Immunization with pneumococcal neuraminidases NanA, NanB and NanC to generate neutralizing antibodies and to increase survival in mice

Streptococcus pneumoniae serotype 19A from carriers and invasive disease: virulence gene profile and pathogenicity in a Galleria mellonella model

PURPOSE

This study aimed to evaluate and compare the presence of genes related to surface proteins between isolates of Streptococcus pneumoniae from healthy carriers (HC) and invasive pneumococcal disease (IPD) with a particular focus on serotype 19A.

METHODS

The presence of these genes was identified by real-time PCR. Subsequently, we employed the Galleria mellonella larval infection model to study their effect on pathogenicity in vivo.

RESULTS

The percentage of selected virulence genes was similar between the HC and IPD groups (p > 0.05), and the genes lytA, nanB, pavA, pcpA, phtA, phtB, phtE, rrgA, and sipA were all present in both groups. However, the virulence profile of the isolates differed individually between HC and IPD groups. The highest lethality in G. mellonella was for IPD isolates (p < 0.01), even when the virulence profile was the same as compared to the HC isolates or when the nanA, pspA, pspA-fam1, and pspC genes were not present.

CONCLUSIONS

The occurrence of the investigated virulence genes was similar between HC and IPD S. pneumoniae serotype 19A groups. However, the IPD isolates showed a higher lethality in the alternative G. mellonella model than the HC isolates, regardless of the virulence gene composition, indicating that other virulence factors may play a decisive role in virulence. Currently, this is the first report using the in vivo G. mellonella model to study the virulence of clinical isolates of S. pneumoniae.

Psp140: an immunodominant antigen in the supernatant of Streptococcus pneumoniae culture

Background and Objectives:

Streptococcus pneumoniae causes many lethal infections. Due to its reduced sensitivity to commonly used antibiotics, development of new strategies against pneumococcal infections seems to be necessary. We aimed to investigate immunodominant antigens in S. pneumoniae culture supernatant in order to develop novel targets for pneumococcal vaccines.

Materials and Methods:

In this study S. pneumoniae ATCC49619 was sub-cultured into BHI broth from overnight culture at 37°C for 4 h. The supernatant proteins were precipitated using acetone precipitation method. A rabbit was intramuscularly immunized with alum adjuvant and 100 μg pneumococcal supernatant proteins, 6 times at 14 days’ intervals to produce hyperimmune serum. ELISA assay was performed to determine the antibody level response to pneumococcal secretory proteins. Then dot blot applied for rapid evaluation of hyperimmune serum reactivity to pneumococcus supernatant proteins. The western blot was also used to determine the interaction of supernatant proteins with immunogenic rabbit’s hyperimmune-serum.

Results:

According to the western blot analysis, the immunodominant protein had 140KDa molecular weight and designated as pneumococcal secretory protein140 (Psp140).

Conclusion:

The Psp140 protein in the supernatant of S. pneumoniae culture is an immunodominant protein and it is likely related to pneumococcal secretory protein or surface exposed protein which released into culture supernatant during bacterial growth.

Role of BgaA as a Pneumococcal Virulence Factor Elucidated by Molecular Evolutionary Analysis

Streptococcus pneumoniae is a major cause of pneumonia, sepsis, and meningitis. Previously, we identified a novel virulence factor by investigating evolutionary selective pressure exerted on pneumococcal choline-binding cell surface proteins. Herein, we focus on another pneumococcal cell surface protein. Cell wall-anchoring proteins containing the LPXTG motif are conserved in Gram-positive bacteria. Our evolutionary analysis showed that among the examined genes, nanA and bgaA had high proportions of codon that were under significant negative selection. Both nanA and bgaA encode a multi-functional glycosidase that aids nutrient acquisition in a glucose-poor environment, pneumococcal adherence to host cells, and evasion from host immunity. However, several studies have shown that the role of BgaA is limited in a mouse pneumonia model, and it remains unclear if BgaA affects pneumococcal pathogenesis in a mouse sepsis model. To evaluate the distribution and pathogenicity of bgaA, we performed phylogenetic analysis and intravenous infection assay. In both Bayesian and maximum likelihood phylogenetic trees, the genetic distances between pneumococcal bgaA was small, and the cluster of pneumococcal bgaA did not contain other bacterial orthologs except for a Streptococcus gwangjuense gene. Evolutionary analysis and BgaA structure indicated BgaA active site was not allowed to change. The mouse infection assay showed that the deletion of bgaA significantly reduced host mortality. These results indicated that both nanA and bgaA encode evolutionally conserved pneumococcal virulence factors and that molecular evolutionary analysis could be a useful alternative strategy for identification of virulence factors.

Thomsen-Friedenreich antigen activation as a predictor for clinical outcome of pediatric patients with invasive pneumococcal disease

BACKGROUND

The most severe form of pneumococcal disease is invasive pneumococcal disease (IPD), including empyema, sepsis and meningitis. Thomsen-Friedenreich antigen (TA; Galβ1-3GalNAc) activation is known to be a predictor of Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS). There have been limited data to correlate TA activation and overall disease severity of IPD in children. The study aimed to prove the positive correlation between TA activation and disease severity and to demonstrate the trend of TA level during the disease course.

METHODS

We retrospectively reviewed the medical records from 38 pediatric patients aged from 0 to 18 years with microbiologically-confirmed IPD between 2010 and 2015 at a medical center in Taiwan. All cases underwent TA activation testing by the fluorescence-labeled peanut lectin agglutination method. Medical information including demographic data, laboratory findings, co-morbidities, and outcome was collected and reviewed. We compared the clinical manifestations and associated co-morbidities between TA-positive and TA-negative patients.

RESULTS

Among the 38 patients, 25 (66%) showed TA activation. Compared to TA-negative patients, patients with TA activation had a statistically higher rate of prolonged anemia, thrombocytopenia, and acute kidney injury. TA-positive patients also had a longer intensive care unit stay and overall hospitalization days. The TA levels usually peaked 5-10 days after disease onset. Twenty-one pneumococcal isolates were recovered from the patients and serotyping was determined in 11 isolates: 10 serotype 19A and 1 serotype 3.

CONCLUSIONS

TA determination not only helps to diagnose Sp-HUS but also is a predictor for IPD severity. Among hospitalized patients with severe pneumococcal disease, the peak of TA level usually appeared 5-10 days after disease onset.

Prevalence of Various Vaccine Candidate Proteins in Clinical Isolates of Streptococcus pneumoniae: Characterization of the Novel Pht Fusion Proteins PhtA/B and PhtA/D

Pneumococcal proteins unrelated to serotypes are considered to be candidates of antigens in next-generation vaccines. In the present study, the prevalence of vaccine candidate protein genes, along with serotypes and antimicrobial resistance determinants, was investigated in a total of 57 isolates obtained from a tertiary care hospital in Japan. All of the pediatric isolates and 76.6% of the adult isolates did not belong to PCV13 (a 13-valent pneumococcal conjugate vaccine) serotypes, and 70.2% of all isolates showed multidrug resistance. All of the isolates had ply, pavA, nanA, and nanB, and high prevalence was noted for the pspA and pspC genes (96.5% and 78.9%, respectively). Detection rates for the pneumococcal histidine triad protein (Pht) genes phtA, phtB, phtD, and phtE were 49.1%, 26.3%, 61.4%, and 100%, respectively. Two fusion-type genes, phtA/B and phtA/D, were identified, with a prevalence of 36.9% and 14.0%, respectively. These fusion types showed 78.1–90.0% nucleotide sequence identity with phtA, phtB, and phtD. The most prevalent pht profile was phtA + phtD + phtE (26.3%), followed by phtA/B + phtE (19.3%) and phtA/B + phtD + phtE (17.5%), while pht profiles including phtD and/or phtA/phtD were found in 71.9% of isolates. The present study revealed the presence of two fusion types of Pht and their unexpectedly high prevalence. These fusion types, as well as PhtA and PhtB, contained sequences similar to the B cell epitopes that have been previously reported for PhtD.

Epidemiology Characteristics of Streptococcus pneumoniae From Children With Pneumonia in Shanghai: A Retrospective Study

Background: Streptococcus pneumoniae is the most common pathogen causing death in children under 5 years old. This retrospective surveillance aimed to analyze serotype distribution, drug resistance, virulence factors, and molecular characteristics of pneumonia isolates from children in Shanghai, China. Methods: A total of 287 clinical pneumococcal isolates were collected from January to December in 2018 and were divided into community-acquired pneumonia (CAP) and healthcare-associated pneumonia (HAP) two groups according to where someone contracts the infection. All isolates were serotyped by multiplex sequential PCR and antimicrobial susceptibility testing was performed using E-test or disk diffusion method. The molecular epidemiology was analyzed using multilocus sequence typing and seven housekeeping genes were sequenced to identified the sequence types (STs). In addition, we investigated the presence of virulence genes via PCR. Results: The most common serotypes were 19F, 6A, 19A, 23F, 14, and 6B, and the coverage rates of the 7-, 10- and 13-valent pneumococcal conjugate vaccines were 58.9, 58.9, and 80.5%, respectively. More PCV13/non-PCV7 serotypes and higher rate of penicillin non-susceptible S. pneumoniae were seen in HAP. Molecular epidemiological typing showed a high level of diversity and five international antibiotic-resistant clones were found, including Taiwan^19F-14, Spain^23F-1, Spain^6B-2, Taiwan^23F-15 and Sweden^15A-25. No significant difference was observed in the presence of virulence genes among the isolates obtained from CAP and HAP. All of the S. pneumoniae isolates carried lytA, ply, psaA, pavA, spxB, htrA, and clpP, and the carriage rate of nanA and piaA were 96.2 and 99.0%. Conversely, cps2A, cbpA, and pspA were present in 33.8-44.3% of the isolates. Conclusions: Serotype changes and emerging multidrug-resistant international clones were found in current study. lytA, ply, psaA, pavA, spxB, htrA, and clpP may be good protein vaccine candidates. Long-term high-quality surveillance should be conducted to assess impact and effectiveness brought by vaccines, and provide a foundation for prevention strategies and vaccine policies.

Serotype-Independent Protection Against Invasive Pneumococcal Infections Conferred by Live Vaccine With lgt Deletion

Streptococcus pneumoniae is the most common respiratory bacterial pathogen among cases of community-acquired infection in young children, older adults, and individuals with underlying medical conditions. Although capsular polysaccharide-based pneumococcal vaccines have contributed to significant decrease in invasive pneumococcal infections, these vaccines have some limitations, including limited serotype coverage, lack of effective mucosal antibody responses, and high costs. In this study, we investigated the safety and immunogenicity of a live, whole-cell pneumococcal vaccine constructed by deleting the gene for prolipoprotein diacylglyceryl transferase (lgt) from the encapsulated pneumococcal strain TIGR4 (TIGR4Δlgt) for protection against heterologous pneumococcal strains. Pneumococcal strain TIGR4 was successfully attenuated by deletion of lgt, resulting in the loss of inflammatory activity and virulence. TIGR4Δlgt colonized the nasopharynx long enough to induce strong mucosal IgA and IgG2b-dominant systemic antibody responses that were cross-reactive to heterologous pneumococcal serotypes. Finally, intranasal immunization with TIGR4Δlgt provided serotype-independent protection against pneumococcal challenge in mice. Taken together, our results suggest that TIGR4Δlgt is an avirulent and attractive broad-spectrum pneumococcal vaccine candidate. More broadly, we assert that modulation of such "master" metabolic genes represents an emerging strategy for developing more effective vaccines against numerous infectious agents.

Assessing the function of pneumococcal neuraminidases NanA, NanB and NanC in in vitro and in vivo lung infection models using monoclonal antibodies

Streptococcus pneumoniae isolates express up to three neuraminidases (sialidases), NanA, NanB and NanC, all of which cleave the terminal sialic acid of glycan-structures that decorate host cell surfaces. Most research has focused on the role of NanA with limited investigations evaluating the roles of all three neuraminidases in host-pathogen interactions. We generated two highly potent monoclonal antibodies (mAbs), one that blocks the enzymatic activity of NanA and one cross-neutralizing NanB and NanC. Total neuraminidase activity of clinical S. pneumoniae isolates could be inhibited by this mAb combination in enzymatic assays. To detect desialylation of cell surfaces by pneumococcal neuraminidases, primary human tracheal/bronchial mucocilial epithelial tissues were infected with S. pneumoniae and stained with peanut lectin. Simultaneous targeting of the neuraminidases was required to prevent desialylation, suggesting that inhibition of NanA alone is not sufficient to preserve terminal lung glycans. Importantly, we also found that all three neuraminidases increased the interaction of S. pneumoniae with human airway epithelial cells. Lectin-staining of lung tissues of mice pre-treated with mAbs before intranasal challenge with S. pneumoniae confirmed that both anti-NanA and anti-NanBC mAbs were required to effectively block desialylation of the respiratory epithelium in vivo. Despite this, no effect on survival, reduction in pulmonary bacterial load, or significant changes in cytokine responses were observed. This suggests that neuraminidases have no pivotal role in this murine pneumonia model that is induced by high bacterial challenge inocula and does not progress from colonization as it happens in the human host.