Vaccination with Streptococcus suis serotype 2 recombinant 6PGD protein provides protection against S. suis infection in swine

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.

A critical review on experimental Streptococcus suis infection in pigs with a focus on clinical monitoring and refinement strategies

Streptococcus suis (S. suis) is a major pig pathogen worldwide with zoonotic potential. Though different research groups have contributed to a better understanding of the pathogenesis of S. suis infections in recent years, there are still numerous neglected research topics requiring animal infection trials. Of note, animal experiments are crucial to develop a cross-protective vaccine which is highly needed in the field. Due to the severe clinical signs associated with S. suis pathologies such as meningitis and arthritis, implementation of refinement is very important to reduce pain and distress of experimentally infected pigs. This review highlights the great diversity of clinical signs and courses of disease after experimental S. suis pig infections. We review clinical read out parameters and refinement strategies in experimental S. suis pig infections published between 2000 and 2021. Currently, substantial differences exist in describing clinical monitoring and humane endpoints. Most of the reviewed studies set the body temperature threshold of fever as high as 40.5°C. Monitoring intervals vary mainly between daily, twice a day and three times a day. Only a few studies apply scoring systems. Published scoring systems are inconsistent in their inclusion of parameters such as body temperature, feeding behavior, and respiratory signs. Locomotion and central nervous system signs are more common clinical scoring parameters in different studies by various research groups. As the heterogenicity in clinical monitoring limits the comparability between studies we hope to initiate a discussion with this review leading to an agreement on clinical read out parameters and monitoring intervals among S. suis research groups.

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.

Live attenuated Salmonella enterica serovar Choleraesuis vector delivering a conserved surface protein enolase induces high and broad protection against Streptococcus suis serotypes 2, 7, and 9 in mice

Streptococcus suis, a major zoonotic pathogen in swine, can be classified into 35 serotypes. However, no universal vaccine against the multiple serotypes of S. suis is available, though some studies have shown homologous protection. Hence, developing an effective universal vaccine to protect pigs against multiple S. suis serotypes is necessary, or at the very least, to protect pigs against diseases caused by the dominant pathogenic serotypes. Enolase, a highly conserved surface protein, is present in all of the described S. suis serotypes. rSC0016 is an improved recombinant attenuated S. Choleraesuis vaccine vector, combining a sopB mutation with regulated delayed systems, achieving an adequate balance between host safety and immunogenicity. In order to develop a universal vaccine against the multiple serotypes of S. suis, a novel recombinant vaccine strain rSC0016 that carries a heterologous antigen enolase was developed in this study. According, it was found that the recombinant vaccine strain rSC0016(pS-Enolase) exhibited better colonization compared to the vaccine control strain rSC0018(pYA3493). In addition, a mouse model immunized with the strain rSC0016(pS-Enolase) elicited significant IgG antibody responses against both enolase and Salmonella antigens, while inducing good mucosal, humoral, and cellular immune responses against enolase. Finally, immunization with rSC0016(pS-Enolase) was shown to confer 100%, 80%, and 100% protection against the serotypes of SS2, SS7, and SS9, respectively, and significantly reduced histopathological lesions in mice. Overall, this study provides a promising universal vaccine candidate for use against the multiple serotypes of S. suis.

The Redox-Sensing Regulator Rex Contributes to the Virulence and Oxidative Stress Response of Streptococcus suis Serotype 2

Streptococcus suis serotype 2 (SS2) is an important zoonotic pathogen responsible for septicemia and meningitis. The redox-sensing regulator Rex has been reported to play critical roles in the metabolism regulation, oxidative stress response, and virulence of various pathogens. In this study, we identified and characterized a Rex ortholog in the SS2 virulent strain SS2-1 that is involved in bacterial pathogenicity and stress environment susceptibility. Our data show that the Rex-knockout mutant strain Δrex exhibited impaired growth in medium with hydrogen peroxide or a low pH compared with the wildtype strain SS2-1 and the complementary strain CΔrex. In addition, Δrex showed a decreased level of survival in whole blood and in RAW264.7 macrophages. Further analyses revealed that Rex deficiency significantly attenuated bacterial virulence in an animal model. A comparative proteome analysis found that the expression levels of several proteins involved in virulence and oxidative stress were significantly different in Δrex compared with SS2-1. Electrophoretic mobility shift assays revealed that recombinant Rex specifically bound to the promoters of target genes in a manner that was modulated by NADH and NAD⁺. Taken together, our data suggest that Rex plays critical roles in the virulence and oxidative stress response of SS2.

Salmonella enterica serovar Choleraesuis vector delivering SaoA antigen confers protection against Streptococcus suis serotypes 2 and 7 in mice and pigs

Streptococcus suis is one of the major pathogens that cause economic losses in the swine industry worldwide. However, current bacterins only provide limited prophylactic protection in the field. An ideal vaccine against S. suis should protect pigs against the clinical diseases caused by multiple serotypes, or at least protect against the dominant serotype in a given geographic region. A new recombinant Salmonella enterica serotype Choleraesuis vaccine vector, rSC0011, that is based on the regulated delayed attenuation system and regulated delayed antigen synthesis system, was developed recently. In this study, an improved recombinant attenuated Salmonella Choleraesuis vector, rSC0016, was developed by incorporating a sopB mutation to ensure adequate safety and maximal immunogenicity. In the spleens of mice, rSC0016 colonized less than rSC0011. rSC0016 and rSC0011 colonized similarly in Peyer's patches of mice. The recombinant vaccine rSC0016(pS-SaoA) induced stronger cellular, humoral, and mucosal immune responses in mice and swine against SaoA, a conserved surface protein that is present in many S. suis serotypes, than did rSC0011(pS-SaoA) without sopB or rSC0018(pS-SaoA), which is an avirulent, chemically attenuated vaccine strain. rSC0016(pS-SaoA) provided 100% protection against S. suis serotype 2 in mice and pigs, and full cross-protection against SS7 in pigs. This new vaccine vector provides a foundation for the development of a universal vaccine against multiple serotypes of S. suis in pigs.

Streptococcus suis vaccines: candidate antigens and progress

Streptococcus suis is a major swine pathogen and an emerging zoonotic agent of human meningitis and streptococcal toxic shock-like syndrome. S. suis is a well-encapsulated pathogen and multiple serotypes have been described based on the capsular polysaccharide antigenic diversity. In addition, high genotypic, phenotypic and geographic variability exits among strains within the same serotype. Besides, S. suis uses an arsenal of virulence factors to evade the host immune system. Together, these characteristics have challenged the development of efficacious vaccines to fight this important pathogen. In this careful and comprehensive review, clinical field information and experimental data have been compiled and compared for the first time to give a precise overview of the current status of vaccine development against S. suis. The candidate antigens and vaccine formulations under research are examined and the feasibility of reaching the goal of a "universal" cross-protective S. suis vaccine discussed.

The fibronectin-binding protein Fnm contributes to adherence to extracellular matrix components and virulence of Enterococcus faecium

The interaction between bacteria and fibronectin is believed to play an important role in the pathogenicity of clinically important Gram-positive cocci. In the present study, we identified a gene encoding a predicted fibronectin-binding protein of Enterococcus faecium (fnm), a homologue of Streptococcus pneumoniae pavA, in the genomes of E. faecium strain TX82 and all other sequenced E. faecium isolates. Full-length recombinant Fnm from strain TX82 bound to immobilized fibronectin in a concentration-dependent manner and also appeared to bind collagen type V and laminin, but not other proteins, such as transferrin, heparin, bovine serum albumin, mucin, or collagen IV. We demonstrated that the N-terminal fragment of Fnm is required for full fibronectin binding, since truncation of this region caused a 2.4-fold decrease (P < 0.05) in the adhesion of E. faecium TX82 to fibronectin. Deletion of fnm resulted in a significant reduction (P < 0.001) in the ability of the mutant, TX6128, to bind fibronectin relative to that of the wild-type strain; in situ reconstitution of fnm in the deletion mutant strain restored adherence. In addition, the Δfnm mutant was highly attenuated relative to TX82 (P ≤ 0.0001) in a mixed-inoculum rat endocarditis model. Taken together, these results demonstrate that Fnm affects the adherence of E. faecium to fibronectin and is important in the pathogenesis of experimental endocarditis.

Live attenuated Salmonella enterica serovar Choleraesuis vaccine vector displaying regulated delayed attenuation and regulated delayed antigen synthesis to confer protection against Streptococcus suis in mice

Salmonella enterica serotype Choleraesuis (S. Choleraesuis) and Streptococcus suis (S. suis) are important swine pathogens. Development of a safe and effective attenuated S. Choleraesuis vaccine vector would open a new window to prevent and control pig diseases. To achieve this goal, the mannose and arabinose regulated delayed attenuated systems (RDAS), Δpmi and ΔPcrp::TT araC PBADcrp, were introduced into the wild type S. Choleraesuis strain C78-3. We also introduced ΔrelA::araC PBADlacI TT to achieve regulated delayed antigen synthesis and ΔasdA to constitute a balanced-lethal plasmid system. The safety and immunogenicity of the resulted RDAS S. Choleraesuis strain rSC0011 carrying 6-phosphogluconate dehydrogenase (6-PGD) of S. suis serotype 2 (SS2) were evaluated in vitro and in vivo. Compared with the wild type parent strain C78-3 and vaccine strain C500, a live attenuated S. Choleraesuis vaccine licensed for piglet in China, the results showed that the survival curves of the vaccine strain rSC0011 were similar to those of strains C78-3 and C500 at the early stage of infection, but lower than those of C78-3 and higher than those of C500 at the later stage in both porcine alveolar macrophages and peripheral porcine monocytes. The LD50 of the RDAS strains rSC0011 by oral route in mice was close to that of C500 and 10,000-fold higher than that of C78-3. Similar results were achieved by intraperitoneal (i.p.) route, suggesting that the RDAS strains rSC0011 achieved similar attenuation as C500. However, the RDAS strain rSC0011 was superior to C500 in colonization of Peyer's patches. Adult mice orally immunized with strain rSC0011 carrying a plasmid expression 6-phosphogluconate dehydrogenase (6-PGD) gene from SS2 developed strong immune responses against 6-PGD and Salmonella antigens, and conferred high protection against i.p. challenge with SS2.

Streptococcus suis infection: an emerging/reemerging challenge of bacterial infectious diseases?

Streptococcus suis (S. suis) is a family of pathogenic gram-positive bacterial strains that represents a primary health problem in the swine industry worldwide. S. suis is also an emerging zoonotic pathogen that causes severe human infections clinically featuring with varied diseases/syndromes (such as meningitis, septicemia, and arthritis). Over the past few decades, continued efforts have made significant progress toward better understanding this zoonotic infectious entity, contributing in part to the elucidation of the molecular mechanism underlying its high pathogenicity. This review is aimed at presenting an updated overview of this pathogen from the perspective of molecular epidemiology, clinical diagnosis and typing, virulence mechanism, and protective antigens contributing to its zoonosis.

Surface-associated and secreted factors ofStreptococcus suisin epidemiology, pathogenesis and vaccine development

Streptococcus suisis an invasive porcine pathogen associated with meningitis, arthritis, bronchopneumonia and other diseases. The pathogen constitutes a major health problem in the swine industry worldwide. Furthermore,S. suisis an important zoonotic agent causing meningitis and other diseases in humans exposed to pigs or pork. Current knowledge on pathogenesis is limited, despite the enormous amount of data generated by ‘omics’ research. Accordingly, immunprophylaxis (in pigs) is hampered by lack of a cross-protective vaccine against virulent strains of this diverse species. This review focuses on bacterial factors, both surface-associated and secreted ones, which are considered to contribute toS. suisinteraction(s) with host factors and cells. Factors are presented with respect to (i) their identification and features, (ii) their distribution amongS. suisand (iii) their significance for virulence, immune response and vaccination. This review also shows the enormous progress made in research onS. suisover the last few years, and it emphasizes the numerous challenging questions remaining to be answered in the future.