Comparative Proteomic Analyses of Streptococcus suis Serotype 2 Cell Wall-Associated Proteins

The identification of two M20B family peptidases required for full virulence in Staphylococcus aureus

We have previously demonstrated that deletion of an intracellular leucine aminopeptidase results in attenuated virulence of S. aureus. Herein we explore the role of 10 other aminopeptidases in S. aureus pathogenesis. Using a human blood survival assay we identified mutations in two enzymes from the M20B family (PepT1 and PepT2) as having markedly decreased survival compared to the parent. We further reveal that pepT1, pepT2 and pepT1/2 mutant strains are impaired in their ability to resist phagocytosis by, and engender survival within, human macrophages. Using a co-infection model of murine sepsis, we demonstrate impairment of dissemination and survival for both single mutants that is even more pronounced in the double mutant. We show that these enzymes are localized to the cytosol and membrane but are not necessary for peptide-based nutrition, a hallmark of cell-associated aminopeptidases. Furthermore, none of the survival defects appear to be the result of altered virulence factor production. An exploration of their regulation reveals that both are controlled by known regulators of the S. aureus virulence process, including Agr, Rot and/or SarA, and that this cascade may be mediated by FarR. Structural modeling of PepT1 reveals it bears all the hallmarks of a tripeptidase, whilst PepT2 differs significantly in its catalytic pocket, suggesting a broader substrate preference. In sum, we have identified two M20B aminopeptidases that are integral to S. aureus pathogenesis. The future identification of protein and/or peptide targets for these proteases will be critical to understanding their important virulence impacting functions.

Unlocking the Secrets of Streptococcus suis: A peptidomics comparison of virulent and non-virulent serotypes 2, 14, 18, and 19

Streptococcus suis (S. suis) is an important bacterial pathogen, that causes serious infections in humans and pigs. Although numerous virulence factors have been proposed, their particular role in pathogenesis is still inconclusive. The current study explored putative peptides responsible for the virulence of S. suis serotype 2 (SS2). Thus, the peptidome of highly virulent SS2, less prevalent SS14, and rarely reported serotypes SS18 and SS19 were comparatively analyzed using a high-performance liquid chromatography-mass spectrometry method (LC-MS/MS). Six serotype-specific peptides, 2,3,4,5-tetrahydropyridine-2,6-dicarboxylate N-acetyltransferase (DapH), alanine racemase (Alr), CCA-adding enzyme (CCA), peptide chain release factor 3 (RF3), ATP synthase subunit delta (F0F1-ATPases) and aspartate carbamoyltransferase (ATCase), were expressed moderately to highly only in the SS2 peptidome with p-values of less than 0.05. Some of these proteins are responsible for bacterial cellular stability; especially, Alr was highly expressed in the SS2 peptidome and is associated with peptidoglycan biosynthesis and bacterial cell wall formation. This study indicated that these serotype-specific peptides, which were significantly expressed by virulent SS2, could serve as putative virulence factors to promote its competitiveness with other coexistences in a particular condition. Further in vivo studies of these peptides should be performed to confirm the virulence roles of these identified peptides.

Comparative immunosecretome analysis of prevalent Streptococcus suis serotypes

Streptococcus suis is a major Gram-positive swine pathogen associated with a wide variety of diseases in pigs. The efforts made to develop vaccines against this pathogen have failed because of lack of common cross-reactive antigens against different serotypes. Nowadays the interest has moved to surface and secreted proteins, as they have the highest chances to raise an effective immune response because they are in direct contact with host cells and are really exposed and accessible to antibodies. In this work, we have performed a comparative immunosecretomic approach to identify a set of immunoreactive secreted proteins common to the most prevalent serotypes of S. suis. Among the 67 proteins identified, three (SSU0020, SSU0934, and SSU0215) were those predicted extracellular proteins most widely found within the studied serotypes. These immunoreactive proteins may be interesting targets for future vaccine development as they could provide possible cross-reactivity among different serotypes of this pathogen.

Streptococcus suis vaccines: candidate antigens and progress

Streptococcus suis is a major swine pathogen and an emerging zoonotic agent of human meningitis and streptococcal toxic shock-like syndrome. S. suis is a well-encapsulated pathogen and multiple serotypes have been described based on the capsular polysaccharide antigenic diversity. In addition, high genotypic, phenotypic and geographic variability exits among strains within the same serotype. Besides, S. suis uses an arsenal of virulence factors to evade the host immune system. Together, these characteristics have challenged the development of efficacious vaccines to fight this important pathogen. In this careful and comprehensive review, clinical field information and experimental data have been compiled and compared for the first time to give a precise overview of the current status of vaccine development against S. suis. The candidate antigens and vaccine formulations under research are examined and the feasibility of reaching the goal of a "universal" cross-protective S. suis vaccine discussed.

Catabolite control protein A has an important role in the metabolic regulation of Streptococcus suis type 2 according to iTRAQ-based quantitative proteomic analysis

The catabolite control protein A (ccpA) regulates the carbon metabolism in Streptococcus suis type 2 and has pleiotropic regulatory functions in bacterial virulence and transcription. The present study systematically investigated ccpA activity in Streptococcus suis type 2 using isobaric tag for relative and absolute quantification (iTRAQ) liquid chromatography‑tandem mass spectrometry‑based proteomics. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses demonstrated that ccpA is an important protein for the regulation of metabolism, virulence and immune pathways in Streptococcus suis type 2. The present study therefore expanded the current understanding of the effects of ccpA on virulence, metabolic regulation and transcription in Streptococcus suis type 2 and other important pathogens.

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.

Candidate proteomic biomarkers for three genogroups of the swine pathogen Streptococcus suis serotype 2

BACKGROUND

Streptococcus suis, more specifically serotype 2, is a major swine pathogen and an emerging zoonotic agent that causes severe infections such as meningitis, endocarditis, and septicemia. In this study, surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI) was used to investigate the protein expression profiles of 45 strains of S. suis serotype 2 that had previously been clustered by multilocus sequence typing (MLST) into three sequence types (ST1, ST25, and ST28) (n = 15 for each ST).

RESULTS

The SELDI data were analyzed using the univariate Mann-Whitney and Kruskal-Wallis tests and multivariate statistical methods (heatmap/hierarchical clustering). The heatmap identified 136 cell proteins, and hierarchical clustering provided a 100% correct classification of all fifteen ST1 and ST25 strains and thirteen of the fifteen ST28 strains (87% correct). The univariate statistical analyses of the SELDI protein expression profiles identified nine significant proteins that discriminated the strains of the three STs of S. suis. Of these proteins, two were overexpressed in ST1 (5958 Da and 10249 Da), four in ST25 (5989 Da, 6646 Da, 7421 Da, and 9825 Da), and three in ST28 (4516 Da, 7833 Da, and 9342 Da). Two of the proteins associated with the ST28 strains (p4516 and p9342) were purified and were identified as a putative ABC transporter and a nucleoid-DNA-binding protein, respectively.

CONCLUSIONS

SELDI analysis of 45 strains of S. suis allowed to identify nine statistically significant proteins that can be specifically correlated with either ST1, ST25 or ST28. The possible involvement of the overexpressed proteins in the pathology of S. suis infections will require further investigation.

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.

Mass Spectrometric Analysis of Whole Secretome and Amylase-precipitated Secretome Proteins from Streptococcus gordonii

Oral biofilm (dental plaque) is formed by the initial adhesion of “pioneer species” to salivary proteins that form the dental pellicle on the tooth surface. One such pioneer species, Streptococcus gordonii, is known to bind salivary amylase through specific amylase-binding proteins such as amylase-binding protein A (AbpA). Recent studies have demonstrated that once bound, salivary amylase appears to modulate gene expression in S. gordonii. However, it is not known if this amylase-induced gene expression leads to secretion of proteins that play a role in plaque biofilm formation. In this study we examined the differences in secreted proteomes between S. gordonii KS1 (wild type) and AbpA-deficient (ΔAbpA) strains. We also examined the differentially precipitated secretome proteins following incubation with salivary amylase. The culture supernatants from KS1 and ΔAbpA were analyzed by nano-LC/MS/MS to characterize the whole secreted proteomes of the KS1 and ΔAbpA. A total of 107 proteins were identified in the KS1 and ΔAbpA secretomes of which 72 proteins were predicted to have an N-terminal signal peptide for secretion. Five proteins were differentially expressed between the KS1 and ΔAbpA secretomes; AbpA and sortase B were expressed exclusively by KS1, whereas Gdh, AdcA and GroEL were expressed only by ΔAbpA. Incubation of culture supernatants from KS1 and ΔAbpA with amylase (50 μg/ml) at room temperature for 2 h resulted in the differential precipitation of secretome proteins. Hypothetical protein (SGO_0483), cation-transporting ATPase YfgQ (Aha1), isocitrate dehydrogenase (Icd), sortase A (SrtA), beta-N-acetylhexosaminidase (SGO_0405), peptide chain release factor 1(PrfA) and cardiolipin synthase (SGO_2037) were precipitated by amylase from the KS1 culture supernatant. Among the identified secreted proteins and amylase-precipitated proteins, transcriptional regulator LytR (SGO_0535) and cation-transporting ATPase YfgQ (Aha1) are potential signaling proteins.

Immunoproteomics: current technology and applications

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent advances in genomics and proteomics, has led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel based, array based, mass spectrometry, DNA based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of antigens targeted by the immune system during disease.

Streptococcus suis serotype 9 bacterin immunogenicity and protective efficacy

Streptococcus suis diseases in pigs, most importantly meningitis, are worldwide responsible for major economic losses in the pig industry. About one fourth of invasive S. suis diseases are caused by S. suis serotype 9 strains in Europe. However, little is known about serotype 9 since most studies were performed with serotype 2. The objective of this study was to determine the immunogenicity and protective efficacy of a serotype 9 bacterin in piglets. Challenge was conducted with a reference serotype 9 strain, belonging to the same clonal complex but to a different sequence type as the bacterin strain. The bacterin induced protection against mortality but not morbidity. Eleven days post infection, 3 of 7 vaccinated survivors were not fully convalescent and had not eliminated the challenge strain from inner organs completely. In accordance with the clinical findings, the majority of piglets showed fibrinous-suppurative lesions in at least one inner organ or tissue. In contrast to the placebo group such lesions were not detected in one third of bacterin-vaccinated piglets. Determination of specific serum IgG titers revealed that the bacterin elicited seroconversion against muramidase-released protein and basic membrane lipoprotein. Furthermore, vaccination was associated with induction of opsonizing antibodies against the serotype 9 challenge strain. However, titers of opsonizing antibodies were rather low in comparison to those found in our previous serotype 2 vaccination trial. Piglets developed substantially higher titers of opsonizing antibodies after challenge. Opsonizing antibodies were absorbable with the serotype 9 challenge strain but not with an unencapsulated isogenic mutant of a serotype 2 strain indicating their specificity. The results indicate that a serotype 9 bacterin is less protective than a serotype 2 bacterin, most likely due to inducing only low titers of opsonizing antibodies. This might contribute to emergence of serotype 9 strains, in particular strains of this clonal complex, in Europe.

Immunoproteomic analysis of the antibody response obtained in Nile tilapia following vaccination with a Streptococcus iniae vaccine

Streptococcus iniae is one of the most economically important Gram-positive pathogens in cultured fish species worldwide. The USDA-ARS Aquatic Animal Health Research Unit developed a modified (contains concentrated culture supernatant) S. iniae bacterin that has been demonstrated to be efficacious, and protection is mediated by specific anti-S. iniae antibodies. Although effective, the specific vaccine components important for efficacy are not known. In the present study, an immunoproteomic approach was utilized to identify whole-cell lysate proteins of S. iniae that stimulated specific antibody production in Nile tilapia (Oreochromis niloticus) following vaccination. Groups of tilapia were vaccinated by intraperitoneal injection with the modified S. iniae bacterin or were mock-vaccinated, and at 30 d post-vaccination sera samples were obtained from individual fish. Vaccination of tilapia with the S. iniae vaccine stimulated significantly elevated specific antibody responses against proteins of the bacterium and passive immunization of tilapia with this serum demonstrated the antibodies were highly protective. Whole-cell lysate proteins of S. iniae were separated by 2D-PAGE and were probed with a pooled serum sample from vaccinated tilapia. A total of eleven unique immunogenic proteins were positively identified by mass spectrometry. Based on research conducted on homologous proteins in other Streptococcus spp., antibodies specific for three of the identified proteins, enolase, glyceraldehyde-3-phosphate dehydrogenase, and fructose-bisphosphate aldolase, are likely involved in protection from streptococcosis caused by S. iniae.