Evaluation of immune effect of Streptococcus suis biofilm-associated protein PDH

Evaluation of the protective efficacy of three novel identified membrane associated proteins of Streptococcus suis serotype 2

Streptococcus suis is one of the major pathogens of pigs circulating worldwide, and the development of vaccines will help to effectively control streptococcosis in swine. In this study, we evaluated the potential of three membrane associated proteins, histidine kinase (HK), glycosyltransferase family 2 (Gtf-2) and phosphate binding protein (PsbP) of S. suis as subunit vaccines. Bioinformatics analysis shows that protein ABC is highly conserved in S. suis. To verify the protective effects of these proteins in animal models, recombinant protein HK, Gtf-2 and PsbP were used to immunize BALB/c mice separately. The results showed that these proteins immunization in mice can effectively induce strong humoral immune responses, protect mice from cytokine storms caused by S. suis infection, and have a significant protective effect against lethal doses of S. suis infection. Furthermore, antibodies with opsonic activity exist in the recombinant proteins antiserum to assist phagocytic cells in killing S. suis. Overall, these results indicated that these recombinant proteins all elicit good immune protective effect against S. suis infection and can be represent promising candidate antigens for subunit vaccines against S. suis.

Lipoteichoic acids influence cell shape and bacterial division of Streptococcus suis serotype 2, but play a limited role in the pathogenesis of the infection

Streptococcus suis serotype 2 is a major swine pathogen and a zoonotic agent, causing meningitis in both swine and humans, responsible for substantial economic losses to the swine industry worldwide. The pathogenesis of infection and the role of bacterial cell wall components in virulence have not been fully elucidated. Lipoproteins, peptidoglycan, as well as lipoteichoic acids (LTA) have all been proposed to contribute to virulence. In the present study, the role of the LTA in the pathogenesis of the infection was evaluated through the characterisation of a mutant of the S. suis serotype 2 strain P1/7 lacking the LtaS enzyme, which mediates the polymerization of the LTA poly-glycerolphosphate chain. The ltaS mutant was confirmed to completely lack LTA and displayed significant morphological defects. Although the bacterial growth of this mutant was not affected, further results showed that LTA is involved in maintaining S. suis bacterial fitness. However, its role in the pathogenesis of the infection appears limited. Indeed, LTA presence reduces self-agglutination, biofilm formation and even dendritic cell activation, which are important aspects of the pathogenesis of the infection caused by S. suis. In addition, it does not seem to play a critical role in virulence using a systemic mouse model of infection.

Rethinking the control of Streptococcus suis infection: Biofilm formation

Streptococcus suis is an emerging zoonotic pathogen that is widespread in swine populations. The control of S. suis infection and its associated diseases is a daunting challenge worldwide. Biofilm formation appears to be the main reason for the persistence of S. suis. In this review we gather existing knowledge on S. suis biofilm, describing the role of biofilm formation in S. suis virulence and drug resistance, the regulatory factors of S. suis biofilm formation, and the research progress of inhibiting S. suis biofilm formation, with the aim of providing guidance for future studies related to the field of S. suis biofilms.

Development of a Universal Multi-Epitope Vaccine Candidate against Streptococcus suis Infections Using Immunoinformatics Approaches

Streptococcus suis is a significant zoonotic pathogen that is a great threat not only to the swine industry but also to human health, causing arthritis, meningitis, and even streptococcal toxic shock-like syndrome. Owing to its many serotypes and high geographic variability, an efficacious cross-protective S. suis vaccine is not readily available. Therefore, this study aimed to design a universal multi-epitope vaccine (MVHP6) that involved three highly immunogenic proteins of S. suis, namely, the surface antigen containing a glycosaminoglycan binding domain (HP0197), endopeptidase (PepO), and 6-phosphogluconate dehydrogenase (6PGD). Forecasted T-cell and B-cell epitopes with high antigenic properties and a suitable adjuvant were linked to construct a multi-epitope vaccine. In silico analysis showed that the selected epitopes were conserved in highly susceptible serotypes for humans. Thereafter, we evaluated the different parameters of MVHP6 and showed that MVHP6 was highly antigenic, non-toxic, and non-allergenic. To verify whether the vaccine could display appropriate epitopes and maintain high stability, the MVHP6 tertiary structure was modeled, refined, and validated. Molecular docking studies revealed a strong binding interaction between the vaccine and the toll-like receptor (TLR4), whereas molecular dynamics simulations demonstrated the vaccine's compatibility, binding stability, and structural compactness. Moreover, the in silico analysis showed that MVHP6 could evoke strong immune responses and enable worldwide population coverage. Moreover, MVHP6 was cloned into the pET28a (+) vector in silico to ensure the credibility, validation, and proper expression of the vaccine construct. The findings suggested that the proposed multi-epitope vaccine can provide cross-protection against S. suis infections.

GrpE and ComD contribute to the adherence, biofilm formation, and pathogenicity of Streptococcus suis

Streptococcus suis is a major bacterial pathogen of swine and an emerging zoonotic agent that has to date resulted in substantial economic losses to the swine industry worldwide, and can cause persistent infection by forming biofilms. GrpE and histidine protein kinase ComD are important proteins implicated in the pathogenicity of S. suis, although whether they play roles in adhesion and biofilm formation has yet to be sufficiently clarified. In this study, we constructed grpE and comD deletion strains of S. suis by homologous recombination, and examined their cell adhesion and biofilm formation capacities compared with those of the wild-type strain. The pathogenicity of the grpE and comD deletion strains was evaluated using a mouse infection model, which revealed that compared with the wild-type, these deletion strains induced milder symptoms and lower bacteremia, as well as comparatively minor organ (brain, spleen, liver, and lung) lesions, in the infected mice. Moreover, the deletion of grpE and comD significantly reduced the pro-inflammatory cytokine (IL-6, IL-1β, and TNF-α) induction capacity of S. suis. Collectively, the findings of this study indicate that the GrpE and ComD proteins of Streptococcus suis play key roles in the adherence to PK-15 cells and the formation of biofilms, thereby contributing to the virulence of this pathogen.