Catabolite control protein A of Streptococcus suis type 2 contributes to sugar metabolism and virulence

Ultrasound-assisted extraction of emodin from Rheum officinale Baill and its antibacterial mechanism against Streptococcus suis based on CcpA

Emodin was extracted from Rheum officinale Baill by ultrasound-assisted extraction (UAE), and ethanol was chosen as the suitable solvent through SEM and molecular dynamic simulation. Under the optimum conditions (power 541 W, time 23 min, liquid to material ratio 13:1 mL/g, ethanol concentration 83 %) predicted by RSM, the yield of emodin was 2.18 ± 0.11 mg/g. Moreover, ultrasound power and time displayed the significant effects on the extraction process. Extracting dynamics analysis indicated that the extraction process of emodin by UAE conformed to Fick's second diffusion law. The results of antibacterial experiments suggested that emodin can damage cell membrane and inhibit the expression of cps2A, sao, mrp, epf, neu and the hemolytic activity of S. suis. Biolayer interferometry and FT-IR multi-peak fitting assays demonstrated that emodin induced a secondary conformational shift in CcpA. Molecular docking and molecular dynamics confirmed that emodin bound to CcpA through hydrogen bonding (ALA248, GLU249, GLY129 and ASN196) and π-π T-shaped interaction (TYR225 and TYR130), and the mutation of amino acid residues affected the affinity of CcpA to emodin. Therefore, emodin inhibited the sugar utilization of S. suis through binding to CcpA, and CcpA may be a potential target to inhibit the growth of S. suis.

Thioredoxin A of Streptococcus suis Serotype 2 Contributes to Virulence by Inhibiting the Expression of Pentraxin 3 to Promote Survival Within Macrophages

Streptococcus suis serotype 2 (SS2) is an important zoonotic pathogen that can infect humans in contact with infected pigs or their byproducts. It can employ different types of genes to defend against oxidative stress and ensure its survival. The thioredoxin (Trx) system is a key antioxidant system that contributes adversity adaptation and pathogenicity. SS2 has been shown to encode putative thioredoxin genes, but the biological roles, coding sequence, and underlying mechanisms remains uncharacterized. Here, we demonstrated that SSU05_0237-ORF, from a clinical SS2 strain, ZJ081101, encodes a protein of 104 amino acids with a canonical CGPC active motif and an identity 70-85% similar to the thioredoxin A (TrxA) in other microorganisms. Recombinant TrxA efficiently catalyzed the thiol-disulfide oxidoreduction of insulin. The deletion of TrxA led to a significantly slow growth and markedly compromised tolerance of the pathogen to temperature stress, as well as impaired adhesion ability to pig intestinal epithelial cells (IPEC-J2). However, it was not involved in H2O2 and paraquat-induced oxidative stress. Compared with the wild-type strain, the ΔTrxA strain was more susceptible to killing by macrophages through increasing NO production. Treatment with TrxA mutant strain also significantly attenuated cytotoxic effects on RAW 264.7 cells by inhibiting inflammatory response and apoptosis. Knockdown of pentraxin 3 in RAW 264.7 cells was more vulnerable to phagocytic activity, and TrxA promoted SS2 survival in phagocytic cells depending on pentraxin 3 activity compared with the wild-type strain. Moreover, a co-inoculation experiment in mice revealed that TrxA mutant strain is far more easily cleared from the body than the wild type strain in the period from 8-24 h, and exhibits significantly attenuated oxidative stress and liver injury. In summary, we reveal the important role of TrxA in the pathogenesis of SS2.

Role of Metabolic Adaptation of Streptococcus suis to Host Niches in Bacterial Fitness and Virulence

Streptococcus suis, both a common colonizer of the porcine upper respiratory tract and an invasive pig pathogen, successfully adapts to different host environments encountered during infection. Whereas the initial infection mainly occurs via the respiratory tract, in a second step, the pathogen can breach the epithelial barrier and disseminate within the whole body. Thereby, the pathogen reaches other organs such as the heart, the joints, or the brain. In this review, we focus on the role of S. suis metabolism for adaptation to these different in vivo host niches to encounter changes in nutrient availability, host defense mechanisms and competing microbiota. Furthermore, we highlight the close link between S. suis metabolism and virulence. Mutants deficient in metabolic regulators often show an attenuation in infection experiments possibly due to downregulation of virulence factors, reduced resistance to nutritive or oxidative stress and to phagocytic activity. Finally, metabolic pathways as potential targets for new therapeutic strategies are discussed. As antimicrobial resistance in S. suis isolates has increased over the last years, the development of new antibiotics is of utmost importance to successfully fight infections in the future.

The biological role of MutT in the pathogenesis of the zoonotic pathogen Streptococcus suis serotype 2

Streptococcus suis (S. suis) is an important rising pathogen that causes serious diseases in humans and pigs. Although some putative virulence factors of S. suis have been identified, its pathogenic mechanisms are largely unclear. Here, we identified a putative virulence-associated factor MutT, which is unique to S. suis serotype 2 (SS2) virulent strains. To investigate the biological roles of MutT in the SS2 virulent strain ZY05719, the mutT knockout mutant (ΔmutT) was generated and used to explore the phenotypic and virulent variations between the parental and ΔmutT strains. We found that the mutT mutation significantly inhibited cell growth ability, shortened the chain length, and displayed a high susceptibility to H2O2-induced oxidative stress. Moreover, this study revealed that MutT induced the adhesion and invasion of SS2 to host cells. Deletion of mutT increased microbial clearance in host tissues of the infected mice. Sequence alignment results suggested that mutT was encoded in a strain-specific manner, in which the detection was strongly linked to bacterial pathogenicity. In both zebrafish and mice infection models, the virulence of ΔmutT was largely reduced compared with that of ZY05719. Overall, this study provides compelling evidence that MutT is indispensable for the virulence of SS2 and highlights the biological role of MutT in bacteria pathogenesis during infection.

Identification of conditionally essential genes for Streptococcus suis infection in pigs

Streptococcus suis

is a Gram-positive bacterium and zoonotic pathogen that causes meningitis and sepsis in pigs and humans. The aim of this study was to identify genes required for S. suis infection. We created Tn-Seq libraries in a virulent S. suis strain 10, which was used to inoculate pigs in an intrathecal experimental infection. Comparative analysis of the relative abundance of mutants recovered from different sites of infection (blood, cerebrospinal fluid, and meninges of the brain) identified 361 conditionally essential genes, i.e. required for infection, which is about 18% of the genome. The conditionally essential genes were primarily involved in metabolic and transport processes, regulation, ribosomal structure and biogenesis, transcription, and cell wall membrane and envelope biogenesis, stress defenses, and immune evasion. Directed mutants were created in a set of 10 genes of different genetic ontologies and their role was determined in ex vivo models. Mutants showed different levels of sensitivity to survival in whole blood, serum, cerebrospinal fluid, thermic shock, and stress conditions, as compared to the wild type. Additionally, the role of three selected mutants was validated in co-infection experiments in which pigs were infected with both wild type and isogenic mutant strains. The genetic determinants of infection identified in this work contribute to novel insights in S. suis pathogenesis and could serve as targets for novel vaccines or antimicrobial drugs.

ICESsuHN105, a Novel Multiple Antibiotic Resistant ICE in Streptococcus suis Serotype 5 Strain HN105

Streptococcussuis serotype 5, an emerging zoonosis bacterial pathogen, has been isolated from infections in both pigs and humans. In this study, we sequenced the first complete genome of a virulent, multidrug-resistant SS5 strain HN105. The strain HN105 displayed enhanced pathogenicity in zebrafish and BABL/c mouse infection models. Comparative genome analysis identified a novel 80K integrative conjugative element (ICE), ICESsuHN105, as required for the multidrug resistance phenotype. Six corresponding antibiotic resistance genes in this ICE were identified, namely tet (O), tet (M), erm (two copies), aph, and spc. Phylogenetic analysis classified the element as a homolog of the ICESa2603 family, containing the typical family backbone and insertion DNA. DNA hybrids mediated by natural transformation between HN105 and ZY05719 verified the antibiotic resistant genes of ICESsuHN105 that could be transferred successfully, while they were dispersedly inserted with a single gene in different genomic locations of ZY05719_(HN105) transformants. To further identify the horizontal transfer of ICESsuHN105 as a whole mobile genetic element, a circular intermediate form of ICESsuHN105 was detected by PCR. However, the effective conjugation using serotype 2 S. suis as recipients was not observed in current assays in vitro. Further studies confirmed the presence of the complete lantibiotic locus encoded in ICESsuHN105 that effectively inhibits the growth of other streptococci. In summary, this study demonstrated the presence of antibiotic resistance genes in ICE that are able to transfer between different clinical isolates and adapt to a broader range of Streptococcus serotype or species.

Enhanced Production of Polymyxin E in Paenibacillus polymyxa by Replacement of Glucose by Starch

Polymyxin E or colistin, produced by Paenibacillus polymyxa, is an important antibiotic against Gram-negative pathogens. The objective of this study is to evaluate the effect of starch in fermentation medium on colistin biosynthesis in P. polymyxa. The results indicated that replacement of glucose by starch stimulated colistin production and biosynthesis rate. Overall, the stimulation extent was starch concentration-dependent. As expected, addition of starch induced the expression of amyE encoding amylase and increased amylase activity in fermentation solution. Additionally, replacement of glucose by starch resulted in residue reducing sugar and pH of fermentation mixture low relative to glucose as the sole sugar source. At the molecular level, it was found that replacement of glucose by starch has enhanced the relative expression level of ccpA encoding catabolite control protein A. Therefore, the repression of starch utilization by glucose could be probably relieved. In addition, use of starch stimulated the expression of regulatory gene spo0A but repressed the expression of another regulatory gene abrB. As a result, the expression of genes directly involved in colistin biosynthesis and secretion increased, indicating that at the transcriptional level spo0A and abrB played opposite roles in regulating colistin biosynthesis in P. polymyxa. Taken together, our data demonstrated that starch instead of glucose can promote colistin production probably by affecting the expression of colistin biosynthesis-related genes, as well as reducing the repression of glucose to a secondary metabolic product.

The VraSR regulatory system contributes to virulence in Streptococcus suis via resistance to innate immune defenses

Streptococcus suis is a highly invasive pathogen that can cause sepsis and meningitis in pigs and humans. However, we have limited understanding of the mechanisms S. suis uses to evade innate immunity. To investigate the involvement of the two-component signal transduction system of S. suis in host immune defense, we examined the expression of 15 response regulators of S. suis following stimulation with polymorphonuclear leukocytes (PMNs). We found that several response regulators were significantly up-regulated including vraR. Thus, we constructed an isogenic deletion mutant of vraSR genes in S. suis and demonstrated VraSR promotes both bacterial survival in human blood and resistance to human PMN-mediated killing. The VraSR mutant was more susceptible to phagocytosis by human PMNs and had greater sensitivity to oxidant and lysozyme than wild-type S. suis. Furthermore, in vitro findings and in vivo evidence from a mouse infection model together strongly demonstrate that ΔvraSR had greatly attenuated virulence compared with wild-type S. suis. Collectively, our data reveal that VraSR is a critical regulatory system that contributes to the survival of S. suis and its ability to defend against host innate immunity.

Role of two-component regulatory systems in the virulence of Streptococcus suis

Streptococcus suis is an important zoonotic pathogen that causes severe infections and great economic losses worldwide. Understanding how this pathogen senses and responds to environmental signals during the infectious process can offer insight into its pathogenesis and may be helpful in the development of drug targets. Two-component regulatory systems (TCSs) play an essential role in this environmental response. In S. suis, at least 15 groups of TCSs have been predicted. Among them, several have been demonstrated to be involved in virulence and/or stress response. In this review, we discuss the progress in the study of TCSs in S. suis, focusing on the role of these systems in the virulence of this bacterium.

Regulation of the β-hemolysin gene cluster of Streptococcus anginosus by CcpA

Streptococcus anginosus is increasingly recognized as an opportunistic pathogen. However, our knowledge about virulence determinants in this species is scarce. One exception is the streptolysin-S (SLS) homologue responsible for the β-hemolytic phenotype of the S. anginosus type strain. In S. anginosus the expression of the hemolysin is reduced in the presence of high glucose concentrations. To investigate the genetic mechanism of the hemolysin repression we created an isogenic ccpA deletion strain. In contrast to the wild type strain, this mutant exhibits hemolytic activity in presence of up to 25 mM glucose supplementation, a phenotype that could be reverted by ccpA complementation. To further demonstrate that CcpA directly regulates the hemolysin expression, we performed an in silico analysis of the promoter of the SLS gene cluster and we verified the binding of CcpA to the promoter by electrophoretic mobility shift assays. This allowed us to define the CcpA binding site in the SLS promoter region of S. anginosus. In conclusion, we report for the first time the characterization of a potential virulence regulator in S. anginosus.

Streptococcus suis DivIVA Protein Is a Substrate of Ser/Thr Kinase STK and Involved in Cell Division Regulation

Streptococcus suis serotype 2 is an important swine pathogen and an emerging zoonotic agent that causes severe infections. Recent studies have reported a eukaryotic-like Ser/Thr protein kinase (STK) gene and characterized its role in the growth and virulence of different S. suis 2 strains. In the present study, phosphoproteomic analysis was adopted to identify substrates of the STK protein. Seven proteins that were annotated to participate in different cell processes were identified as potential substrates, which suggests the pleiotropic effects of stk on S. suis 2 by targeting multiple pathways. Among them, a protein characterized as cell division initiation protein (DivIVA) was further investigated. In vitro analysis demonstrated that the recombinant STK protein directly phosphorylates threonine at amino acid position 199 (Thr-199) of DivIVA. This effect could be completely abolished by the T199A mutation. To determine the specific role of DivIVA in growth and division, a divIVA mutant was constructed. The ΔdivIVA strain exhibited impaired growth and division, including lower viability, enlarged cell mass, asymmetrical division caused by aberrant septum, and extremely weak pathogenicity in a mouse infection model. Collectively, our results reveal that STK regulates the cell growth and virulence of S. suis 2 by targeting substrates that are involved in different biological pathways. The inactivation of DivIVA leads to severe defects in cell division and strongly attenuates pathogenicity, thereby indicating its potential as a molecular drug target against S. suis.

Streptococcus suis small RNA rss04 contributes to the induction of meningitis by regulating capsule synthesis and by inducing biofilm formation in a mouse infection model

Streptococcus suis (SS) is an important pathogen for pigs, and it is also considered as a zoonotic agent for humans. Meningitis is one of the most common features of the infection caused by SS, but little is known about the mechanisms of SS meningitis. Recent studies have revealed that small RNAs (sRNAs) have emerged as key regulators of the virulence in several bacteria. In the previous study, we reported that SS sRNA rss04 was up-regulated in pig cerebrospinal fluid and contributes to SS virulence in a zebrafish infection model. Here, we show that rss04 facilitates SS invasion of mouse brain and lung in vivo. Label-free quantitation mass spectrometry analysis revealed that rss04 regulates transcriptional regulator CcpA and several virulence factors including LuxS. Transmission electron microscope and Dot-blot analyses indicated that rss04 represses capsular polysaccharide (CPS) production, which in turn facilitates SS adherence and invasion of mouse brain microvascular endothelial cells bEnd.3 in vitro and activates the mRNA expression of TLR2, CCL2, IL-6 and TNF-α in mouse brain in vivo at 12h post-infection. In addition, rss04 positively regulates SS biofilm formation. Survival analysis of infected mice showed that biofilm state in brain contributes to SS virulence by intracranial subarachnoidal route of infection. Together, our data reveal that SS sRNA rss04 contributes to the induction of meningitis by regulating the CPS synthesis and by inducing biofilm formation, thereby increasing the virulence in a mouse infection model. To our knowledge, rss04 represents the first bacterial sRNA that plays definitive roles in bacterial meningitis.

Stress Physiology of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance.

Investigation into the role of catabolite control protein A in the metabolic regulation of Streptococcus suis serotype 2 using gene expression profile analysis

Catabolite control protein A (CcpA) serves a key function in the catabolism of Streptococcus suis serotype 2 (S. suis 2) by affecting the biological function and metabolic regulatory mechanisms of this bacterium. The aim of the present study was to identify variations in CcpA expression in S. suis 2 using gene expression profile analysis. Using sequencing and functional analysis, CcpA was demonstrated to play a regulatory role in the expression and regulation of virulence genes, carbon metabolism and immunoregulation in S. suis 2. Gene Ontology and Kyto Encyclopedia of Genes and Genomes analyses indicated that CcpA in S. suis 2 is involved in the regulation of multiple metabolic processes. Furthermore, combined analysis of the transcriptome and metabolite data suggested that metabolites varied due to the modulation of gene expression levels under the influence of CcpA regulation. In addition, metabolic network analysis indicated that CcpA impacted carbon metabolism to a certain extent. Therefore, the present study has provided a more comprehensive analysis of the role of CcpA in the metabolic regulation of S. suis 2, which may facilitate future investigation into this mechanism. Furthermore, the results of the present study provide a foundation for further research into the regulatory function of CcpA and associated metabolic pathways in S. suis 2.

Superoxide dismutase of Streptococcus suis serotype 2 plays a role in anti-autophagic response by scavenging reactive oxygen species in infected macrophages

Streptococcus suis serotype 2 (SS2) causes septic shock and meningitis. However, its pathogenesis is still not well-understood. We have recently shown that superoxide dismutase sodA of SS2 is a virulence factor probably by increasing resistance to oxidative stresses. Reactive oxygen species (ROS) are products of the respiratory burst of phagocytic cells and have been shown to activate autophagy. We wanted to know if and how SS2 explores its sodA to interfere with cell autophagic responses. A sodA deletion mutant (Δsod) was compared with its parent and complemented strain in autophagic response in the murine macrophage cell line RAW264.7. We found that the Δsod mutant induced significant autophagic responses in infected cells, shown as increased LC3 lipidation (LC3-II) and EGFP-LC3 punctae, than those infected by its parent or complemented strain at 1 or 2h post-infection. Co-localization of the autophagosomal EGFP-LC3 vesicles with lysosomes was seen in cells infected with Δsod mutant and its parent strain, indicating that SS2 infection induced complete autophagic responses. Reduced autophagic responses of cells infected with the wild-type strain might be related to decreased ROS by the scavenging effect of its sodA, as shown by increased superoxide anion or ROS level in cells infected with the Δsod mutant and in the cell free xanthine oxidase-hypoxanthine ROS-generating system, as compared with its parent or complemented strain. Taken together, SS2 makes use of its sodA for survival not only by scavenging ROS but also by alleviating the host autophagic responses due to ROS stimulation.

Two Spx regulators modulate stress tolerance and virulence in Streptococcus suis serotype 2

Streptococcus suis serotype 2 is an important zoonotic pathogen causing severe infections in pigs and humans. The pathogenesis of S. suis 2 infections, however, is still poorly understood. Spx proteins are a group of global regulators involved in stress tolerance and virulence. In this study, we characterized two orthologs of the Spx regulator, SpxA1 and SpxA2 in S. suis 2. Two mutant strains (ΔspxA1 and ΔspxA2) lacking the spx genes were constructed. The ΔspxA1 and ΔspxA2 mutants displayed different phenotypes. ΔspxA1 exhibited impaired growth in the presence of hydrogen peroxide, while ΔspxA2 exhibited impaired growth in the presence of SDS and NaCl. Both mutants were defective in medium lacking newborn bovine serum. Using a murine infection model, we demonstrated that the abilities of the mutant strains to colonize the tissues were significantly reduced compared to that of the wild-type strain. The mutant strains also showed a decreased level of survival in pig blood. Microarray analysis revealed a global regulatory role for SpxA1 and SpxA2. Furthermore, we demonstrated for the first time that Spx is involved in triggering the host inflammatory response. Collectively, our data suggest that SpxA1 and SpxA2 are global regulators that are implicated in stress tolerance and virulence in S. suis 2.

Catabolite control protein A is an important regulator of metabolism in Streptococcus suis type 2

Streptococcus suis (S. suis) type 2 is an extremely important Gram-positive bacterial pathogen that can cause human or swine endocarditis, meningitis, bronchopneumonia, arthritis and sepsis. Catabolite control protein A (CcpA) is a major transcriptional regulator in S. suis type 2 that functions in catabolite control, specifically during growth on glucose or galactose. The regulation of central metabolism can affect the virulence of bacteria. In the present study, a metabolomics approach was used along with principal components analysis (PCA) and partial least-squares-discriminant analysis (PLS-DA) models and 37 metabolites were found that differed substantially between native S. suis and a mutant lacking CcpA. These results showed that CcpA is an important protein in S. suis type 2 for studying bacterial protein function.

CcpA is important for growth and virulence of Enterococcus faecium

The collagen adhesin Acm was the first virulence determinant reported to be important for the pathogenesis of Enterococcus faecium in a rat infective endocarditis model. We had previously reported that there was a slight growth delay associated with acm allelic replacement (cat) mutant strain TX6051 used in that study. Recently, we generated a nonpolar markerless acm deletion mutant and did not observe a delay in growth. We therefore performed comparative genome sequence analysis of wild-type strain TX82 and TX6051 and found a single mutation, a nonsense mutation in the ccpA gene of TX6051. After correcting this mutation, the growth defect of TX6051 was abolished, implicating a role for CcpA in the growth of E. faecium. To confirm this, we created a ccpA deletion mutant of TX82, which also exhibited a slight delay in growth. Furthermore, the ccpA deletion mutant was attenuated (P = 0.0024) in a mixed-inoculum (TX82 plus TX82 ΔccpA) rat endocarditis model and also in an in vitro competitive growth assay; a ccpA-complemented strain showed neither reduced growth nor reduced virulence. We also found attenuation in the endocarditis model with the new acm deletion mutant although not as great as that previously observed with TX6051 carrying the ccpA mutation. Taken together, our data confirm the role of Acm in the pathogenesis of endocarditis. We also show that CcpA affects the growth of E. faecium, that an intact ccpA gene is important for full virulence, and that a ccpA mutation was partly responsible for the highly attenuated phenotype of TX6051.

RNA-seq analysis of the influence of anaerobiosis and FNR on Shigella flexneri

Background

Shigella flexneri is an important human pathogen that has to adapt to the anaerobic environment in the gastrointestinal tract to cause dysentery. To define the influence of anaerobiosis on the virulence of Shigella, we performed deep RNA sequencing to identify transcriptomic differences that are induced by anaerobiosis and modulated by the anaerobic Fumarate and Nitrate Reduction regulator, FNR.

Results

We found that 528 chromosomal genes were differentially expressed in response to anaerobic conditions; of these, 228 genes were also influenced by FNR. Genes that were up-regulated in anaerobic conditions are involved in carbon transport and metabolism (e.g. ptsG, manX, murQ, cysP, cra), DNA topology and regulation (e.g. ygiP, stpA, hns), host interactions (e.g. yciD, nmpC, slyB, gapA, shf, msbB) and survival within the gastrointestinal tract (e.g. shiA, ospI, adiY, cysP). Interestingly, there was a marked effect of available oxygen on genes involved in Type III secretion system (T3SS), which is required for host cell invasion and pathogenesis. These genes, located on the large Shigella virulence plasmid, were down regulated in anaerobiosis in an FNR-dependent manner. We also confirmed anaerobic induction of csrB and csrC small RNAs in an FNR-independent manner.

Conclusions

Anaerobiosis promotes survival and adaption strategies of Shigella, while modulating virulence plasmid genes involved in T3SS-mediated host cell invasion. The influence of FNR on this process is more extensive than previously appreciated, although aside from the virulence plasmid, this transcriptional regulator does not govern expression of genes on other horizontally acquired sequences on the chromosome such as pathogenicity islands.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-438) contains supplementary material, which is available to authorized users.

Streptococcus suis type 2 SSU0587 protein is a beta-galactosidase that contributes to bacterial adhesion but not to virulence in mice

Bacterial surface proteins play key roles in virulence and often contribute to bacterial adhesion and invasion. We discovered that the Streptococcus suis type 2 (SS2) gene SSU0587 encodes a protein of 1,491 amino acids that possesses β-galactosidase activity. The surface association of the protein was dependent upon sortase activity. Deleting SSU0587 from clinical SS2 isolate JX081101 caused a loss of both β-galactosidase activity and adherence to microvascular endothelial cells. Deleting SSU0587 had no measurable impact on either invasion of microvascular endothelial cells or on virulence in a murine infection model, although the concentration of JX081101ΔSSU0587 was reduced in the brains of infected mice, as compared with the pathogen loads of the wild-type strain.

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

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