Immunogenicity and protective capacity of EF-Tu and FtsZ of Streptococcus suis serotype 2 against lethal infection

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.

Evaluation of the protective efficacy of six major immunogenic proteins of Mycoplasma Synoviae

Mycoplasma synoviae (MS) is a primary avian pathogen prevalent worldwide that causes airsacculitis and synovitis in birds. Vaccination is recommended as the most cost-effective strategy in the control of MS infection. Novel alternative vaccines are needed for eradicating and controlling MS infection in flocks. DnaK, enolase, elongation factor Tu (EF-Tu), MSPB, NADH oxidase and LP78 are the major immunogenic antigens of MS and are promising targets for subunit vaccine candidates. In the present study, genes encoding DnaK, enolase, EF-Tu, MSPB, LP78, and NADH oxidase were cloned and expressed in Escherichia coli. Enzyme-linked immunosorbent assay showed that the six recombinant proteins were recognized by convalescent sera, indicating that they were expressed during infection. Two injections of the six subunit vaccines induced a robust antibody response and increased the concentrations of IFN-γ and IL-4, especially rEnolase and rEF-Tu. The proliferation of peripheral blood lymphocytes was enhanced in all of the immunized groups. Chickens immunized with rEnolase, rEF-Tu, rLP78, and rMSPB conferred significant protection against MS infection, as indicated by significantly lower DNA copies in the trachea, lower scores of air sac lesions, and lesser tracheal mucosal thickness than that in the challenge control. Especially, rEnolase provided the best protective efficacy, followed by rEF-Tu, rMSPB, and rLP78. Our finds demonstrate that the subunit vaccines and bacterin can only reduce the lesions caused by MS infection, but not prevent colonization of the organism. Our findings may contribute to the development of novel vaccine agents against MS infection.

The protective role of chicken cathelicidin-1 against Streptococcus suis serotype 2 in vitro and in vivo

Streptococcus suis serotype 2 (SS2) is an important zoonotic pathogen with the characteristics of high mortality and morbidity, which brings great challenges to prevent and control epidemic disease in the swine industry. Cathelicidins (CATH) are antimicrobial peptides with antimicrobial and immunomodulatory activities. In this study, bactericidal and anti-inflammatory effects of chicken cathelicidin-1 (CATH-1) were investigated in vitro and in vivo against SS2 infection. The results show that CATH-1 exhibited a better bactericidal effect compared to other species' cathelicidins including chickens (CATH-2, -3, and -B1), mice (CRAMP) and pigs (PMAP-36 and PR-39), which rapidly killed bacteria in 20 min by a time-killing curve assay. Furthermore, CATH-1 destroyed the bacterial morphology and affected bacterial ultrastructure as observed under electron microscopy. Moreover, CATH-1 antibacterial activity in vivo shows that CATH-1 increased survival rate of SS2-infected mice by 60% and significantly reduced the bacterial load in the lungs, liver, spleen, blood, and peritoneal lavage as well as the release of SS2-induced inflammatory cytokines including IL-1α, IL-1β, IL-12, and IL-18. Importantly, CATH-1 did not show severe histopathological changes in mice. Further studies on the mechanism of anti-inflammatory activity show that CATH-1 not only reduced the inflammatory response through direct neutralization, but also by regulating the TLR2/4/NF-κB/ERK pathway. This study provides a scientific basis for the research and development of antimicrobial peptides as new antimicrobial agents.

Novel virulence factor Cba induces antibody-dependent enhancement (ADE) of Streptococcus suis Serotype 9 infection in a mouse model

Streptococcus suis (SS) is a zoonotic pathogen that affects the health of humans and the development of the pig industry. The SS Cba protein is a collagen adhesin, and a few of its homologs are related to the enhancement of bacterial adhesion. We compared the phenotypes of SS9-P10, SS9-P10 cba knockout strains and its complementary strains in vitro and in vivo and found that knocking out the cba gene did not affect the growth characteristics of the strain, but it significantly reduced the ability of SS to form biofilms, adhesion to host cells, phagocytic resistance to macrophages and attenuated virulence in a mouse infection model. These results indicated that Cba was a virulence related factor of SS9. In addition, Mice immunized with the Cba protein had higher mortality and more serious organ lesions after challenge, and the same was observed in passive immunization experiments. This phenomenon is similar to the antibody-dependent enhancement of infection by bacteria such as Acinetobacter baumannii and Streptococcus pneumoniae. To our knowledge, this is the first demonstration of antibody-dependent enhancement of SS, and these observations highlight the complexity of antibody-based therapy for SS infection.

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.

Extraintestinal pathogenic Escherichia coli utilizes the surface-expressed elongation factor Tu to bind and acquire iron from holo-transferrin

Extraintestinal pathogenic Escherichia coli (ExPEC) is a common anthropozoonotic pathogen that causes systemic infections. To establish infection, ExPEC must utilize essential nutrients including iron from the host. Transferrin is an important iron source for multiple bacteria. However, the mechanism by which ExPEC utilizes transferrin remains unclear. In this study, we found that iron-saturated holo-transferrin rather than iron-free apo-transferrin promoted the vitality of ExPEC in heat-inactivated human serum. The multifunctional protein Elongation factor Tu (EFTu) worked as a holo-transferrin binding protein. EFTu not only bound holo-transferrin rather than apo-transferrin but also released transferrin-related iron, with all domains of EFTu involved in holo-transferrin binding and iron release events. We also identified the surface location of EFTu on ExPEC. Overexpression of EFTu on the surface of nonpathogenic E. coli not only promoted the binding of bacteria to holo-transferrin but also facilitated the uptake of transferrin-related iron. More importantly, it significantly enhanced the survival of E. coli in heat-inactivated human serum, which was positively correlated with holo-transferrin but not apo-transferrin. Our research revealed a novel function of EFTu in binding holo-transferrin to promote iron uptake by bacteria, suggesting that EFTu was a potential virulence factor of ExPEC. In addition, our study provided research avenues into the iron acquisition and pathogenicity mechanisms of ExPEC.

Neutrophils in Streptococcus suis Infection: From Host Defense to Pathology

Streptococcus suis is a swine pathogen and zoonotic agent responsible for economic losses to the porcine industry. Infected animals may develop meningitis, arthritis, endocarditis, sepsis and/or sudden death. The pathogenesis of the infection implies that bacteria breach mucosal host barriers and reach the bloodstream, where they escape immune-surveillance mechanisms and spread throughout the organism. The clinical manifestations are mainly the consequence of an exacerbated inflammation, defined by an exaggerated production of cytokines and recruitment of immune cells. Among them, neutrophils arrive first in contact with the pathogens to combat the infection. Neutrophils initiate and maintain inflammation, by producing cytokines and deploying their arsenal of antimicrobial mechanisms. Furthermore, neutrophilic leukocytosis characterizes S. suis infection, and lesions of infected subjects contain a large number of neutrophils. Therefore, this cell type may play a role in host defense and/or in the exacerbated inflammation. Nevertheless, a limited number of studies addressed the role or functions of neutrophils in the context of S. suis infection. In this review, we will explore the literature about S. suis and neutrophils, from their interaction at a cellular level, to the roles and behaviors of neutrophils in the infected host in vivo.

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.

Intranasal Vaccination With Multiple Virulence Factors Promotes Mucosal Clearance of Streptococcus suis Across Serotypes and Protects Against Meningitis in Mice

BACKGROUND

Streptococcus suis is an emerging zoonotic agent. Its natural habitat is the tonsils, which are the main portals of S. suis entry into the bloodstream of pigs. The remarkable variability of the bacteria and complex pathogenic mechanisms make the development of a vaccine a difficult task.

METHOD

Five conserved virulence factors involved in critical events of S. suis pathogenesis were combined and used as an intranasal vaccine (V5). The effect of V5 was investigated with intranasal and systemic challenge models.

RESULTS

V5 induced antibody and T-cell responses at the mucosal site and systemically. The immunity promoted clearance of S. suis from the nasopharynx independent of S. suis serotypes and reduced lethality after systemic challenge with S. suis serotype 2. Moreover, mice that survived sepsis from intravenous infection developed meningitis, whereas none of these mice showed neuropathological symptoms after V5 receipt.

CONCLUSION

Intranasal immunization with multiple conserved virulence factors decreases S. suis colonization at the nasopharynx across serotypes and inhibits the dissemination of the bacteria in the host. The protective mucosal immunity effects would potentially reduce the S. suis reservoir and prevent S. suis disease in pigs.

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.

The Diverse Functional Roles of Elongation Factor Tu (EF-Tu) in Microbial Pathogenesis

Elongation factor thermal unstable Tu (EF-Tu) is a G protein that catalyzes the binding of aminoacyl-tRNA to the A-site of the ribosome inside living cells. Structural and biochemical studies have described the complex interactions needed to effect canonical function. However, EF-Tu has evolved the capacity to execute diverse functions on the extracellular surface of both eukaryote and prokaryote cells. EF-Tu can traffic to, and is retained on, cell surfaces where can interact with membrane receptors and with extracellular matrix on the surface of plant and animal cells. Our structural studies indicate that short linear motifs (SLiMs) in surface exposed, non-conserved regions of the molecule may play a key role in the moonlighting functions ascribed to this ancient, highly abundant protein. Here we explore the diverse moonlighting functions relating to pathogenesis of EF-Tu in bacteria and examine putative SLiMs on surface-exposed regions of the molecule.

Synergy between Th1 and Th2 responses during Mycobacterium tuberculosis infection: A review of current understanding

Induction of Th1 (cell-mediated) immunity and associated production of IFN-γ by CD4+ T cells has been widely used as a marker of protective immunity against tuberculosis (TB). This is based on two assumptions. The first is the widely accepted view that Mycobacterium tuberculosis (Mtb), the causative agent of TB is an obligate intracellular pathogen, and the second is based on the Th1/Th2 paradigm, which posits that polarization of CD4+ T cells into type1 (cell-mediated) and type 2 (humoral) is central for proper induction of protective immunity against pathogens. However, almost all licensed vaccines currently in use are primarily anti-body based whether intracellular or extra-cellular. In addition, converging data from both animal models and humans indicate that the production of IFN-γ alone is not sufficient to confer protection against TB. In addition, a substantial body of the literature suggests that, in addition to Th1 cells, antibody classes and sub-classes are protective against TB. In a recent study, we have shown that there is a synergy between IFN-γ (cell-mediated) and IgA (humoral) in human population in an endemic setting. In this review, current data from both animal and human studies that support mixed Th1 and Th2 responses that are protective against Mtb and other pathogens are presented.

Immunogenicity and cross-protective efficacy of double-mutant Streptococcus suis ΔSspepO/ΔSspspC serotypes 2 and 7

Streptococcus suis serotype 2 (S. suis 2) is a major pathogen causing streptococcosis in swine, resulting in significant losses in swine breeding worldwide. We previously reported that the non-antibiotic-resistant double-mutant strain ΔSspepO/ΔSspspC can be used as a live vaccine, providing effective protection against S. suis 2 infections in mice. This study aimed to understand the characteristics of streptococcosis and develop vaccine candidates for immunization. Intramuscular injection of live S. suis ΔSspepO/ΔSspspC in pigs induced discernable antibody production and provided cross-protection against challenges by a type 2 strain (100% protection) and a type 7 strain (60% protection). Protection was evaluated via clinical, bacteriological, serological, and post-mortem examinations. Furthermore, vaccination induced the production of opsonizing antibodies against serotypes 2 and 7. Analysis of IgG subclasses (IgG1 and IgG2a) revealed that both Th1 and Th2 responses were induced by S. suis ΔSspepO/ΔSspspC, although the IgG2a (Th1) response predominated over the IgG1 (Th2) response. This study is the first, to our knowledge, to establish a live vaccine candidate to protect against two major S. suis serotypes. Further studies are required to assess these candidate vaccines and examine their feasibility in providing cross-protection against S. suis.