Studies of fibronectin-binding proteins of Streptococcus equi

Bacterial and host factors involved in zoonotic Streptococcal meningitis

Zoonotic streptococci cause several invasive diseases with high mortality rates, especially meningitis. Numerous studies elucidated the meningitis pathogenesis of zoonotic streptococci, some specific to certain bacterial species. In contrast, others are shared among different bacterial species, involving colonization and invasion of mucosal barriers, survival in the bloodstream, breaching the blood-brain and/or blood-cerebrospinal fluid barrier to access the central nervous system, and triggering inflammation of the meninges. This review focuses on the recent advancements in comprehending the molecular and cellular events of five major zoonotic streptococci responsible for causing meningitis in humans or animals, including Streptococcus agalactiae, Streptococcus equi subspecies zooepidemicus, Streptococcus suis, Streptococcus dysgalactiae, and Streptococcus iniae. The underlying mechanism was summarized into four themes, including 1) bacterial survival in blood, 2) brain microvascular endothelial cell adhesion and invasion, 3) penetration of the blood-brain barrier, and 4) activation of the immune system and inflammatory reaction within the brain. This review may contribute to developing therapeutics to prevent or mitigate injury of streptococcal meningitis and improve risk stratification.

Comparative Genomic Analysis of Streptococcus dysgalactiae subspecies dysgalactiae Isolated From Bovine Mastitis in China

Streptococcus dysgalactiae subsp. dysgalactiae (SDSD) is one of the most prevalent pathogens causing bovine mastitis worldwide. However, there is a lack of comprehensive information regarding genetic diversity, complete profiles of virulence factors (VFs), and antimicrobial resistance (AMR) genes for SDSD associated with bovine mastitis in China. In this study, a total of 674 milk samples, including samples from 509 clinical and 165 subclinical mastitis cases, were collected from 17 herds in 7 provinces in China from November 2016 to June 2019. All SDSD isolates were included in phylogenetic analysis based on 16S rRNA and multi-locus sequence typing (MLST). In addition, whole genome sequencing was performed on 12 representative SDSD isolates to screen for VFs and AMR genes and to define pan-, core and accessory genomes. The prevalence of SDSD from mastitis milk samples was 7.57% (51/674). According to phylogenetic analysis based on 16S rRNA, 51 SDSD isolates were divided into 4 clusters, whereas based on MLST, 51 SDSD isolates were identified as 11 sequence types, including 6 registered STs and 5 novel STs (ST521, ST523, ST526, ST527, ST529) that belonged to 2 distinct clonal complexes (CCs) and 4 singletons. Based on WGS information, 108 VFs genes in 12 isolates were determined in 11 categories. In addition, 23 AMR genes were identified in 11 categories. Pan-, core and accessory genomes were composed of 2,663, 1,633 and 699 genes, respectively. These results provided a comprehensive profiles of SDSD virulence and resistance genes as well as phylogenetic relationships among mastitis associated SDSD in North China.

Identification of genes required for the fitness of Streptococcus equi subsp. equi in whole equine blood and hydrogen peroxide

The availability of next-generation sequencing techniques provides an unprecedented opportunity for the assignment of gene function. Streptococcus equi subspecies equi is the causative agent of strangles in horses, one of the most prevalent and important diseases of equids worldwide. However, the live attenuated vaccines that are utilized to control this disease cause adverse reactions in some animals. Here, we employ transposon-directed insertion-site sequencing (TraDIS) to identify genes that are required for the fitness of S. equi in whole equine blood or in the presence of H2O2 to model selective pressures exerted by the equine immune response during infection. We report the fitness values of 1503 and 1471 genes, representing 94.5 and 92.5 % of non-essential genes in S. equi, following incubation in whole blood and in the presence of H2O2, respectively. Of these genes, 36 and 15 were identified as being important to the fitness of S. equi in whole blood or H2O2, respectively, with 14 genes being important in both conditions. Allelic replacement mutants were generated to validate the fitness results. Our data identify genes that are important for S. equi to resist aspects of the immune response in vitro, which can be exploited for the development of safer live attenuated vaccines to prevent strangles.

Pathogenicity Factors in Group C and G Streptococci

Initially recognized zoonoses, streptococci belonging to Lancefield group C (GCS) and G (GGS) were subsequently recognised as human pathogens causing a diverse range of symptoms, from asymptomatic carriage to life threatening diseases. Their taxonomy has changed during the last decade. Asymptomatic carriage is <4% amongst the human population and invasive infections are often in association with chronic diseases such as diabetes, cardiovascular diseases or chronic skin infections. Other clinical manifestations include acute pharyngitis, pneumonia, endocarditis, bacteraemia and toxic-shock syndrome. Post streptococcal sequalae such as rheumatic fever and acute glomerulonephritis have also been described but mainly in developed countries and amongst specific populations. Putative virulence determinants for these organisms include adhesins, toxins, and other factors that are essential for dissemination in human tissues and for interference with the host immune responses. High nucleotide similarities among virulence genes and their association with mobile genetic elements supports the hypothesis of extensive horizontal gene transfer events between the various pyogenic streptococcal species belonging to Lancefield groups A, C and G. A better understanding of the mechanisms of pathogenesis should be apparent by whole-genome sequencing, and this would result in more effective clinical strategies for the pyogenic group in general.

Genetics and Pathogenicity Factors of Group C and G Streptococci

Of the eight phylogenetic groups comprising the genus Streptococcus, Lancefield group C and G streptococci (GCS and GGS, resp.) occupy four of them, including the Pyogenic, Anginosus, and Mitis groups, and one Unnamed group so far. These organisms thrive as opportunistic commensals in both humans and animals but may also be associated with clinically serious infections, often resembling those due to their closest genetic relatives, the group A streptoccci (GAS). Advances in molecular genetics, taxonomic approaches and phylogenomic studies have led to the establishment of at least 12 species, several of which being subdivided into subspecies. This review summarizes these advances, citing 264 early and recent references. It focuses on the molecular structure and genetic regulation of clinically important proteins associated with the cell wall, cytoplasmic membrane and extracellular environment. The article also addresses the question of how, based on the current knowledge, basic research and translational medicine might proceed to further advance our understanding of these multifaceted organisms. Particular emphasis in this respect is placed on streptokinase as the protein determining the host specificity of infection and the Rsh-mediated stringent response with its potential for supporting bacterial survival under nutritional stress conditions.

Identification and characterization of a novel protective antigen, Sec_205 of Streptococcus equi ssp. Zooepidemicus

Streptococcus equi ssp. zooepidemicus (SEZ) is an important pathogen of swine streptococcal diseases and can infect a wide range of animals as well as human beings. The absence of effective vaccine confounds the control of SEZ infection. Sec_205, a novel protein identified in the previous study, was inducibly over-expressed in Escherichia coli in the present study. The purified recombinant protein could elicit a significant humoral antibody response and provide efficient protection against lethal challenge of SEZ C55138 in mouse model. The protection against SEZ infection was mediated by specific antibodies to Sec_205 to some extent and was identified by the passive protection assay. The Sec_205 was an in vivo-induced antigen confirmed by the real-time PCR and could adhere to the Hep-2 cells by the inhibition assay. These suggest that Sec_205 may play a vital role in pathogenicity and serve as a new vaccine candidate against SEZ infection.

Collagen-like proteins of pathogenic streptococci

The collagen domain, which is defined by the presence of the Gly-X-Y triplet repeats, is amongst the most versatile and widespread known structures found in proteins from organisms representing all three domains of life. The streptococcal collagen-like (Scl) proteins are widely present in pathogenic streptococci, including Streptococcus pyogenes, S. agalactiae, S. pneumoniae, and S. equi. Experiments and bioinformatic analyses support the hypothesis that all Scl proteins are homotrimeric and cell wall-anchored. These proteins contain the rod-shaped collagenous domain proximal to cell surface, as well as a variety of outermost non-collagenous domains that generally lack predicted functions but can be grouped into one of six clusters based on sequence similarity. The well-characterized Scl1 proteins of S. pyogenes show a dichotomous switch in ligand binding between human tissue and blood environments. In tissue, Scl1 adhesin specifically recognizes the wound microenvironment, promotes adhesion and biofilm formation, decreases bacterial killing by neutrophil extracellular traps, and modulates S. pyogenes virulence. In blood, ligands include components of complement and coagulation-fibrinolytic systems, as well as plasma lipoproteins. In all, the Scl proteins signify a large family of structurally related surface proteins, which contribute to the ability of streptococci to colonize and cause diseases in humans and animals.

Identification of novel genes expressed during host infection in Streptococcus equi ssp. zooepidemicus ATCC35246

Infection with Streptococcus equi ssp. zooepidemicus (Streptococcus zooepidemicus, SEZ) can cause septicemia, meningitis, and mastitis in domesticated species. Identification of this organism's virulence factors is an effective way of clarifying its pathogenic mechanism. We employed in vivo-induced antigen technology (IVIAT) to find bacterial genes that were only expressed or upregulated in an infected host (IVI genes). Convalescent-phase sera from pigs infected with SEZ were pooled, adsorbed against in vitro antigens, and used to screen SEZ genomic expression libraries. This analysis identified 43 genes as IVI genes. Six of these 43 genes were verified via real-time PCR. Following the analysis, we were able to assign a putative function to 36 of the 43 proteins. These proteins included those involved in virulence and adaptation; formation of intermediary products; gene replication, transcription and expression; energy metabolism; transport and also various proteins of unknown function. The relationship between sagD gene and bacterial virulence was confirmed. This study provides new molecular data for the study of streptococcal disease in swine and is important for identifying the pathogenic mechanisms of SEZ.

Bivalent ligation of the collagen-binding modules of fibronectin by SFS, a non-anchored bacterial protein of Streptococcus equi

SFS is a non-anchored protein of Streptococcus equi subspecies equi that causes upper respiratory infection in horses. SFS has been shown to bind to fibronectin (FN) and block interaction of FN with type I collagen. We have characterized interactions of a recombinant 60-mer polypeptide, R1R2, with FN. R1R2 contains two copies of collagen-like 19-residue repeats. Experiments utilizing various FN fragments and epitope-mapped anti-FN monoclonal antibodies located the binding site to (8-9)FNI modules of the gelatin-binding domain. Fluorescence polarization and competitive enzyme-linked assays demonstrated that R1R2 binds preferentially to compact dimeric FN rather than monomeric constructs containing (8-9)FNI or a large dimeric FN construct that is constitutively in an extended conformation. In contrast to bacterial peptides that bind (2-5)FNI in addition to (8-9)FNI, R1R2 did not cause conformational extension of FN as assessed by a conformationally sensitive antibody. Equilibrium and stopped-flow binding assays and size exclusion chromatography were compatible with a two-step binding reaction in which each of the repeats of R1R2 interacts with one of the subunits of dimeric FN, resulting in a stable complex with a slow koff. In addition to not binding to type I collagen, the R1R2·FN complex incorporated less efficiently into extracellular matrix than free FN. Thus, R1R2 binds to FN utilizing features of compact soluble FN and in doing so interferes with the organization of the extracellular matrix. A similar bivalent binding strategy may underlie the collagen-FN interaction.

Structural and functional analysis of the fibronectin-binding protein FNE from Streptococcus equi spp. equi

Streptococcus equi is a horse pathogen belonging to Lancefield group C. Infection by S. equi ssp. equi causes strangles, a serious and highly contagious disease of the upper respiratory tract. S. equi ssp. equi secretes a fibronectin (Fn)-binding protein, FNE, that does not contain cell wall-anchoring motifs. FNE binds to the gelatin-binding domain (GBD) of Fn, composed of the motifs (6) FI (12) FII (789) FI . FNE lacks the canonical Fn-binding peptide repeats observed in many microbial surface components recognizing adhesive matrix molecules. We found that the interaction between FNE and the human GBD is mediated by the binding of the disordered C-terminal region (residues 208-262) of FNE to the (789) FI GBD subfragment. The crystal structure of FNE showed that it is similar to the minor pilus protein Spy0125 of Streptococcus pyogenes, found at the end of pilus polymers and responsible for adhesion. FNE and Spy0125 both have a superimposable internal thioester bond between highly conserved Cys and Gln residues. Small-angle X-ray scattering of the FNE-(789) FI complex provided a model that aligns the C-terminal peptide of FNE with the E-strands of the FI domains, adopting the β-zipper extension model observed in previous structures of microbial surface components recognizing adhesive matrix molecule adhesion peptides bound to FI domains.

Propolis modulates fibronectin expression in the matrix of thermal injury

The aim of the study was to assess the propolis effect on fibronectin metabolism in the course of burn wounds healing process. A model of burn wound healing of pig skin was applied. The amount of the released glycoprotein was assessed by a surface plasmon resonance. The profile of extracted fibronectin components was also assessed by an electrophoresis in polyacrylamide gel, with a subsequent immunodetection by Western Blotting. Propolis burn treatment decreased the release of fibronectin components from healing wounds in relation to damages treated with silver sulfadiazine. The main reason of decreased extraction of fibronectin components from wounds treated with propolis was a substantial decrease of degradation product release of the mentioned glycoprotein, which was observed particularly from the 3rd to 5th day of the repair. Wounds treatment with propolis demonstrated, especially in relation to damages treated with silver sulfadiazine, the decreased release of synthesized fibronectin molecules. The obtained results suggest that propolis modifies fibronectin metabolism in the course of wound healing process. The influence of propolis is reflected in prevention of fibronectin biosynthesis as well as its degradation in the wound area. The above-mentioned metabolic changes may decrease the risk of complications in the repair wounds process.

Insight into the specific virulence related genes and toxin-antitoxin virulent pathogenicity islands in swine streptococcosis pathogen Streptococcus equi ssp. zooepidemicus strain ATCC35246

Background

Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is an important pathogen causing swine streptococcosis in China. Pathogenicity islands (PAIs) of S. zooepidemicus have been transferred among bacteria through horizontal gene transfer (HGT) and play important roles in the adaptation and increased virulence of S. zooepidemicus. The present study used comparative genomics to examine the different pathogenicities of S. zooepidemicus.

Results

Genome of S. zooepidemicus ATCC35246 (Sz35246) comprises 2,167,264-bp of a single circular chromosome, with a GC content of 41.65%. Comparative genome analysis of Sz35246, S. zooepidemicus MGCS10565 (Sz10565), Streptococcus equi. ssp. equi. 4047 (Se4047) and S. zooepidemicus H70 (Sz70) identified 320 Sz35246-specific genes, clustered into three toxin-antitoxin (TA) systems PAIs and one restriction modification system (RM system) PAI. These four acquired PAIs encode proteins that may contribute to the overall pathogenic capacity and fitness of this bacterium to adapt to different hosts. Analysis of the in vivo and in vitro transcriptomes of this bacterium revealed differentially expressed PAI genes and non-PAI genes, suggesting that Sz35246 possess mechanisms for infecting animals and adapting to a wide range of host environments. Analysis of the genome identified potential Sz35246 virulence genes. Genes of the Fim III operon were presumed to be involved in breaking the host-restriction of Sz35246.

Conclusion

Genome wide comparisons of Sz35246 with three other strains and transcriptome analysis revealed novel genes related to bacterial virulence and breaking the host-restriction. Four specific PAIs, which were judged to have been transferred into Sz35246 genome through HGT, were identified for the first time. Further analysis of the TA and RM systems in the PAIs will improve our understanding of the pathogenicity of this bacterium and could lead to the development of diagnostics and vaccines.

Proteome variation among Filifactor alocis strains

Filifactor alocis, a Gram-positive anaerobic rod, is now considered one of the marker organisms associated with periodontal disease. Although there was heterogeneity in its virulence potential, this bacterium was shown to have virulence properties that may enhance its ability to survive and persist in the periodontal pocket. To gain further insight into a possible mechanism(s) of pathogenesis, the proteome of F. alocis strains was evaluated. Proteins including several proteases, neutrophil-activating protein A and calcium-binding acid repeat protein, were identified in F. alocis. During the invasion of HeLa cells, there was increased expression of several of the genes encoding these proteins in the potentially more virulent F. alocis D-62D compared to F. alocis ATCC 35896, the type strain. A comparative protein in silico analysis of the proteome revealed more cell wall anchoring proteins in the F. alocis D-62D compared to F. alocis ATCC 35896. Their expression was enhanced by coinfection with Porphyromonas gingivalis. Taken together, the variation in the pathogenic potential of the F. alocis strains may be related to the differential expression of several putative virulence factors.

Contribution of fibronectin-binding protein to pathogenesis of Streptococcus equi ssp. zooepidemicus

Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is responsible for a wide variety of infections in many species. Fibronectin-binding protein is a bacterial cell surface protein, which specifically binds fibronectin (FN). Considering the specific role of FN-binding protein in host-pathogen interactions, we investigated the function of a novel FN-binding domain in the FN-binding protein (FNZ) of S. zooepidemicus. Five recombinant FNZ gene fragments [N1 (amino acids, 38-197), N2 (amino acids, 38-603), N3 (amino acids, 41-315), N4 (amino acids, 192-370), and N5 (amino acids, 38-225)] were expressed in Escherichia coli, and their FN-binding activities were tested. The results showed that amino acids 192-225 in the NH2 -terminal region of FNZ could be responsible for binding fibronectin. The FNZ knockout mutant was constructed in S. zooepidemicus, which results in the reduced capacity to adhere to HEp-2 cell, defective virulence in vivo, decreased biofilm formation, and decreased colonization capacity in blood, liver, lung, and spleen tissues of mice as compared to the wild type. These results suggest that FNZ participates in biofilm formation, FN binding, cell adhesion, and pathogenesis of S. zooepidemicus. Furthermore, this work offers a novel FN-binding domain within FNZ, which will help in further characterization of S. zooepidemicus FN-binding properties.

Manuka honey inhibits the development of Streptococcus pyogenes biofilms and causes reduced expression of two fibronectin binding proteins

Streptococcus pyogenes (group A Streptococcus; GAS) is always of clinical significance in wounds where it can initiate infection, destroy skin grafts and persist as a biofilm. Manuka honey has broad spectrum antimicrobial activity and its use in the clinical setting is beginning to gain acceptance with the continuing emergence of antibiotic resistance and the inadequacy of established systemic therapies; novel inhibitors may affect clinical practice. In this study, the effect of manuka honey on S. pyogenes (M28) was investigated in vitro with planktonic and biofilm cultures using MIC, MBC, microscopy and aggregation efficiency. Bactericidal effects were found in both planktonic cultures and biofilms, although higher concentrations of manuka honey were needed to inhibit biofilms. Abrogation of adherence and intercellular aggregation was observed. Manuka honey permeated 24 h established biofilms of S. pyogenes, resulting in significant cell death and dissociation of cells from the biofilm. Sublethal concentrations of manuka honey effectively prevented the binding of S. pyogenes to the human tissue protein fibronectin, but did not inhibit binding to fibrinogen. The observed inhibition of fibronectin binding was confirmed by a reduction in the expression of genes encoding two major fibronectin-binding streptococcal surface proteins, Sof and SfbI. These findings indicate that manuka honey has potential in the topical treatment of wounds containing S. pyogenes.

Getting to grips with strangles: an effective multi-component recombinant vaccine for the protection of horses from Streptococcus equi infection

Streptococcus equi subspecies equi (S. equi) is a clonal, equine host-adapted pathogen of global importance that causes a suppurative lymphodendopathy of the head and neck, more commonly known as Strangles. The disease is highly prevalent, can be severe and is highly contagious. Antibiotic treatment is usually ineffective. Live attenuated vaccine strains of S. equi have shown adverse reactions and they suffer from a short duration of immunity. Thus, a safe and effective vaccine against S. equi is highly desirable. The bacterium shows only limited genetic diversity and an effective vaccine could confer broad protection to horses throughout the world. Welsh mountain ponies (n = 7) vaccinated with a combination of seven recombinant S. equi proteins were significantly protected from experimental infection by S. equi, resembling the spontaneous disease. Vaccinated horses had significantly reduced incidence of lymph node swelling (p = 0.0013) lymph node abscessation (p = 0.00001), fewer days of pyrexia (p = 0.0001), reduced pathology scoring (p = 0.005) and lower bacterial recovery from lymph nodes (p = 0.004) when compared with non-vaccinated horses (n = 7). Six of 7 vaccinated horses were protected whereas all 7 non-vaccinated became infected. The protective antigens consisted of five surface localized proteins and two IgG endopeptidases. A second vaccination trial (n = 7+7), in which the IgG endopeptidases were omitted, demonstrated only partial protection against S. equi, highlighting an important role for these vaccine components in establishing a protective immune response. S. equi shares >80% sequence identity with Streptococcus pyogenes. Several of the components utilized here have counterparts in S. pyogenes, suggesting that our findings have broader implications for the prevention of infection with this important human pathogen. This is one of only a few demonstrations of protection from streptococcal infection conferred by a recombinant multi-component subunit vaccine in a natural host.

Numerous research groups have vaccinated, using recombinant antigens, against streptococcal infections in mouse model systems and shown protection. We have here demonstrated efficient protective vaccination of the natural host, the horse, using recombinant antigens. Streptococcus equi subspecies equi (S. equi) is an equine host-adapted and highly contagious pathogen of global importance. Six out of seven Welsh mountain ponies vaccinated with a combination of seven recombinant S. equi proteins were protected from experimental infection as assessed by clinical examination, pyrexia, lymph node swelling, inflammation, bacterial recovery, and post mortem examination. The protective antigens consisted of five surface localized proteins and two endopeptidases that are specific for IgG; the latter were shown to be of major importance for efficacy. Several of the antigens used here have similarities in Streptococcus pyogenes, implying that our findings are of importance for development of a vaccine against this important human pathogen.

Vaccination of horses against strangles using recombinant antigens from Streptococcus equi

Strangles is an upper respiratory tract infection in horses, which is highly contagious and one of the more costly diseases of the horse. Three recombinant antigens were used to vaccinate horses, which were then experimentally challenged with Streptococcus equi, the causative agent for strangles. The vaccinated horses showed significantly reduced bacterial growth (p=0.02) and nasal discharge (p=0.0004), a typical symptom of strangles. Other clinical signs of strangles were also reduced and at post mortem examination, lower rate of empyaema or scarring of the guttural pouches was found in the vaccinated group (p=0.01). The antigens used were EAG (alpha2-macroglobulin, albumin, and IgG-binding protein), CNE (a collagen-binding protein), and SclC (a collagen-like protein). The adjuvant used was Abisco, a saponin derived matrix. No adverse effects were observed following vaccination with the antigens and adjuvant.

A fibronectin-binding protein from Streptococcus equi binds collagen and modulates cell-mediated collagen gel contraction

The N-terminal fragment (FNZN) of the fibronectin-binding protein FNZ from Streptococcus equi subspecies zooepidemicus was investigated as to effects on murine cell interactions with extracellular matrix proteins. FNZN bound to immobilized fibronectin (FN) and native, but not denatured, collagen type I. FNZN had no effect on primary adhesion of cells from the murine myoblastic C2C12 cell line to immobilized fibronectin. C2C12 cells adhered to immobilized FNZN, a process that was not inhibited by anti-human FN IgG or by an inhibitor of integrin alphaVbeta3. C2C12 cells lack collagen-binding beta1 integrins and neither adhere to native collagen nor mediate contraction of three-dimensional collagen gels. FNZN stimulated collagen gel contraction by C2C12 cells but not adhesion of C2C12 cells to collagen. Experiments with an alphaVbeta3-inhibitor suggested that FNZN promoted contraction by a process requiring alphaVbeta3. Our data suggest that FNZN by binding to cells, collagen, and FN modulate complex adhesive processes mediated by the alphaVbeta3 integrin. Since alphaVbeta3-mediated contractile events function to counteract edema formation during inflammation, it is possible that FNZN and its secreted homologue FNE modulate edema responses in infected tissues.