in mice. Thus, the molecular and cellular markers associated with antibody production and protective activity in response to immunization with the di-BSA conjugate adjuvanted with aluminum hydroxide are IL-17A, TCR+ γδ T cells, and CD5+ В1 cells against the background of increasing MHC II+ expression.

The prostaglandin D2 antagonist asapiprant ameliorates clinical severity in young hosts infected with invasive Streptococcus pneumoniae

Streptococcus pneumoniae (pneumococcus) remains a serious cause of pulmonary and systemic infections globally, and host-directed therapies are lacking. The aim of this study was to test the therapeutic efficacy of asapiprant, an inhibitor of prostaglandin D2 signaling, against pneumococcal infection. Treatment of young mice with asapiprant after pulmonary infection with invasive pneumococci significantly reduced systemic spread, disease severity, and host death. Protection was specific against bacterial dissemination from the lung to the blood but had no effect on pulmonary bacterial burden. Asapiprant-treated mice had enhanced antimicrobial activity in circulating neutrophils, elevated levels of reactive oxygen species (ROS) in lung macrophages/monocytes, and improved pulmonary barrier integrity indicated by significantly reduced diffusion of fluorescein isothiocyanate (FITC)-dextran from lungs into the circulation. These findings suggest that asapiprant protects the host against pneumococcal dissemination by enhancing the antimicrobial activity of immune cells and maintaining epithelial/endothelial barrier integrity in the lungs.

Spontaneous mutations and mutational responses to penicillin treatment in the bacterial pathogen Streptococcus pneumoniae D39

Bacteria with functional DNA repair systems are expected to have low mutation rates due to strong natural selection for genomic stability. However, our study of the wild-type Streptococcus pneumoniae D39, a pathogen responsible for many common diseases, revealed a high spontaneous mutation rate of 0.02 per genome per cell division in mutation-accumulation (MA) lines. This rate is orders of magnitude higher than that of other non-mutator bacteria and is characterized by a high mutation bias in the A/T direction. The high mutation rate may have resulted from a reduction in the overall efficiency of selection, conferred by the tiny effective population size in nature. In line with this, S. pneumoniae D39 also exhibited the lowest DNA mismatch-repair (MMR) efficiency among bacteria. Treatment with the antibiotic penicillin did not elevate the mutation rate, as penicillin did not induce DNA damage and S. pneumoniae lacks a stress response pathway. Our findings suggested that the MA results are applicable to within-host scenarios and provide insights into pathogen evolution.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00220-6.

Neighborhood-level disadvantages increase risk for invasive pneumococcal disease

BACKGROUND

Streptococcus pneumoniae (Spn) infection remains common worldwide despite recent vaccine efforts. Invasive pneumococcal disease (IPD) is the most severe form of Spn infection. Known individual risk factors for IPD include male gender and African American race. However, area-level socioeconomic factors have not been assessed. We examined the association of neighborhood-level disadvantages and risk of IPD in a tertiary medical center located in a socioeconomic diverse urban area in the Southeastern United States.

METHODS

Patients hospitalized with culture-confirmed Streptococcus pneumoniae (Spn) infection from 01/01/2010 - 12/31/2019 were identified from electronic health record (EHR). The cohort's demographic and clinical information were obtained from EHR. Patients' residential address was geocoded and matched to 2015 area deprivation index (ADI). The association of ADI and IPD was evaluated using logistic regression after controlling for the demographic information (age, sex, race) and clinical factors (BMI, smoking status, alcoholism, immunosuppressive status, vaccination status, comorbidities).

RESULTS

A total of 268 patients were hospitalized with culture-positive Streptococcus pneumoniae infection and 92 (34.3%) of them had IPD. The analysis showed that higher neighborhood deprivation (ADI in 79-100) was associated with increased risk of developing IPD in younger patients with age less than 65 (p = 0.007) after controlling for the individual demographic information and clinical factors.

CONCLUSIONS

ADI is a risk factor for IPD in younger adults. Community-level socioeconomic risk factors should be considered when developing prevention strategies such as increasing vaccine uptake in high risk population to reduce the disease burden of IPD.

Streptococcus pneumoniae as a colonizing agent of the Nasopharynx - Oropharynx in adults: A systematic review and meta-analysis

BACKGROUND

Streptococcus pneumoniae (Spn) is a commensal pathogen that usually colonizes the upper respiratory tract of children. Likewise, Spn colonization has been considered a critical factor in the development of pneumococcal invasive disease. However, Spn prevalence in adults remains unclear. This study performs a systematic review and meta-analysis to explore the prevalence of Spn Nasopharynx - Oropharynx Colonization (NOC) in adults.

METHODS

A Systematic review of scientific databases was utilized to identify eligible studies that follow strict selection criteria. Subsequently, a meta-analysis was conducted to establish NOC prevalence in adults (≥18 years old). The heterogeneity and sensitivity analyses were assessed using the microorganism identification technique, sample type, and age subgroups.

RESULTS

Initial selection includes 69 studies, with 37 selected for the meta-analysis, involving 23,724 individuals. The overall prevalence (95 % CI) of Spn NOC among adults was 6 % (5-9). The subgroup analysis revealed that young adults (YA), 18-64 years old, had a prevalence of 10 %, whereas older adults (OA), ≥65 years old, had a prevalence of 2 %. The identification of Spn NOC may vary depending on the method of diagnosis used. High heterogeneity (I2 > 90 %) was observed but diminished to 70 % when the analysis was restricted to oropharyngeal swabs as an identification method. Furthermore, heterogeneity decreased to 58 % when exclusively employing traditional culture as the identification method.

CONCLUSIONS

This study found a low prevalence of Spn NOC in adults. Notably, the prevalence of Spn NOC was higher in younger adults than in older adults. It is essential to highlight a significant heterogeneity among studies, which indicates there is no standardized method of Spn NOC identification.

Genetic- and fiber-diet-mediated changes in virulence factors in pig colon contents and feces and their driving factors

Virulence factors (VFs) are key factors for microorganisms to establish defense mechanisms in the host and enhance their pathogenic potential. However, the spectrum of virulence factors in pig colon and feces, as well as the influence of dietary and genetic factors on them, remains unreported. In this study, we firstly revealed the diversity, abundance and distribution characteristics of VFs in the colonic contents of different breeds of pigs (Taoyuan, Xiangcun and Duroc pig) fed with different fiber levels by using a metagenomic analysis. The analysis resulted in the identification of 1,236 virulence factors, which could be grouped into 16 virulence features. Among these, Taoyuan pigs exhibited significantly higher levels of virulence factors compared to Duroc pigs. The high-fiber diet significantly reduced the abundance of certain virulence factor categories, including iron uptake systems (FbpABC, HitABC) and Ig protease categories in the colon, along with a noteworthy decrease in the relative abundance of plasmid categories in mobile genetic elements (MGEs). Further we examined VFs in feces using absolute quantification. The results showed that high-fiber diets reduce fecal excretion of VFs and that this effect is strongly influenced by MGEs and short-chain fatty acids (SCFAs). In vitro fermentation experiments confirmed that acetic acid (AA) led to a decrease in the relative abundance of VFs (p < 0.1). In conclusion, our findings reveal for the first time how fiber diet and genetic factors affect the distribution of VFs in pig colon contents and feces and their driving factors. This information provides valuable reference data to further improve food safety and animal health.

Identification and genetic engineering of pneumococcal capsule-like polysaccharides in commensal oral streptococci

Capsular polysaccharides (CPS) in Streptococcus pneumoniae are pivotal for bacterial virulence and present extensive diversity. While oral streptococci show pronounced antigenicity toward pneumococcal capsule-specific sera, insights into evolution of capsule diversity remain limited. This study reports a pneumococcal CPS-like genetic locus in Streptococcus parasanguinis, a predominant oral Streptococcus. The discovered locus comprises 15 genes, mirroring high similarity to those from the Wzy-dependent CPS locus of S. pneumoniae. Notably, S. parasanguinis elicited a reaction with pneumococcal 19B antiserum. Through nuclear magnetic resonance analysis, we ascertained that its CPS structure matches the chemical composition of the pneumococcal 19B capsule. By introducing the glucosyltransferase gene cps19cS from a pneumococcal serotype 19C, we successfully transformed S. parasanguinis antigenicity from 19B to 19C. Furthermore, substituting serotype-specific genes, cpsI and cpsJ, with their counterparts from pneumococcal serotype 19A and 19F enabled S. parasanguinis to generate 19A- and 19F-specific CPS, respectively. These findings underscore that S. parasanguinis harbors a versatile 19B-like CPS adaptable to other serotypes. Remarkably, after deleting the locus's initial gene, cpsE, responsible for sugar transfer, we noted halted CPS production, elongated bacterial chains, and diminished biofilm formation. A similar phenotype emerged with the removal of the distinct gene cpsZ, which encodes a putative autolysin. These data highlight the importance of S. parasanguinis CPS for biofilm formation and propose a potential shared ancestry of its CPS locus with S. pneumoniae.

IMPORTANCE

Diverse capsules from Streptococcus pneumoniae are vital for bacterial virulence and pathogenesis. Oral streptococci show strong responses to a wide range of pneumococcal capsule-specific sera. Yet, the evolution of this capsule diversity in relation to microbe-host interactions remains underexplored. Our research delves into the connection between commensal oral streptococcal and pneumococcal capsules, highlighting the potential for gene transfer and evolution of various capsule types. Understanding the genetic and evolutionary factors that drive capsule diversity in S. pneumoniae and its related oral species is essential for the development of effective pneumococcal vaccines. The present findings provide fresh perspectives on the cross-reactivity between commensal streptococci and S. pneumoniae, its influence on bacteria-host interactions, and the development of new strategies to manage and prevent pneumococcal illnesses by targeting and modulating commensal streptococci.

Necrotizing Pneumonia With Extensive Lobar Cavitation

Pneumonia occupies one of the leading positions in morbidity and mortality worldwide. It is frequently categorized depending on the site of acquisition. Here, we present a case of a young woman who was admitted to the Emergency Department (ED) with cough, dyspnea, fever, and progressive worsening associated with palpitations and hypotension. An initial x-ray was followed by a computed tomography (CT) scan of the chest, which revealed signs of extensive left lung pneumonia with pleural effusion. Despite initial improvement after antibiotic treatment, the patient's condition declined. A repeat chest CT showed evidence of extensive lobar cavitations, leading to suspicion of tuberculosis.

RNA cis-regulators are important for Streptococcus pneumoniae in vivo success

Bacteria have evolved complex transcriptional regulatory networks, as well as many diverse regulatory strategies at the RNA level, to enable more efficient use of metabolic resources and a rapid response to changing conditions. However, most RNA-based regulatory mechanisms are not well conserved across different bacterial species despite controlling genes important for virulence or essential biosynthetic processes. Here, we characterize the activity of, and assess the fitness benefit conferred by, twelve cis-acting regulatory RNAs (including several riboswitches and a T-box), in the opportunistic pathogen Streptococcus pneumoniae TIGR4. By evaluating native locus mutants of each regulator that result in constitutively active or repressed expression, we establish that growth defects in planktonic culture are associated with constitutive repression of gene expression, while constitutive activation of gene expression is rarely deleterious. In contrast, in mouse nasal carriage and pneumonia models, strains with either constitutively active and repressed gene expression are significantly less fit than matched control strains. Furthermore, two RNA-regulated pathways, FMN synthesis/transport and pyrimidine synthesis/transport display exceptional sensitivity to mis-regulation or constitutive gene repression in both planktonic culture and in vivo environments. Thus, despite lack of obvious phenotypes associated with constitutive gene expression in vitro, the fitness benefit conferred on bacteria via fine-tuned metabolic regulation through cis-acting regulatory RNAs is substantial in vivo, and therefore easily sufficient to drive the evolution and maintenance of diverse RNA regulatory mechanisms.

Cold-inducible RNA-binding protein induces inflammatory responses via NF-κB signaling pathway in normal human bronchial epithelial cells infected with streptococcus pneumoniae

BACKGROUND

Community-acquired pneumonia causes significant illness and death worldwide, requiring further investigation and intervention. The invasion of Streptococcus pneumoniae (S. pneumoniae, S.p) can lead to serious conditions like meningitis, sepsis, or pneumonia. Extracellular Cold-inducible RNA-binding protein (eCIRP) acts as a damage-associated molecular pattern that triggers inflammatory responses and plays an important role in both acute and chronic inflammatory diseases. It remains unclear whether CIRP is involved in the process of S. pneumoniae infection in normal human bronchial epithelial cells (BEAS-2B).

METHODS

Cell counting kit (CCK)-8 assay was used to detect the activity of BEAS-2B cells. The subcellular localization of CIRP was detected by immunofluorescence. The mRNA and protein levels of CIRP, nuclear factor kappa-B (NF-κB) p65, toll like receptor-4 (TLR4), interleukin-6 (IL-6) were detected using quantitative real-time PCR (PCR) and Western Blot (WB). The protein expressions of CIRP, IL-1β, IL-6, tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) were assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

CIRP affects the activity of BEAS-2B cells induced by S. pneumoniae infection. After infection, CIRP translocates from the nucleus to the cytoplasm, thereby inducing the production of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, and MCP-1). Additionally, the NF-κB p65 protein increases in infected cells but decreases with si-CIRP interference. Treatment with TLR4 neutralizing antibodies or NF-κB inhibitor effectively reduces the expressions of IL-1β, IL-6, TNF-α, and MCP-1.

CONCLUSIONS

The infection with S. pneumoniae upregulates CIRP expression and translocates it from the nucleus to the cytoplasm in BEAS-2B cells, leading to the release of proinflammatory factors via activation of NF-κB signaling pathway. CIRP as a key mediator in S. pneumoniae-induced inflammation offers potential targets for therapeutic intervention against community-acquired pneumonia.

Oxidation of hemoproteins by Streptococcus pneumoniae collapses the cell cytoskeleton and disrupts mitochondrial respiration leading to the cytotoxicity of human lung cells

IMPORTANCE

Streptococcus pneumoniae (Spn) colonizes the lungs, killing millions every year. During its metabolism, Spn produces abundant amounts of hydrogen peroxide. When produced in the lung parenchyma, Spn-hydrogen peroxide (H2O2) causes the death of lung cells, and details of the mechanism are studied here. We found that Spn-H2O2 targets intracellular proteins, resulting in the contraction of the cell cytoskeleton and disruption of mitochondrial function, ultimately contributing to cell death. Intracellular proteins targeted by Spn-H2O2 included cytochrome c and, surprisingly, a protein of the cell cytoskeleton, beta-tubulin. To study the details of oxidative reactions, we used, as a surrogate model, the oxidation of another hemoprotein, hemoglobin. Using the surrogate model, we specifically identified a highly reactive radical whose creation was catalyzed by Spn-H2O2. In sum, we demonstrated that the oxidation of intracellular targets by Spn-H2O2 plays an important role in the cytotoxicity caused by Spn, thus providing new targets for interventions.

Antimicrobial Resistance in Streptococcus pneumoniae before and after the Introduction of Pneumococcal Conjugate Vaccines in Brazil: A Systematic Review

Streptococcus pneumoniae causes serious illnesses, such as pneumonia, bacteremia, and meningitis, mainly in immunocompromised individuals and those of extreme ages. Currently, pneumococcal conjugate vaccines (PCVs) are the best allies against pneumococcal diseases. In Brazil, the 10-valent and 13-valent PCVs have been available since 2010, but the threat of antimicrobial resistance persists and has been changing over time. We conducted a systematic review of the literature with works published since 2000, generating a parallel between susceptibility data on isolates recovered from colonization and invasive diseases before and after the implementation of PCVs for routine childhood use in Brazil. This systematic review was based on the Cochrane Handbook for Systematic Reviews of Interventions and Preferred Reporting Items for Systematic Literature Reviews and Meta-Analyses (PRISMA) guidelines. Despite the inclusion of PCVs at a large scale in the national territory, high frequencies of non-susceptibility to important drugs used in pneumococcal diseases are still observed, especially penicillin, as well as increasing resistance to macrolides. However, there are still drugs for which pneumococci have a comprehensive sensitivity profile.

Disease-Associated Streptococcus pneumoniae Genetic Variation

Streptococcus pneumoniae is an opportunistic pathogen that causes substantial illness and death among children worldwide. The genetic backgrounds of pneumococci that cause infection versus asymptomatic carriage vary substantially. To determine the evolutionary mechanisms of opportunistic pathogenicity, we conducted a genomic surveillance study in China. We collected 783 S. pneumoniae isolates from infected and asymptomatic children. By using a 2-stage genomewide association study process, we compared genomic differences between infection and carriage isolates to address genomic variation associated with pathogenicity. We identified 8 consensus k-mers associated with adherence, antimicrobial resistance, and immune modulation, which were unevenly distributed in the infection isolates. Classification accuracy of the best k-mer predictor for S. pneumoniae infection was good, giving a simple target for predicting pathogenic isolates. Our findings suggest that S. pneumoniae pathogenicity is complex and multifactorial, and we provide genetic evidence for precise targeted interventions.

In silico design of an epitope-based vaccine against PspC in Streptococcus pneumoniae using reverse vaccinology

BACKGROUND

Streptococcus pneumoniae is a major pathogen that poses a significant hazard to global health, causing a variety of infections including pneumonia, meningitis, and sepsis. The emergence of antibiotic-resistant strains has increased the difficulty of conventional antibiotic treatment, highlighting the need for alternative therapies such as multi-epitope vaccines. In this study, immunoinformatics algorithms were used to identify potential vaccine candidates based on the extracellular immunogenic protein Pneumococcal surface protein C (PspC).

METHOD

The protein sequence of PspC was retrieved from NCBI for the development of the multi-epitope vaccine (MEV), and potential B cell and T cell epitopes were identified. Linkers including EAAAK, AAY, and CPGPG were used to connect the epitopes. Through molecular docking, molecular dynamics, and immunological simulation, the affinity between MEV and Toll-like receptors was determined. After cloning the MEV construct into the PET28a ( +) vector, SnapGene was used to achieve expression in Escherichia coli.

RESULT

The constructed MEV was discovered to be stable, non-allergenic, and antigenic. Microscopic interactions between ligand and receptor are confirmed by molecular docking and molecular dynamics simulation. The use of an in-silico cloning approach guarantees the optimal expression and translation efficiency of the vaccine within an expression vector.

CONCLUSION

Our study demonstrates the potential of in silico approaches for designing effective multi-epitope vaccines against S. pneumoniae. The designated vaccine exhibits the required physicochemical, structural, and immunological characteristics of a successful vaccine against SPN. However, laboratory validation is required to confirm the safety and immunogenicity of the proposed vaccine design.