Immunization with Streptococcus suis bacterin plus recombinant Sao protein in sows conveys passive immunity to their piglets

Immunogenicity and Protective Capacity of Sugar ABC Transporter Substrate-Binding Protein against Streptococcus suis Serotype 2, 7 and 9 Infection in Mice

Background:Streptococcus suis (S. suis) is a Gram-positive bacterium that causes substantial disease in pigs. S. suis is also an emerging zoonoses in humans, primarily in Asia, through the consumption of undercooked pork and the handling of infected pig meat as well as carcasses. The complexity of S. suis epidemiology, characterized by the presence of multiple bacterial serotypes and strains with diverse sequence types, identifies a critical need for a universal vaccine with the ability to confer cross-protective immunity. Highly conserved immunogenic proteins are generally considered good candidate antigens for subunit universal vaccines. Methods: In this study, the cross-protection of the sugar ABC transporter substrate-binding protein (S-ABC), a surface-associated immunogenic protein of S. suis, was examined in mice for evaluation as a universal vaccine candidate. Results: S-ABC was shown to be highly conserved, with 97% amino acid sequence identity across 31 S. suis strains deposited in GenBank. Recombinantly expressed S-ABC (rS-ABC) was recognized via rabbit sera specific to S. suis serotype 2. The immunization of mice with rS-ABC induced antigen-specific antibody responses, as well as IFN-γ and IL-4, in multiple organs, including the lungs. rS-ABC immunization conferred high (87.5% and 100%) protection against challenges with S. suis serotypes 2 and 9, demonstrating high cross-protection against these serotypes. Protection, albeit lower (50%), was also observed in mice challenged with S. suis serotype 7. Conclusions: These data identify S-ABC as a promising antigenic target within a universal subunit vaccine against S. suis.

Preparation and Study of Bacterins

Streptococcus suis is a bacterial pathogen that can cause significant economic losses in the swine industry due to high morbidity and mortality rates in infected animals. Vaccination with bacterins, which consist of inactivated bacteria and adjuvants to enhance the pig's immune response, is an effective approach to control S. suis infections in piglets. Here we provide a description of S. suis bacterins and the methods for vaccine preparation. Moreover, this chapter also describes the addition of recombinant Sao (rSao-L) protein to the S. suis bacterin, aiming to enhance the efficacy of the bacterins against S. suis in piglets. Furthermore, the methods for evaluating the immune response elicited by the bacterins are also covered in this chapter.

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.

Bovine Herpesvirus-4 Based Vaccine Provides Protective Immunity against Streptococcus suis Disease in a Rabbit Model

Streptococcus suis (S. suis) is a bacterial pathogen of pigs that has a major animal health and economic impact on the pig industry. Bovine herpesvirus-4 (BoHV-4) is a new virus-based vaccine vector that has been used for the immunogenic delivery of antigens from a variety of pathogens. In the present study, two recombinant BoHV-4-based vectors were evaluated for their ability to induce immunity and protection against S. suis in a rabbit model. The GMD protein is a fusion protein consisting of multiple dominant B-cell epitopes ((B-cell dominant epitopes of GAPDH, MRP, and DLDH antigens) (BoHV-4/GMD)) and the second suilysin (SLY) (BoHV-4/SLY) from S. suis serotype 2 (SS2). Both GMD and SLY delivered by the BoHV-4 vectors were recognized by sera from SS2-infected rabbits. The vaccination of rabbits with the BoHV-4 vectors induced antibodies against SS2, as well as against additional S. suis serotypes, SS7 and SS9. However, sera from BoHV-4/GMD-vaccinated animals promoted a significant level of phagocytic activity by pulmonary alveolar macrophages (PAMs) against SS2, SS7, and SS9. In contrast, sera from rabbits immunized with BoHV-4/SLY induced PAM phagocytic activity against only SS2. In addition, BoHV-4 vaccines differed in the associated level of protection against lethal SS2 challenge, which ranged from high (71.4%) to low (12.5%) for BoHV-4/GMD and BoHV-4/SLY, respectively. These data suggest BoHV-4/GMD as a promising vaccine candidate against S. suis disease.

Subunit Vaccine Targeting Phosphate ABC Transporter ATP-Binding Protein, PstB, Provides Cross-Protection against Streptococcus suis Serotype 2, 7, and 9 in Mice

Streptococcus suis is a significant pathogen in pigs and a newly emerging zoonotic agent in humans. The presence of multiple serotypes and strains with diversified sequence types in pig herds highlights the need for the identification of broadly cross-reactive universal vaccine antigen targets, capable of providing cross-protection against S. suis infection. Subunit vaccines based on the conserved proteins shared between different S. suis serotypes are potential candidates for such a universally protective vaccine. In the present study, phosphate ABC transporter ATP-binding protein PstB (PstB), an immunogenic protein of the S. suis bacterium, was expressed and purified, and then subjected to cross-protection evaluation in mice. The PstB protein showed nearly 100% amino acid similarity across a panel of 31 S. suis isolates representing different serotypes, which were collected from different countries. A recombinant PstB (rPstB) protein (S. suis serotype 2) was recognized by rabbit sera specific to this serotype, and induced high levels of IFN-γ and IL-4 in mice immunized with the recombinant protein. These cytokines are considered important for protection against S. suis infection. Immunization of mice with rPstB resulted in an 87.5% protection against challenge with S. suis serotype 2 and 9 strains, suggesting a high level of cross-protection for S. suis serotypes 2 and 9. A lower protection rate (62.5%) was observed in mice challenged with the S. suis serotype 7 strain. These data demonstrate that PstB is a promising target antigen for development as a component of a universal subunit vaccine against multiple S. suis serotypes.

TbpBY167A-based vaccine is safe in pregnant sows and induces high titers of maternal derived antibodies that reduce Glaesserella parasuis colonization in piglets

Glässer's disease is one of the main diseases affecting young piglets, particularly during the nursery phase, that can significantly impact pork production. Vaccination of sows has the potential to prevent Glaesserella parasuis infection during the first weeks of life that is to a substantial degree due to the transfer of maternal derived antibodies (MDA) in colostrum. In this study we compare the antibody response to two vaccines administered to pregnant sows. A subunit vaccine containing the mutant transferrin-binding protein, TbpB^Y167A, and an autogenous vaccine formulated with the LM96/20 strain of G. parasuis (SV4) administered on days 65 and 86 of the gestational period were safe and induced high titers of antibodies in sows. The IgG peak was reached on day 100 of gestation, and the translocation of IgG to the mammary gland was confirmed in colostrum at the time of delivery. Piglets born from vaccinated sows maintained positive IgG titers against TbpB^Y167A or G. parasuis SV4 for the duration of the experiment (35 days of life). Piglets born from sows vaccinated with the TbpB^Y167A-based vaccine had a significantly (p = 0.001) lower load of G. parasuis in the respiratory tract compared to those born from sows vaccinated with the autogenous vaccine. Finally, we demonstrate that the LM96/20 (SV4) strain is highly virulent and a primary agent of Glässer's disease.

A new S. suis serotype 3 infection model in pigs: lack of effect of buprenorphine treatment to reduce distress

BACKGROUND

Streptoccocus suis (S. suis) is a major porcine pathogen causing meningitis, septicemia, arthritis and endocarditis. These diseases severely impair welfare of pigs. Experimental studies in pigs are important to better understand the pathogenesis and to identify protective antigens, as so far there is no vaccine available protecting against various serotypes (cps). Due to the severity of disease, application of appropriate refinement strategies in experimental S. suis infections is essential to reduce distress imposed on the piglets without jeopardizing the scientific output. The objectives of this study were to evaluate buprenorphine treatment as a refinement measure and serum cortisol levels as a distress read out parameter in a new S. suis cps3 infection model in pigs.

RESULTS

Intravenous application of 2 × 10⁸ CFU of S. suis cps3 (sly⁺, mrp⁺) to 6-week-old piglets led to severe morbidity in approximately 50% of the animals. Main pathological findings included suppurative meningoencephalitis and arthritis as well as fibrinosuppurative endocarditis. Buprenorphine treatment (0.05 mg/kg every 8 h) did not prevent signs of severe pain, high clinical scores, moderate to severe pathologies or high levels of serum cortisol in single severely affected piglets. Significant differences in the course of leukocytosis, induction of specific antibodies and bactericidal immunity were not recorded between groups with or w/o buprenorphine treatment. Of note, clinically unobtrusive piglets showed serum cortisol levels at 2 and 5 days post infectionem (dpi) comparable to the levels prior to infection with cps3. Cortisol levels in serum were significantly increased in piglets euthanized due to severe disease in comparison to clinically unobtrusive pigs.

CONCLUSIONS

Different clinical courses and pathologies are induced after intravenous challenge of piglets with 2 × 10⁸ CFU of this S. suis cps3 strain. The chosen protocol of buprenorphine application does not prevent severe distress in this infection model. Important parameters of the humoral immune response, such as the level of IgM binding to S. suis cps3, do not appear to be affected by buprenorphine treatment. Serum cortisol is a meaningful parameter to measure distress in piglets experimentally infected with S. suis and to evaluate refinement strategies. In this intravenous model, which includes close clinical monitoring and different humane endpoints, clinics and cortisol levels suggest convalescence in surviving piglets within 5 days following experimental infection.

The Association of Bacterin and Recombinant Proteins Induces a Humoral Response in Sheep against Caseous Lymphadenitis

In this study, we investigated the capacity of the recombinant proteins SpaC, NanH, SodC, and PLD of C. pseudotuberculosis to trigger protective humoral and cellular immune responses against experimentally induced C. pseudotuberculosis infection in sheep. The antigens were produced in a heterologous system and were purified by affinity chromatography. Nine sheep were randomly divided into three groups, which were immunized as follows: Group 1 (control)—a mix of adjuvants composed of the inactivated T1 strain of C. pseudotuberculosis and commercial Montanide™ISA 61 VG (T1M); Group 2—rSpaC, rSodC, rPLD, and T1M; Group 3—rNanH, rSodC, rPLD, and T1M. All groups were immunized twice (on days 0 and 30) and challenged on day 90 of the experiment. Humoral and cellular immune responses were evaluated by Enzyme-Linked Immunosorbent Assay (ELISA) to quantify the IgG antibodies and interferon-gamma (IFN-y). Both vaccine formulations with recombinant proteins (groups 2 and 3) could induce a significant humoral IgG immune response in sheep. The proteins rSodC, rPLD, and rNanH were more immunogenic, inducing significant levels of IgG antibodies after the first dose of the vaccine or after the challenge, maintaining constant levels until the end of the experiment. However, it was not possible to differentiate between the cellular responses induced by the vaccines. This lack of effectiveness points toward the need for further studies to improve the efficacy of this subunit-based vaccine approach.

Evaluation of the immunogenicity and protective ability of a pili subunit, SBP2', of Streptococcus suis serotype 2

Streptococcus suis is an important zoonotic pathogen that leads to huge economic losses in the swine industry. Because of the enormous genetic and phenotypic diversity within S. suis, it is necessary to develop effective vaccines to control this zoonotic pathogen. SBP2' is a major pili subunit in S. suis that belongs to an srtBCD pili cluster and has already been reported to be associated with the pathogenesis of this bacterium. In this study, we aimed to evaluate the immunogenicity and protective ability of SBP2'. The rSBP2' protein was expressed by an Escherichia coli expression system and emulsified with Montanide ISA 201 adjuvant to prepare the subunit vaccine. Through active immune assays, the results showed that rSBP2' exhibited good immunogenicity and could protect mice from a lethal dose challenge. Additionally, the qRT-PCR data showed that the transcription levels of cytokines associated with systemic symptoms caused by S. suis were decreased, indicating that immunization with rSBP2' could protect the host from cytokine storms caused by S. suis. Furthermore, the passive immune assay showed that the humoral immunity induced by rSBP2' played an important role against S. suis infection. Taken together, SBP2' could provide proper immune protection against S. suis challenge and could be a candidate for S. suis subunit vaccine. The results of this study could provide new ideas for the development of effective vaccines against S. suis.

Immunogenicity study of a Streptococcus suis autogenous vaccine in preparturient sows and evaluation of passive maternal immunity in piglets

Background

Streptococcus suis is an important pathogen that causes severe diseases mostly in weaned piglets. Only available vaccines in the field are those composed of killed bacteria (bacterins) but data about their effectiveness are missing. We report here a field study on the immunological response induced by an autogenous vaccine applied in pre-parturient sows. Using a farm with recurrent S. suis serotype 7 problems, the study was divided in three experiments: (I) Sows received the vaccine at 7 and 3 weeks pre-farrowing. (II) Replacement gilts introduced to the herd received the vaccine at 4 and 7 weeks after their entry in quarantine and a boost 3 weeks pre-farrowing. (III) Gilts from experiment II received another boost 3 weeks pre-farrowing at their 3rd/4th parity. Levels, isotype profile and opsonophagocytosis capacity of the serum antibodies induced by vaccination were evaluated in sows and maternal immunity in piglets.

Results

In sows (I), the vaccine induced a slight, albeit significant, increase in anti-S. suis total antibodies after 2 doses when compare to basal levels already present in the animals. These antibodies showed a high opsonic capacity in vitro, highlighting their potential protective capacity. A gilt vaccination program of 3 doses (II) resulted in a significant increase in anti-S. suis total antibodies. Levels of maternal immunity transferred to piglets were high at 7 days of age, but rapidly decreased by 18 days of age. A gilt vaccination program ensued a higher transfer of maternal immunity in piglets compared to control animals; nevertheless duration was not improved at 18 day-old piglets. The vaccine response in both gilts and sows was mainly composed of IgG1 subclass, which was also the main Ig transferred to piglets. IgG2 subclass was also found in piglets, but its level was not increased by vaccination. Finally, a recall IgG1 response was induced by another boost vaccination at 3rd/4th parity (III), indicating that the vaccine induced the establishment of a lasting memory response in the herd.

Conclusions

Overall, an optimal gilt/sow vaccination program might result in increased antibody responses; nevertheless duration of maternal immunity would not last long enough to protect post-weaned piglets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02774-4.

Comparative Virulence and Genomic Analysis of Streptococcus suis Isolates

Streptococcus suis is a zoonotic bacterial swine pathogen causing substantial economic and health burdens to the pork industry. Mechanisms used by S. suis to colonize and cause disease remain unknown and vaccines and/or intervention strategies currently do not exist. Studies addressing virulence mechanisms used by S. suis have been complicated because different isolates can cause a spectrum of disease outcomes ranging from lethal systemic disease to asymptomatic carriage. The objectives of this study were to evaluate the virulence capacity of nine United States S. suis isolates following intranasal challenge in swine and then perform comparative genomic analyses to identify genomic attributes associated with swine-virulent phenotypes. No correlation was found between the capacity to cause disease in swine and the functional characteristics of genome size, serotype, sequence type (ST), or in vitro virulence-associated phenotypes. A search for orthologs found in highly virulent isolates and not found in non-virulent isolates revealed numerous predicted protein coding sequences specific to each category. While none of these predicted protein coding sequences have been previously characterized as potential virulence factors, this analysis does provide a reliable one-to-one assignment of specific genes of interest that could prove useful in future allelic replacement and/or functional genomic studies. Collectively, this report provides a framework for future allelic replacement and/or functional genomic studies investigating genetic characteristics underlying the spectrum of disease outcomes caused by S. suis isolates.

Immunogenicity and protective ability of RpoE against Streptococcus suis serotype 2

AIMS

RpoE is quite immunogenic and can be used as a candidate vaccine for Streptococcus suis infection via immunoproteomics as reported in our previous studies. In this study, we aimed to verify the immunogenicity of recombinant RpoE and its protective effect against of S. suis.

METHODS AND RESULTS

The RpoE protein was successfully expressed in Escherichia coli, and the purified recombinant protein was mixed with ISA206 to prepare an S. suis subunit vaccine. Mice were immunized with the RpoE subunit vaccine and then infected with the virulent S. suis strain ZY05719. Subunit vaccine-immunized mice achieved 50% protection, less pathological damage and less bacterial distribution in each organ compared with the control mice. Furthermore, in vitro culture, showed that mouse antisera significantly (P ＜ 0·001) inhibited the growth of S. suis, and qRT-PCR results showed that RpoE successfully induced the up-regulation of IL-6 and TNF-α cytokines.

CONCLUSIONS

RpoE mice were vaccinated to obtain immune protection, which may be candidates for S. suis subunit vaccine.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study will provide new ideas for the development of safe and effective recombinant subunits vaccines for S. suis.

Protective Effect of Recombinant Proteins of Cronobacter Sakazakii During Pregnancy on the Offspring

Cronobacter sakazakii is a food-borne pathogen carried in milk powder that can cause severe bacteremia, enterocolitis, and meningitis in newborns, which can lead to death of newborns. Preventing infection by this pathogen is significant to the health of newborns. Since infants and young children are the main target group of C. sakazakii, it is considered that maternal immunity can enhance the protection of newborns. Previous studies showed that two proteins of C. sakazakii (GroEL and OmpX) exhibited high expression levels and elicited strong immune reactions, suggesting their potential as vaccine candidates. In this study, GroEL and OmpX were recombinantly expressed in Escherichia coli and purified as immunogens to immunize pregnant rats. Three days after birth, the progeny were challenged with C. sakazakii to determine the protective effect of maternal immunity on the offspring. The results showed that immunization during pregnancy decreased bacterial load in the brain and blood, reduced brain and intestine damage, and significantly increased specific antibody titers in the offspring. Immunization with the recombinant proteins significantly increased cytokine levels in the serum of the progeny. The group whose mothers were immunized with OmpX produced more IL-4, while the group whose mothers were immunized with GroEL produced more IFN-γ, indicating that the immunogens enhanced the Th2 and Th1 responses, respectively. However, although the immune response was induced by both proteins, only the offspring of the pregnant rats immunized with OmpX or OmpX/GroEL mixture showed delayed death, possibly because immunization with OmpX led to a stronger humoral immune response in the offspring, suggesting that OmpX was a better vaccine candidate than GroEL. This study first reported that exposure to C. sakazakii proteins during pregnancy could improve the offspring's ability to resist infection caused by this pathogen.

Enolase and dipeptidyl peptidase IV protein sub-unit vaccines are not protective against a lethal Streptococcus suis serotype 2 challenge in a mouse model of infection

Background

Streptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in post-weaning piglets and is also a zoonotic agent. S. suis comprises 35 different serotypes of which the serotype 2 is the most prevalent in both pigs and humans. In the absence of commercial vaccines, bacterins (mostly autogenous), are used in the field, with controversial results. In the past years, the focus has turned towards the development of sub-unit vaccine candidates. However, published results are sometimes contradictory regarding the protective effect of a same candidate. Moreover, the adjuvant used may significantly influence the protective capacity of a given antigen. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno). Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available.

Results

Results showed that among all the field strains tested, 86 and 88% were positive for the expression of the SsEno and DPPIV proteins, respectively, suggesting that they are widely expressed by strains of different serotypes. However, no protection was obtained after two vaccine doses in a CD-1 mouse model of infection, regardless of the use of four different adjuvants. Even though no protection was obtained, significant amounts of antibodies were produced against both antigens, and this regardless of the adjuvant used.

Conclusions

Taken together, these results demonstrate that S. suis DPPIV and SsEno are probably not good vaccine candidates, at least not in the conditions evaluated in this study. Further studies in the natural host (pig) should still be carried out. Moreover, this work highlights the importance of confirming results obtained by different research groups.

Isolation and identification of Streptococcus suis from sick pigs in Bali, Indonesia

Objective

Streptococcus suis (S. suis) is a causative agent for various syndromes in pigs. It can be transmitted to humans with typical symptoms of meningitis and death. Although human infections have been confirmed at Bali Referral Hospital, Indonesia, since 2014, the bacteria have not been isolated from pigs. Here, we provide confirmation of the presence of the bacteria in sick pigs in the province.

Results

Streptococcus suis was confirmed in 8 of 30 cases. The final confirmation was made using PCR and sequencing of the glutamate dehydrogenase (GDH) and recombination/repair protein (recN) gene fragments. Upon PCR serotyping, two were confirmed to be serotype 2 or 1/2. Prominent histopathological lesions of confirmed cases were meningitis, endocarditis, pericarditis, bronchopneumonia, enteritis and glomerulonephritis. The dominant inflammatory cells were neutrophils and macrophages. Further research is needed to understand the risk factors for human infection. Community awareness on the risk of contracting S. suis and vaccine development are needed to prevent human infections.