Vaccination with the immunoglobulin M-degrading enzyme of Streptococcus suis, Ide Ssuis, leads to protection against a highly virulent serotype 9 strain

Comparative analysis of the interactions of different Streptococcus suis strains with monocytes, granulocytes and the complement system in porcine blood

Streptococcus suis (S. suis) is an important porcine pathogen causing meningitis, arthritis, and septicemia. Serotypes 2 and 14 are the most common zoonotic ones worldwide, whereas serotypes 2, 9, and 7 are very important in pigs in Europe. To cause invasive infections S. suis needs to enter the bloodstream. Consequently, the immune response in blood represents an important line of defense and bacteremia plays a key role in the pathogenesis of invasive S. suis infections. We investigated the working hypothesis that S. suis strains of the same serotype but different clonal complex (CC) might exhibit substantial differences in the interaction with components of the immune system in porcine blood. The experimental design of this study includes comparative analysis of 8 virulent strains belonging to 4 serotypes with strains of the same serotype being genetically not closely related. Significant differences between two strains of the same serotype but different clonal complex were recorded in the flow cytometric analysis of association with different leukocytes for serotype 9 and 14. Our results demonstrate that the serotype 9 strain of CC94 shows significantly increased association with monocytes and survival in porcine blood of conventional piglets as well as a tendency towards decreased composition of C3 in plasma of these piglets in comparison to the serotype 9 strain of CC16. Correlation analysis of C3 deposition on the bacterial surface and survival in respective blood samples of 8-week-old piglets demonstrated a negative correlation indicating that C3 deposition is a crucial step to limit bacterial survival and proliferation of different S. suis pathotypes in the blood of these piglets. In summary, our results indicate that the capsule composition of a S. suis strain is not alone sufficient to determine association with leukocytes, activation of complement, induction of proinflammatory cytokines, oxidative burst, and bacterial survival in porcine blood. In this study, substantial differences in these host-pathogen interactions were observed between strains of the same serotype. Therefore, a more comprehensive characterization of the field isolates, including at least MLST analysis to determine the sequence type/clonal complex, is recommended.

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.

Immunoglobulin M-degrading enzyme of Streptococcus suis (Ide Ssuis ) impairs porcine B cell signaling

Streptococcus suis (S. suis) is an important porcine pathogen, causing severe disease like meningitis and septicemia primarily in piglets. Previous work showed that the IgM-degrading enzyme of S. suis (Ide _Ssuis ) specifically cleaves soluble porcine IgM and is involved in complement evasion. The objective of this study was to investigate Ide _Ssuis cleavage of the IgM B cell receptor and subsequent changes in B cell receptor mediated signaling. Flow cytometry analysis revealed cleavage of the IgM B cell receptor by recombinant (r) Ide _Ssuis _homologue as well as Ide _Ssuis derived from culture supernatants of S. suis serotype 2 on porcine PBMCs and mandibular lymph node cells. Point-mutated rIde _Ssuis _homologue_C195S did not cleave the IgM B cell receptor. After receptor cleavage by rIde _Ssuis _homologue, it took at least 20 h for mandibular lymph node cells to restore the IgM B cell receptor to levels comparable to cells previously treated with rIde _Ssuis _homologue_C195S. B cell receptor mediated signaling after specific stimulation via the F(ab')₂ portion was significantly inhibited by rIde _Ssuis _homologue receptor cleavage in IgM⁺ B cells, but not in IgG⁺ B cells. Within IgM⁺ cells, CD21⁺ B2 cells and CD21^- B1-like cells were equally impaired in their signaling capacity upon rIde _Ssuis _homologue B cell receptor cleavage. In comparison, intracellular B cell receptor independent stimulation with tyrosine phosphatase inhibitor pervanadate increased signaling in all investigated B cell types. In conclusion, this study demonstrates Ide _Ssuis cleavage efficacy on the IgM B cell receptor and its consequences for B cell signaling.

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.

Clinical and pathological aspects of an outbreak of Streptococcus suis serotype 9 infection in pigs

ABSTRACT: Streptococcus suis is a Gram-positive pathogen that inhabits the upper respiratory tract and can cause severe systemic inflammatory disease in pigs, mainly during the nursery phase. Streptococcus suis is a reemergent pathogen, and outbreaks of its inducing disease represent significant economic losses for the pig industry worldwide. In this study, we described the clinical, pathological, and molecular aspects of an outbreak of S. suis infection with atypically high mortality. The outbreak occurred in nursery farms integrated into a cooperative in the state of Paraná, Brazil. Of the 30 nurseries, 10 were severely affected by the pathogen and had high economic losses. Clinical signs usually started approximately 10 days after weaning and were mainly characterized by acute nervous and locomotor disorders. The mortality of the affected batches usually ranged between 8% and 10%, but in some cases, it reached 18%. Nine piglets were submitted to post mortem examination. Macroscopically, the synovial joints were enlarged and contained fibrinous exudates. In the central nervous system, there was hyperemia of the leptomeningeal vessels associated with deposition of fibrin and purulent exudate in the leptomeninges. In three piglets, there was thickening of the choroid plexus associated with dilation of the lateral ventricles. Microscopic lesions were characterized mainly by fibrinosuppurative inflammation, which involved the synovial membranes, leptomeninges of the brain, and spinal cord. Furthermore, it also affects the choroid plexus, ependyma, nerve roots, and central canal of the spinal cord. S. suis was isolated from the cerebrospinal fluid, meningeal swabs, and/or synovial fluid of 8/9 piglets, and typified as serotype 9 by multiplex PCR.

Immunogenicity and protective efficacy of a Streptococcus suis vaccine composed of six conserved immunogens

A vaccine protecting against different Streptococcus suis serotypes is highly needed in porcine practice to improve animal welfare and reduce the use of antibiotics. We hypothesized that immunogens prominently recognized by convalescence sera but significantly less so by sera of susceptible piglets are putative protective antigens. Accordingly, we investigated immunogenicity and protective efficacy of a multicomponent vaccine including six main conserved immunogens, namely SSU0934, SSU1869, SSU0757, SSU1950, SSU1664 and SSU0187. Flow cytometry confirmed surface expression of all six immunogens in S. suis serotypes 2, 9 and 14. Although prime-booster vaccination after weaning resulted in significantly higher specific IgG levels against all six immunogens compared to the placebo-treated group, no significant differences between bacterial survival in blood from either vaccinated or control animals were recorded for serotype 2, 9 and 14 strains. Furthermore, vaccinated piglets were not protected against morbidity elicited through intranasal challenge with S. suis serotype 14. As ~50% of animals in both groups did not develop disease, we investigated putative other correlates of protection. Induction of reactive oxygen species (ROS) in blood granulocytes was not associated with vaccination but correlated with protection as all piglets with >5% ROS survived the challenge. Based on these findings we discuss that the main immunogens of S. suis might actually not be a priori good candidates for protective antigens. On the contrary, expression of immunogens that evoke antibodies that do not mediate killing of this pathogen might constitute an evolutionary advantage conserved in many different S. suis strains.

Survival patterns of Streptococcus suis serotypes 1 and 14 in porcine blood indicate cross-reactive bactericidal antibodies in naturally infected pigs

Streptococcus suis serotype (cps) 1 and cps14 have been detected in association with severe diseases such as meningitis and polyarthritis in pigs. Though these two cps are very similar, only cps14 is an important zoonotic agent in Asia and only cps1 is described to be associated with diseases in suckling piglets rather than weaning piglets. The main objective of this study was to assess restriction of survival of cps14 and cps1 in porcine blood by IgG and IgM putatively cross-reacting with these two cps. Furthermore, we differentiate recent European cps1/14 strains by agglutination, cpsK sequencing, MLST and virulence-associated gene profiling. Our data confirmed cps1 of clonal complex 1 as an important pathotype causing polyarthritis in suckling piglets in Europe. The experimental design included also bactericidal assays with blood samples drawn at different ages of piglets naturally infected with different S. suis cps types including cps1 but not cps14. We report survival of a cps1 and a cps14 strain (both of sequence type 1) in blood of suckling piglets with high levels of maternal IgG binding to the bacterial surface. In contrast, killing of cps1 and cps14 was recorded in older piglets due to an increase of IgM as demonstrated by specific cleavage of IgM. Heterologous absorption of antibodies with cps1 or cps14 is sufficient to significantly increase the survival of the other cps. In conclusion, IgM elicited by natural S. suis infection is crucial for killing of S. suis cps1 and cps14 in older weaning piglets and has most likely the potential to cross-react between cps1 and cps14.

Complete Genome Sequences of Streptococcus suis Pig-Pathogenic Strains 10, 13-00283-02, and 16085/3b

Streptococcus suis is an important pathogen of pigs that, as a zoonotic agent, can also cause severe disease in humans, including meningitis, endocarditis, and septicemia. We report complete and annotated genomes of S. suis strains 10, 13-00283-02, and 16085/3b, which represent the highly prevalent serotypes cps2, cps7, and cps9, respectively.

Streptococcus suis is an important pathogen of pigs that, as a zoonotic agent, can also cause severe disease in humans, including meningitis, endocarditis, and septicemia. We report complete and annotated genomes of S. suis strains 10, 13-00283-02, and 16085/3b, which represent the highly prevalent serotypes cps2, cps7, and cps9, respectively.

Update on Streptococcus suis Research and Prevention in the Era of Antimicrobial Restriction: 4th International Workshop on S. suis

Streptococcus suis is a swine pathogen and a zoonotic agent afflicting people in close contact with infected pigs or pork meat. Sporadic cases of human infections have been reported worldwide. In addition, S. suis outbreaks emerged in Asia, making this bacterium a primary health concern in this part of the globe. In pigs, S. suis disease results in decreased performance and increased mortality, which have a significant economic impact on swine production worldwide. Facing the new regulations in preventive use of antimicrobials in livestock and lack of effective vaccines, control of S. suis infections is worrisome. Increasing and sharing of knowledge on this pathogen is of utmost importance. As such, the pathogenesis and epidemiology of the infection, antimicrobial resistance, progress on diagnosis, prevention, and control were among the topics discussed during the 4th International Workshop on Streptococcus suis (held in Montreal, Canada, June 2019). This review gathers together recent findings on this important pathogen from lectures performed by lead researchers from several countries including Australia, Canada, France, Germany, Japan, Spain, Thailand, The Netherlands, UK, and USA. Finally, policies and recommendations for the manufacture, quality control, and use of inactivated autogenous vaccines are addressed to advance this important field in veterinary medicine.

Analysis of Porcine Pro- and Anti-Inflammatory Cytokine Induction by S. suis In Vivo and In Vitro

Weaning piglets are susceptible to the invasive Streptococcus (S.) suis infection, which can result in septicemia. The aim of this study was to investigate the cytokine profile induced upon S. suis infection of blood, to determine the cellular sources of those cytokines, and to study the potential effects of the induced cytokines on bacterial killing. We measured TNF-α, IL-6, IFN-γ, IL-17A and IL-10 after an experimental intravenous infection with S. suis serotype 2 in vivo, and analyzed whole blood, peripheral blood mononuclear cells (PBMC) and separated leukocytes to identify the cytokine-producing cell type(s). In addition, we used a reconstituted whole blood assay to investigate the effect of TNF-α on bacterial killing in the presence of different S. suis-specific IgG levels. An increase in IL-6 and IL-10, but not in IFN-γ or IL-17A, was observed in two of three piglets with pronounced bacteremia 16 to 20 h after infection, but not in piglets with controlled bacteremia. Our results confirmed previous findings that S. suis induces TNF-α and IL-6 and could demonstrate that TNF-α is produced by monocytes in vitro. We further found that IL-10 induction resulted in reduced secretion of TNF-α and IL-6. Rapid induction of TNF-α was, however, not crucial for in vitro bacterial killing, not even in the absence of specific IgG.