Identification of group B streptococcal Sip protein, which elicits cross-protective immunity

Protease SfpB plays an important role in cell membrane stability and immune system evasion in Streptococcus agalactiae

Bacteria possess the ability to develop diverse and ingenious strategies to outwit the host immune system, and proteases are one of the many weapons employed by bacteria. This study sought to identify S. agalactiae additional serine protease and determine its role in virulence. The S. agalactiae THN0901 genome features one S8 family serine peptidase B (SfpB), acting as a secreted and externally exposed entity. A S8 family serine peptidase mutant strain (ΔsfpB) and complement strain (CΔsfpB) were generated through homologous recombination. Compared to the wild-type strain THN0901, the absorption of EtBr dyes was significantly reduced (P < 0.01) in ΔsfpB, implying an altered cell membrane permeability. In addition, the ΔsfpB strain had a significantly lower survival rate in macrophages (P < 0.01) and a 61.85 % lower adhesion ability to the EPC cells (P < 0.01) compared to THN0901. In the in vivo colonization experiment using tilapia as a model, 210 fish were selected and injected with different bacterial strains at a concentration of 3 × 106 CFU/tail. At 6, 12, 24, 48, 72 and 96 h post-injection, three fish were randomly selected from each group and their brain, liver, spleen, and kidney tissues were isolated. Subsequently, it was demonstrated that the ΔsfpB strain exhibited a markedly diminished capacity for colonization in tilapia. Additionally, the cumulative mortality of ΔsfpB in fish after intraperitoneal injection was reduced by 19.92-23.85 %. In conclusion, the findings in this study have demonstrated that the SfpB plays a significant role in S. agalactiae cell membrane stability and immune evasion. The immune evasion is fundamental for the development and transmission of invasive diseases, the serine protease SfpB may be a promising candidate for the development of antimicrobial agents to reduce the transmission of S. agalactiae.

A nanocarrier immersion vaccine encoding surface immunogenic protein confers cross-immunoprotection against Streptococcus agalactiae and Streptococcus iniae infection in tilapia

Streptococcosis is a highly contagious aquatic bacterial disease that poses a significant threat to tilapia. Vaccination is a well-known effective measure to prevent and control fish bacterial diseases. Among the various immunization methods, immersion vaccination is simple and can be widely used in aquaculture. Besides, nanocarrier delivery technology has been reported as an effective solution to improve the immune effect of immersion vaccine. In this study, the surface immunogenic protein (Sip) was proved to be conserved and potential to provide cross-immunoprotection for both Streptococcus agalactiae (S. agalactiae) and Streptococcus iniae (S. iniae) by multiple sequences alignment and Western blotting analysis. On this basis, we expressed and obtained the recombinant protein rSip and connected it with functionalized carbon nanotubes (CNT) to construct the nanocarrier vaccine system CNT-rSip. After immersion immunization, the immune effect of CNT-rSip against above two streptococcus infections was evaluated in tilapia based on some aspects including the serum specific antibody level, non-specific enzyme activities, immune-related genes expression and relative percent survival (RPS) after bacteria challenge. The results showed that compared with control group, CNT-rSip significantly (P < 0.05) increased the serum antibody levels, related enzyme activities including acid phosphatase, alkaline phosphatase, lysozyme and total antioxidant capacity activities, as well as the expression levels of immune-related genes from 2 to 4 weeks post immunization (wpi), and all these indexes peaked at 3 wpi. Besides, the above indexes of CNT-rSip were higher than those of rSip group with different extend during the experiment. Furthermore, the challenge test indicated that CNT-rSip provided cross-immunoprotection against S. agalactiae and S. iniae infection with RPS of 75 % and 72.41 %, respectively, which were much higher than those of other groups. Our study indicated that the nanocarrier immersion vaccine CNT-rSip could significantly improve the antibody titer and confer cross-immuneprotection against S. agalactiae and S. iniae infection in tilapia.

Exploring the Immunoprotective Potential of a Nanocarrier Immersion Vaccine Encoding Sip against Streptococcus Infection in Tilapia (Oreochromis niloticus)

Tilapia, as one of the fish widely cultured around the world, is suffering severe impact from the streptococcus disease with the deterioration of the breeding environment and the increasing of breeding density, which brings serious economic loss to tilapia farming. In this study, the surface immunogenic protein (Sip) of Streptococcus agalactiae (S. agalactiae) was selected as the potential candidate antigen and connected with bacterial nano cellulose (BNC) to construct the nanocarrier subunit vaccine (BNC-rSip), and the immersion immune effects against S. agalactiae and Streptococcus iniae (S. iniae) in Nile tilapia were evaluated on the basis of the serum antibody level, non-specific enzyme activity, the immune-related gene expression and relative percent survival (RPS). The results indicated that Sip possessed the expected immunogenicity according to the immunoinformatic analysis. Compared with the rSip group, BNC-rSip significantly induced serum antibody production and improved the innate immunity level of tilapia. After challenge, the RPS of BNC-rSip groups were 78.95% (S. agalactiae) and 67.86% (S. iniae), which were both higher than those of rSip groups,31.58% (S. agalactiae) and 35.71% (S. iniae), respectively. Our study indicated that BNC-rSip can induce protective immunity for tilapia through immersion immunization and may be an ideal candidate vaccine for controlling tilapia streptococcal disease.

Ultra-Fast Impedimetric Immunoassay for Detection of Streptococcus agalactiae Using Carbon Electrode with Nanodiamonds Film

This publication presents the results of work on the development of a quick and cheap electrochemical immunosensor for the diagnosis of infections with the pathogen Streptococcus agalactiae. The research was carried out on the basis of the modification of the well-known glassy carbon (GC) electrodes. The surface of the GC (glassy carbon) electrode was covered with a film made of nanodiamonds, which increased the number of sites for the attachment of anti-Streptococcus agalactiae antibodies. The GC surface was activated with EDC/NHS (1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-Hydroxysuccinimide). Determination of electrode characteristics after each modification step, performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).

Characterization and virulence of Streptococcus agalactiae deficient in SaeRS of the two-component system

There are a variety of regulatory systems in bacteria, among which the two-component system (TCS) can sense external environmental changes and make a series of physiological and biochemical reactions, which is crucial for the life activities of bacteria. As a member of TCS, SaeRS is considered to be an important virulence factor in Staphylococcus aureus, but its function in tilapia (Oreochromis niloticus)-derived Streptococcus agalactiae remains unknown. To explore the role of SaeRS in regulating virulence in the two-component system (TCS) of S. agalactiae from tilapia, ΔSaeRS mutant strain and CΔSaeRS complementary strain were constructed by homologous recombination. The results showed that the abilities of growth and biofilm formation of ΔSaeRS strain were significantly decreased when cultured in a brain heart infusion (BHI) medium (P < 0.01). Also, the survival rate of the ΔSaeRS strain in blood was decreased when compared with the wild strain S. agalactiae THN0901. Under the higher infection dose, the accumulative mortality of tilapia caused by the ΔSaeRS strain was significantly decreased (23.3%), of which THN0901 and CΔSaeRS strains were 73.3%. The results of competition experiments in tilapia showed that the invasion and colonization abilities of the ΔSaeRS strain were also dramatically lower than those of the wild strain (P < 0.01). Compared with the THN0901, the mRNA expression levels of virulence factors (fbsB, sip, cylE, bca, etc.) in the ΔSaeRS strain were significantly down-regulated (P < 0.01). SaeRS is one of the virulence factors of S. agalactiae. It plays a role in promoting host colonization and achieving immune evasion during the infection of tilapia, which provides a basis for exploring the pathogenic mechanism of S. agalactiae infected with tilapia.

Designing multi-epitope-based vaccine targeting surface immunogenic protein of Streptococcus agalactiae using immunoinformatics to control mastitis in dairy cattle

Background

Milk provides energy as well as the basic nutrients required by the body. In particular, milk is beneficial for bone growth and development in children. Based on scientific evidence, cattle milk is an excellent and highly nutritious dietary component that is abundant in vitamins, calcium, potassium, and protein, among other minerals. However, the commercial productivity of cattle milk is markedly affected by mastitis. Mastitis is an economically important disease that is characterized by inflammation of the mammary gland. This disease is frequently caused by microorganisms and is detected as abnormalities in the udder and milk. Streptococcus agalactiae is a prominent cause of mastitis. Antibiotics are rarely used to treat this infection, and other available treatments take a long time to exhibit a therapeutic effect. Vaccination is recommended to protect cattle from mastitis. Accordingly, the present study sought to design a multi-epitope vaccine using immunoinformatics.

Results

The vaccine was designed to be antigenic, immunogenic, non-toxic, and non-allergic, and had a binding affinity with Toll-like receptor 2 (TLR2) and TLR4 based on structural modeling, docking, and molecular dynamics simulation studies. Besides, the designed vaccine was successfully expressed in E. coli. expression vector (pET28a) depicts its easy purification for production on a larger scale, which was determined through in silico cloning. Further, immune simulation analysis revealed the effectiveness of the vaccine with an increase in the population of B and T cells in response to vaccination.

Conclusion

This multi-epitope vaccine is expected to be effective at generating an immune response, thereby paving the way for further experimental studies to combat mastitis.

Protein-Based Adjuvants for Vaccines as Immunomodulators of the Innate and Adaptive Immune Response: Current Knowledge, Challenges, and Future Opportunities

New-generation vaccines, formulated with subunits or nucleic acids, are less immunogenic than classical vaccines formulated with live-attenuated or inactivated pathogens. This difference has led to an intensified search for additional potent vaccine adjuvants that meet safety and efficacy criteria and confer long-term protection. This review provides an overview of protein-based adjuvants (PBAs) obtained from different organisms, including bacteria, mollusks, plants, and humans. Notably, despite structural differences, all PBAs show significant immunostimulatory properties, eliciting B-cell- and T-cell-mediated immune responses to administered antigens, providing advantages over many currently adopted adjuvant approaches. Furthermore, PBAs are natural biocompatible and biodegradable substances that induce minimal reactogenicity and toxicity and interact with innate immune receptors, enhancing their endocytosis and modulating subsequent adaptive immune responses. We propose that PBAs can contribute to the development of vaccines against complex pathogens, including intracellular pathogens such as Mycobacterium tuberculosis, those with complex life cycles such as Plasmodium falciparum, those that induce host immune dysfunction such as HIV, those that target immunocompromised individuals such as fungi, those with a latent disease phase such as Herpes, those that are antigenically variable such as SARS-CoV-2 and those that undergo continuous evolution, to reduce the likelihood of outbreaks.

Virulence Factor Genes and Cytotoxicity of Streptococcus agalactiae Isolated from Bovine Mastitis in Poland

Streptococcus agalactiae can produce a wide variety of virulence factors, including toxins and proteins which facilitate adhesion to and colonization and invasion of the host cells. There are few reports on the characteristics of field isolates from bovine mastitis in Poland. Thus, the aim of this study was to determine the occurrence of types of hemolysis on blood agar, virulence factor genes, and cytotoxicity of S. agalactiae isolates derived from cows with mastitis across Poland. The study included 68 isolates. Virulence genes were tested using standard PCR, and cytotoxicity was determined using methylthiazol tetrazolium (MTT) and lactate dehydrogenase (LDH) tests. Among the tested isolates, 89.7% were β-hemolytic, 8.8% γ-hemolytic, and 1.5% alpha-hemolytic. The only genes detected in all isolates were the cfb, cspA, hylB, and sip genes. Cytotoxicity assessment based on the LDH test revealed that isolates were cytotoxic only to Vero cells. However, according to the results obtained from the MTT test, more than half of the isolates exhibited low cytotoxicity to both SK and Vero cells, whereas the other isolates showed moderate or no cytotoxicity to both cell lines. Our research confirms the prevalence of various virulence genes in S. agalactiae isolated from Polish dairy herds, which have previously been found in isolates recovered from human and animal infections. For the first time, the presence of bac- and scpB-positive isolates of S. agalactiae was determined in Polish dairy cattle, and the cytotoxicity of bovine isolates was assessed. IMPORTANCE We believe that this manuscript is one of the few reports on the characteristics of field S. agalactiae isolates derived from cases of bovine mastitis in cows in Poland in terms of the occurrence of virulence genes and cytotoxicity. For the first time, the presence of bac- and scpB-positive isolates of S. agalactiae was determined in Polish dairy cattle, and the cytotoxicity of bovine isolates was assessed.

Streptococcal bacterial components in cancer therapy

The incidence rate of cancer is steadily increasing all around the world, and there is an urgent need to develop novel and more effective treatment strategies. Recently, bacterial therapy has been investigated as a new approach to target cancer, and is becoming a serious option. Streptococcus strains are among the most common and well-studied virulent bacteria that cause a variety of human infections. Everyone has experienced a sore throat during their lifetime, or has been asymptomatically colonized by streptococci. The ability of Streptococcus bacteria to fight cancer was discovered more than 100 years ago, and over the years has undergone clinical trials, but the mechanism is not yet completely understood. Recently, several animal models and human clinical trials have been reported. Streptococcal strains can have an intrinsic anti-tumor activity, or can activate the host immune system to fight the tumor. Bacteria can selectively accumulate and proliferate in the hypoxic regions of solid tumors. Moreover, the bacteria can be genetically engineered to secrete toxins or enzymes that can specifically attack the tumors.

Immunogenic Proteins of Group B Streptococcus-Potential Antigens in Immunodiagnostic Assay for GBS Detection

Streptococcus agalactiae (Group B Streptococcus, GBS) is an opportunistic pathogen, which asymptomatically colonizes the gastrointestinal and genitourinary tract of up to one third of healthy adults. Nevertheless, GBS carriage in pregnant women may lead to several health issues in newborns causing life threatening infection, such as sepsis, pneumonia or meningitis. Recommended GBS screening in pregnant women significantly reduced morbidity and mortality in infants. Nevertheless, intrapartum antibiotic prophylaxis, recommended following the detection of carriage or in case of lack of a carriage test result for pregnant women who demonstrate certain risk factors, led to the expansion of the adverse phenomenon of bacterial resistance to antibiotics. In our paper, we reviewed some immunogenic GBS proteins, i.e., Alp family proteins, β protein, Lmb, Sip, BibA, FsbA, ScpB, enolase, elongation factor Tu, IMPDH, and GroEL, which possess features characteristic of good candidates for immunodiagnostic assays for GBS carriage detection, such as immunoreactivity and specificity. We assume that they can be used as an alternative diagnostic method to the presently recommended bacteriological cultivation and MALDI.

Clinical utilization of species-specific immunoassays for identification of Staphylococcus aureus and Streptococcus agalactiae in orthopedic infections

Staphylococcus aureus and Streptococcus agalactiae (Group B streptococcus, GBS) are common causes of deep musculoskeletal infections (MSKI) and result in significant patient morbidity and cost to the healthcare system. One of the major challenges with MSKI is the lack of faithful diagnostics to correctly identify the primary pathogen, as standard culture-based assays are prone to false positives in the case of polymicrobial infections, and false negatives due to limitations in sample acquisition and antibiotic use before presentation. To improve upon our current diagnostic methods for MSKI, we developed a multiplex immunoassay for antigen-specific IgGs in serum (Luminex), and medium enriched for newly synthesized antibodies (MENSA) for anti-S. aureus and GBS generated from cultured peripheral blood mononuclear cells (PBMCs) of orthopedic infection patients undergoing surgical treatment. Samples were obtained from 110 MSKI patients: 80 diabetic foot ulcer, 21 periprosthetic joint infection, 5 septic arthritis, 2 spine, 1 hand, and 1 fracture-related infection (FRI). Anti-S. aureus and anti-GBS antibody titers were compared to culture results to assess their concordance in identifying the pathogens. Immunoassay, particularly MENSA, showed high diagnostic potential for monomicrobial S. aureus and GBS orthopedic infections (AUC > 0.95). MENSA also demonstrated diagnostic potential for GBS polymicrobial orthopedic infection and for GBS DFU (AUC > 0.83 for both). Serum showed high diagnostic potential for S. aureus PJI (AUC > 0.95). Taken together, these findings support the development of species-specific immunoassays for the identification of causal pathogens in active MSKI, especially in conjunction with standard culture.

The Recombinant Expression Proteins FnBP and ClfA From Staphylococcus aureus in Addition to GapC and Sip From Streptococcus agalactiae Can Protect BALB/c Mice From Bacterial Infection

Dairy cow mastitis is a serious disease that is mainly caused by intramammary infection with Staphylococcus aureus and Streptococcus agalactiae [group B streptococcus (GBS)]. FnBP and ClfA are the virulence factors of S. aureus, while GapC is the respective factor for S. agalactiae. Sip is a highly immunogenic protein, and it is conserved in all GBS serotypes. In this study, we analyzed the abovementioned four genes prepared a FnBP+ClfA chimeric protein (FC), a GapC+Sip chimeric protein (GS), and a FnBP+ClfA+GapC+Sip chimeric protein (FCGS) based on the antigenic sites to evaluate their use in vaccine development. After expression and purification of the recombinant proteins in Escherichia coli, BALB/c mice were immunized with them to examine resistance effects. The total lethal and half lethal doses of S. aureus and S. agalactiae were then measured, and the immunoprotective effects of the fusion proteins were evaluated. The FC and FCGS chimeric proteins could induce mice to produce high levels of antibodies, and bacterial loads were significantly reduced in the spleens and livers after challenge. After immunization with FCGS, the recipients resisted the attacks of both S. aureus and S. agalactiae, indicating the potential of the fusion protein as a mastitis vaccine.

Phenotype, genotype and pathogenicity of Streptococcus agalactiae isolated from cultured tilapia (Oreochromis spp.) in Taiwan

Tilapia (Oreochromis spp.) is globally used as an aquaculture fish species due to its high growth rate and disease resistance. However, it faces an increased risk of streptococcosis. Streptococcus agalactiae, also known as group B streptococcus (GBS), is the most important tilapia pathogen in Asia. Studies of Str. agalactiae infection in Taiwan are still unclear. Thus, this study aimed to explore the phenotype, genotype and pathogenicity of Str. agalactiae isolated from cultured tilapia in Taiwan in 2016-2018. The analysis revealed that 85% of the strains displayed β-haemolysis and 15% showed γ-haemolysis, with the same capsule level, and were positive for the CAMP test. The Rapid ID 32 Strep test showed a similarity of Rapid ID 32 Strep is more than 99.5% to GBS. Genotypic distribution by molecular serotyping detected only serotype Ia from all isolates, despite the regional differences. Pulsed-field gel electrophoresis (PFGE) was categorized into 3 and 10 clusters by restriction enzymes SmaI and ApaI, respectively. Virulence genes and antimicrobial resistance genes presented the same profile in all isolates. The challenge test with 10⁶  CFU/fish (LD₅₀ ), administered intraperitoneally, showed that the β-haemolysis strains had a higher mortality rate than γ-haemolysis, although they were from the same cluster from PFGE, year and region.

Computational design of a new multi-epitope vaccine using immunoinformatics approach against mastitis disease

Mastitis disease causes significant economic losses in dairy farms by reducing milk production, increasing production costs, and reducing milk quality. Streptococcus agalactiae continues to be a major cause of mastitis in dairy cattle. To date, there has been no approved multi-epitope vaccine against this pathogen in the market. In the present study, an efficient multi-epitope vaccine against S. agalactiae, the causative agent of mastitis, was designed using various immonoinformtics approaches. Potential epitopes were selected from Sip protein to improve vaccine immunogenicity. The designed vaccine is more antigenic in nature. Then, linkers and profilin adjuvant were added to enhance the immunity of vaccines. The designed vaccine was evaluated in terms of molecular weight, PI, immunogenicity, Toxicity, and allergenicity. Prediction of three-dimensional (3 D) structure of multi-epitope vaccine, followed by refinement and validation, was conducted to obtain a high-quality 3 D structure of the designed multi-epitope vaccine. The designed vaccine was then subjected to molecular docking with Toll-like receptor 11 (TLR11) receptor to evaluate its binding efficiency followed by dynamic simulation for stable interaction. In silico cloning approach was carried out to improve the expression of the vaccine construct. These analyses indicate that the designed multi-epitope vaccine may produce particular immune responses against S. agalactiae and may be further helpful to control mastitis after in vitro and in vivo immunological assays.

Bacterial protein domains with a novel Ig-like fold target human CEACAM receptors

Streptococcus agalactiae, also known as group B Streptococcus (GBS), is the major cause of neonatal sepsis in humans. A critical step to infection is adhesion of bacteria to epithelial surfaces. GBS adhesins have been identified to bind extracellular matrix components and cellular receptors. However, several putative adhesins have no host binding partner characterised. We report here that surface‐expressed β protein of GBS binds to human CEACAM1 and CEACAM5 receptors. A crystal structure of the complex showed that an IgSF domain in β represents a novel Ig‐fold subtype called IgI3, in which unique features allow binding to CEACAM1. Bioinformatic assessment revealed that this newly identified IgI3 fold is not exclusively present in GBS but is predicted to be present in adhesins from other clinically important human pathogens. In agreement with this prediction, we found that CEACAM1 binds to an IgI3 domain found in an adhesin from a different streptococcal species. Overall, our results indicate that the IgI3 fold could provide a broadly applied mechanism for bacteria to target CEACAMs.

Multidrug-Resistant Streptococcus agalactiae Strains Found in Human and Fish with High Penicillin and Cefotaxime Non-Susceptibilities

Penicillin non-susceptible Streptococcus agalactiae (PEN-NS GBS) has been increasingly reported, with multidrug-resistant (MDR) GBS documented in Japan. Here we identified two PEN-NS GBS strains during our surveillance studies: one from a patient's wound and the other from a tilapia. The patient's GBS (H21) and fish GBS (F49) were serotyped and tested for antibiotic susceptibility. Whole-genome sequencing was performed to find the sequence type, antimicrobial resistance genes, and mutations in penicillin-binding proteins (PBPs) and fluoroquinolone (FQ) resistance genes. H21 and F49 belonged to ST651, serotype Ib, and ST7, serotype Ia, respectively. H21 showed PEN and cefotaxime minimum inhibitory concentrations (MICs) of 2.0 mg/L. F49 showed PEN MIC 0.5 mg/L. H21 was MDR with ermB, lnuB, tetS, ant6-Ia, sat4a, and aph3-III antimicrobial resistance genes observed. Alignment of PBPs showed the combination of PBP1B (A95D) and 2B mutations (V80A, S147A, S160A) in H21 and a novel mutation in F49 at N192S in PBP2B. Alignment of FQ-resistant determinants revealed mutation sites on gyrA, gyrB, and parC and E in H21. To our knowledge, this is the first report of GBS isolates with such high penicillin and cefotaxime MICs. This raises the concern of emergence of MDR and PEN-NS GBS in and beyond healthcare facilities.

Immunization with a recombinant BibA surface protein confers immunity and protects mice against group B Streptococcus (GBS) vaginal colonization

Streptococcus agalactiae or group B Streptococcus (GBS) is a Gram-positive bacterium divided into ten distinct serotypes that colonizes the vaginal and rectal tracts of approximately 30% of women worldwide. GBS is the leading cause of invasive infection in newborns, causing sepsis, pneumoniae and meningitis. The main strategy to prevent GSB infection in newborns includes the use of intrapartum antibiotic therapy, which does not prevent late-onset diseases and may select resistant bacterial strains. We still do not have a vaccine formulation specific for this pathogen approved for human use. Conserved surface proteins are potential antigens that could be targets for recognition by antibodies and activation of cell opsonization. We used a serotype V GBS (GBS-V)-derived recombinant surface protein, rBibA, and evaluated the potential protective role of the induced antigen-specific antibodies after parenteral or mucosal immunizations in C57BL/6 mice. In vitro and in vivo assays demonstrated that vaccine formulations containing BibA combined with different adjuvants induced serum IgG and/or secreted IgA antibodies, leading to enhanced opsonophagocytosis of GBS-V cells and reduced invasion of epithelial cells. One BibA-based vaccine formulation adjuvanted with a nontoxic derivative of the heat-labile toxin produced by enterotoxigenic Escherichia coli (ETEC) strains was capable of inducing protection against vaginal colonization and lethal parenteral challenge with GBS-V. Serum collected from vaccinated mice conferred passive protection against vaginal colonization in naïve mice challenged with GBS-V. Taken together, the present data demonstrate that the BibA protein is a promising antigen for development of a vaccine to protect against GBS infection.

Development and analytical validation of real-time PCR for the detection of Streptococcus agalactiae in pregnant women

Background

Group B Streptococcus (GBS) is the leading cause of invasive neonatal infection. In this study, we aimed to evaluate the analytical validation of qualitative real-time polymerase chain reaction (qPCR) as a means to detect GBS.

Methods

Genomic DNA (gDNA) was purified from 12 ATCC bacterial strains, two belonging to GBS and the remainder acting as negative controls. Additionally, gDNA was isolated from 21 strains of GBS from various serotypes (Ia, Ib and II-VIII). All gDNA was used to evaluate the analytical validation of the qPCR method employing a specific Taqman probe. Inclusivity, exclusivity, anticipated reportable range, the limit of detection and robustness were evaluated. The methods used are described in international guidelines and other existing reports. The performance of this qPCR method for detecting GBS was compared to other microbiological methods used with vaginal-rectal samples from pregnant women.

Results

Our qPCR method for detecting GBS was analytically validated. It has a limit of detection of 0.7 GE/μL and 100% analytical specificity. It detects all strains of GBS with the same level of performance as microbiological methods.

Conclusion

Data suggest that this qPCR method performs adequately as a means to detect GBS in vaginal-rectal swabs from pregnant women.

Quantitative detection of streptococcosis infection in dead samples of Nile Tilapia (Oreochromis niloticus)

AIMS

The aims of the study were to evaluate whether epidemic strains of streptococcosis infected tilapia can be isolated and identified from dead fish for epidemiological investigation.

METHODS AND RESULTS

Firstly, tilapias were inoculated with a lethal dose (1 × 10⁸  CFU per fish) of Streptococcus agalactiae and brain tissues were harvested for bacteriological examination and qPCR assay 3, 12, 24 and 48 h postdeath. Streptococcus agalactiae was the only dominant bacterium cultivated on the brain heart infusion (BHI) plate and the bacterial load was about 10⁷  CFU per mg. Secondly, tilapia were killed via ice water shock and immersed either in an aquarium containing 2·27 × 10⁴  CFU per ml S. agalactiae or in a pond with streptococcosis outbreak. Streptococcus agalactiae failed to grow on the BHI plate but were identified (<6 × 10²  CFU per mg) via qPCR assay. Finally, an epidemiological investigation of streptococcosis was conducted in the main tilapia breeding areas of South China. A total of 387 tilapia samples were collected including 24 suspected healthy, 35 moribund and 328 dead fish. The achieved detection rates were 0, 100 and 94·82% via bacteriological examination, and 0, 100 and 98·78% via qPCR assay respectively. The concentration of S. agalactiae in brain tissues ranged between 10⁵ and 10⁷  CFU per mg.

CONCLUSIONS

Streptococcus agalactiae can survive for 48 h in the brain of dead fish. Dead tilapia can be a useful alternative for epidemiological investigation when the diagnostic analysis of moribund fish is unavailable or impractical.

SIGNIFICANCE AND IMPACT OF THE STUDY

This detection method expands the sampling range, reduces the difficulty of sample collection and improves efficiency. Consequently, this method provides an alternative for epidemiological investigation of tilapia streptococcosis.

Mucosal Vaccination with Lactococcus lactis-Secreting Surface Immunological Protein Induces Humoral and Cellular Immune Protection against Group B Streptococcus in a Murine Model

Group B Streptococcus (GBS) is the primary etiological agent of sepsis and meningitis in newborns and is associated with premature birth and stillbirth. The development of a licensed vaccine is one of the pending challenges for the World Health Organization. Previously, we showed that oral immunization with surface immune protein (SIP) decreases vaginal colonization of GBS and generates functional opsonizing antibodies, which was determined by opsonophagocytic assays (OPA) in vitro. We also showed that the protein has an adjuvant vaccine profile. Therefore, an oral vaccine based on SIP may be an attractive alternative to employ in the development of new vaccines against GBS. Lactococcus lactis is a highlighted oral vaccine probiotic inducer of the mucosal immune response. This bacterium could serve as an antigen-delivering vehicle for the development of an edible vaccine and has been used in clinical trials. In this study, we showed that an oral vaccine with a recombinant L. lactis strain secreting SIP from GBS (rL. lactis-SIP) can induce protective humoral and cellular immunity in an experimental model of GBS vaginal colonization in C57BL/6 mice. Mice immunized with rL. lactis-SIP were protected against clinical symptoms and bacterial colonization after GBS vaginal colonization. Our rL. lactis-SIP vaccine also induces an increase of immunoglobulin G (IgG) and immunoglobulin A (IgA) specifically against SIP. The adoptive transfer of serum from vaccinated mice to naïve mice generated protection against GBS vaginal colonization. Moreover, the rL.lactis-SIP strain induces the activation of SIP-specific T cells, which could decrease GBS vaginal colonization and generate protective antibodies when transferred to other mice. Our experimental observations strongly support the notion that rL. lactis-SIP induces protective humoral and cellular immunity and could be considered as a novel alternative in the development of vaccines for GBS.

α-Enolase as a novel vaccine candidate against Streptococcus dysgalactiae infection in cobia (Rachycentron canadum L.)

Streptococcus dysgalactiae is an important pathogenic bacterium that has caused economic loss for the cobia industry in Taiwan, ROC. This study presents a highly effective subunit vaccine composed of a moonlight protein, α-enolase, for the prevention of S. dysgalactiae infection. First, α-enolase was cloned, transformed, and expressed in E. coli for production of recombinant protein. Then, the protective efficacies of α-enolase recombinant protein were evaluated in combination with either a pro-inflammatory cytokine, TNF-α, or an oil adjuvant, ISA 763 AVG. The results showed that the combination of α-enolase and ISA 763 AVG was highly protective (RPS = 88.89%), while a negative effect was found in the group immunised with α-enolase adjuvanted with TNF-α (RPS = 22.22%). A further study was conducted with double dose of ISA 763 AVG, which led to an increased RPS value of 97.37%. Moreover, immunised cobia exhibited significantly greater lysozyme activity, antibody responses, and expression of certain immune-related genes post-challenge. Altogether, our results demonstrated that a combination of α-enolase recombinant protein with ISA 763 AVG adjuvant is a promising vaccine that can be employed for protection of cobia against S. dysgalactiae infection.

Novel Chimeric Multiepitope Vaccine for Streptococcosis Disease in Nile Tilapia (Oreochromis niloticus Linn.)

Streptococcus agalactiae is a causative agent of streptococcosis disease in various fish species, including Nile tilapia (Oreochromis niloticus Linn.). Vaccination is an effective disease prevention and control method, but limitations remain for protecting against catastrophic mortality of fish infected with different strains of streptococci. Immunoproteomics analysis of S. agalactiae was used to identify antigenic proteins and construct a chimeric multiepitope vaccine. Epitopes from five antigenic proteins were shuffled in five helices of a flavodoxin backbone, and in silico analysis predicted a suitable RNA and protein structure for protein expression. 45F2 and 42E2 were identified as the best candidates for a chimeric multiepitope vaccine. Recombinant plasmids were constructed to produce a recombinant protein vaccine and DNA vaccine system. Overexpressed proteins were determined to be 30 kDa and 25 kDa in the E. coli and TK1 systems, respectively. The efficacy of the chimeric multiepitope construct as a recombinant protein vaccine and DNA vaccine was evaluated in Nile tilapia, followed by S. agalactiae challenge at 1 × 107 CFU/mL. Relative percentage survival (RPS) and cumulative mortality were recorded at approximately 57-76% and 17-30%, respectively. These chimeric multiepitope vaccines should be applied in streptococcosis disease control and developed into a multivalent vaccine to control multiple diseases.

Development of an attenuated oral vaccine strain of tilapia Group B Streptococci serotype Ia by gene knockout technology

Our previous studies demonstrated that the deletion of D2 fragment in tilapia Streptococcus agalactiae(GBS) attenuated strain YM001 is the main reason for the loss of virulence to tilapia. In this study, a Δ2 mutant that deletion of D2 fragment in parental virulent strain HN016 was constructed, and the safety, stability, immunogenicity, and growth characteristics, as well as the virulence mechanism of Δ2 mutant were evaluated. The results showed that Δ2 mutant was not pathogenic to tilapia, and the virulent revertants were not observed after 50 generations of passage. The RPS reached 96.11% at 15 days and 93.05% at 30 days, respectively, after intraperitoneal injection, while RPS reached 74.80% at 15 days and 53.16% at 30 days, respectively, after oral immunization. The growth of Δ2 mutant was significantly faster than YM001, and genes that were enriched in the nitrogen metabolism and arginine biosynthesis signaling pathway (arc, glnA, and gdhA) were identified as important candidate genes responsible for growth rate of S. agalactiae. The absence of D2 fragment affected the expression of Sip, therefore influencing the bacterial virulence. Altogether, this study demonstrated that deletion of D2 fragment in HN016 causes the loss of virulence to tilapia, and Δ2 mutant is a promising, better attenuated oral vaccine strain of S. agalactiae compared to YM001.

The correlation between expression of sip protein in different serotypes of group b streptococcus and diagnosis

Since the surface immunogenic protein (Sip) of group B streptococcus was identified, it's immunogenicity and its potential as a universal vaccine candidate has been evaluated extensively. We developed recombinant Sip protein and used it for monoclonal antibody generation to develop immunochromatographic test kit for GBS detection. The test of bacteria and culture media revealed the correlation between Sip protein expression and diagnosis discrepancy, which has never been reported. Furthermore, not only the surface accessibility of the Sip protein may vary from strains or serotypes; the secretion level of Sip protein may also vary.

Cellular immune response induced by surface immunogenic protein with AbISCO-100 adjuvant vaccination decreases group B Streptococcus vaginal colonization

Group B Streptococcus (GBS) represents one of the most common causes of bacterial infection in neonates; it is also associated with premature childbirth and stillbirth. A vaccine against GBS is needed, but no approved vaccines are yet available. The Surface Immunogenic Protein (SIP) of GBS is conserved in all serotypes and had been reported to be a good vaccine prototype in a mouse model of GBS infection. Also, we have previously shown that both subcutaneous and oral immunization with rSIP can induce an efficient immune response that decreases GBS vaginal colonization in mice. In this study, we show that a vaccine based on a mixture of rSIP and AbISCO-100 adjuvant reduces GBS vaginal colonization in mice and induces antibodies with opsonophagocytic activities. Moreover, the passive transfer of sera and total T-cells from mice immunized with rSIP mixed with AbISCO-100 to unvaccinated mice decreases vaginal GBS colonization in an infected mouse. This is the first report of cellular immunity associated with rSIP-based vaccine testing in a mouse model of GBS infection.

Surface Structures of Group B Streptococcus Important in Human Immunity

The surface of the Gram-positive opportunistic pathogen Streptococcus agalactiae, or group B Streptococcus (GBS), harbors several carbohydrate and protein antigens with the potential to be effective vaccines. Capsular polysaccharides of all clinically-relevant GBS serotypes coupled to immunogenic proteins of both GBS and non-GBS origin have undergone extensive testing in animals that led to advanced clinical trials in healthy adult women. In addition, GBS proteins either alone or in combination have been tested in animals; a fusion protein construct has recently advanced to human clinical studies. Given our current understanding of the antigenicity and immunogenicity of the wide array of GBS surface antigens, formulations now exist for the generation of viable vaccines against diseases caused by GBS.

Oral vaccination of tilapia against Streptococcus agalactiae using Bacillus subtilis spores expressing Sip

Streptococcus agalactiae infections are becoming an increasing problem in aquaculture because of significant morbidity and mortality, which restricts the healthy development of tilapia aquaculture. To seek safe and effective prevention measures, a Bacillus subtilis GC5 surface displayed vaccine was prepared and applied orally in tilapia. The study first showed that recombinant spores can engraft in the tilapia intestine. Then, the effect of protection and the immune responses were evaluated. The results of ELISA showed that Sip-specific antibody in the sera of GC5-Sip-immunized fish can be detected after the first oral administration when compared to the phosphate buffer saline (PBS) control group, and the levels of specific IgM gradually strengthened with boosting, so does the specific antibody against bacteria, proving that humoral immunity was induced. Quantitative real-time PCR (qRT-PCR) results showed that the immune-related gene expression of the gut and spleen exhibited a different rising trend in the GC5-Sip group, revealing that innate immune response and local as well as systemic cellular immunity were induced. The outcome of fish immunized with GC5-Sip spores provided a relative percent survival (RPS) of 41.7% against S. agalactiae and GC5 group had an RPS of 24.2%, indicating that GC5-Sip was safe and effective in protecting tilapia against bacterial infection. Our study demonstrated that the oral administration of B. subtilis spores expressing Sip could cause an effective immune response and offer good resistance to bacterial infection. Our work may lead to the development of new ideas for immunoprophylaxis against S. agalactiae infection.

Immunizing mice using different combination antigens of the PI-2a fimbria subunit of Streptococcus agalactiae

BACKGROUND

Streptococcus agalactiae is the main causal pathogen of bovine mastitis (BM), causing considerable economic loss to the dairy industry worldwide. Vaccines against S . agalactiae play an important role in preventing disease.

AIMS

The aim of this study was to evaluate the immunoprotection of S. agalactiae pilus island fusion proteins, ancillary protein 1-ancillary protein 2 (AP1-AP2), ancillary protein 1-bone protein (AP1-BP), bone protein-ancillary protein 2 (BP-AP2), and ancillary protein 1-bone protein-ancillary protein 2 (AP1-BP-AP2) in Balb/c mice.

METHODS

Four kinds of fusion antigens and the same volume of Freund's complete adjuvant were mixed vigorously to prepare fusion antigen immuno-samples. The mice were immunized 4 times (on the 0th, 7th, 14th, and 28th days) with these samples with an immunizing dose of 50 g/mouse. After the 4th immunization, serology tests were used to evaluate the antibody. The antibody titre produced by AP1-BP-AP2 fusion antigen was the highest, at up to 1:25600. The mice were then injected with 0.5 ml of 2 × 10⁴ CFU/ml clinically isolated S. agalactiae at day 50 and observed daily for the following 7 days.

RESULTS

Statistical analyses showed that these 4 kinds of fusion antigens had good protective immunity. Among them, AP1-BP-AP2 fusion antigen had the best protective immunity in Balb/c mice, with an immune protection index (PI) of 80%. Conclusion: This research provides a reliable theoretical basis for screening candidate antigens of the subunit vaccine and detecting antigen preparations of S. agalactiae.

Proteomics, Bioinformatics and Structure-Function Antigen Mining For Gonorrhea Vaccines

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the serious health consequences combined with the prevalence and the dire possibility of untreatable gonorrhea. Reverse vaccinology, which includes genome and proteome mining, has proven successful in the discovery of vaccine candidates against many pathogenic bacteria. Here, we describe proteomic applications including comprehensive, quantitative proteomic platforms and immunoproteomics coupled with broad-ranging bioinformatics that have been applied for antigen mining to develop gonorrhea vaccine(s). We further focus on outlining the vaccine candidate decision tree, describe the structure-function of novel proteome-derived antigens as well as ways to gain insights into their roles in the cell envelope, and underscore new lessons learned about the fascinating biology of Neisseria gonorrhoeae.

Oral vaccine based on a surface immunogenic protein mixed with alum promotes a decrease in Streptococcus agalactiae vaginal colonization in a mouse model

The Surface Immunogenic Protein (SIP) of Group B Streptococcus (GBS) had been described as a good target for vaccine development. To date, SIP has been reported as a highly conserved protein, and in a mouse model it induces protection against lethal GBS challenge. Also, similar effects have been described by intranasal immunization with a SIP-based vaccine. In this study, we show the immune response induced by an oral SIP-based vaccine formulated on alum in a mouse model. Our vaccine can reduce vaginal GBS colonization and induce specific SIP-antibodies with opsonophagocytosis activities against GBS. Moreover, we observed the activation of T-cells producing IFN-γ, TNF-α, IL-10, IL-2, and increased expression of the transcription factor T-bet, suggesting a Th1-type humoral response. The oral SIP-based vaccine is a novel alternative in the development of a vaccine against GBS.

The Optimisation of the Expression of Recombinant Surface Immunogenic Protein of Group B Streptococcus in Escherichia coli by Response Surface Methodology Improves Humoral Immunity

Group B Streptococcus (GBS) is the leading cause of neonatal meningitis and a common pathogen in livestock and aquaculture industries around the world. Conjugate polysaccharide and protein-based vaccines are under development. The surface immunogenic protein (SIP) is a conserved protein in all GBS serotypes and has been shown to be a good target for vaccine development. The expression of recombinant proteins in Escherichia coli cells has been shown to be useful in the development of vaccines, and the protein purification is a factor affecting their immunogenicity. The response surface methodology (RSM) and Box-Behnken design can optimise the performance in the expression of recombinant proteins. However, the biological effect in mice immunised with an immunogenic protein that is optimised by RSM and purified by low-affinity chromatography is unknown. In this study, we used RSM for the optimisation of the expression of the rSIP, and we evaluated the SIP-specific humoral response and the property to decrease the GBS colonisation in the vaginal tract in female mice. It was observed by NI-NTA chromatography that the RSM increases the yield in the expression of rSIP, generating a better purification process. This improvement in rSIP purification suggests a better induction of IgG anti-SIP immune response and a positive effect in the decreased GBS intravaginal colonisation. The RSM applied to optimise the expression of recombinant proteins with immunogenic capacity is an interesting alternative in the evaluation of vaccines in preclinical phase, which could improve their immune response.

Improving the Sensitivity of Real-time PCR Detection of Group B Streptococcus Using Consensus Sequence-Derived Oligonucleotides

Group B Streptococcus (GBS) is a perinatal pathogen and an emerging cause of disease in adults. Culture-independent GBS detection relies on polymerase chain reaction (PCR) of conserved genes, including sip. We demonstrate suboptimal sensitivity of the existing sip PCR strategy and validate an improved method based on consensus sequences from >100 GBS genomes.

Development of a melting-curve based multiplex real-time PCR assay for simultaneous detection of Streptococcus agalactiae and genes encoding resistance to macrolides and lincosamides

Background

Streptococcus agalactiae or Group B Streptococcus (GBS) remains the leading cause of infections in newborns worldwilde. Prenatal GBS screening of pregnant women for vaginal-rectal colonization is recommended in many countries to manage appropriate intrapartum antimicrobial prophylaxis for those identified as carriers. In this study, a novel melting-curve based multiplex real-time PCR assay for the simultaneous detection of GBS and macrolide and lincosamide resistance markers was developed. The usefulness of the assay was evaluated for rapid and accurate prenatal GBS screening.

Methods

One hundred two pregnant women who were at 35–37 weeks of gestation were enrolled in this study. The analytical performance of the multiplex real-time PCR was first tested using a panel of reference and clinical bacterial and fungal strains. To test the clinical performance, vaginal-rectal swabs were obtained from pregnant women who were seen at the teaching hospital for regular prenatal care. The results of real-time were compared with those obtained from microbiological analyses.

Results

The real-time PCR assay showed 100% specificity and a limit of detection of 10⁴ colony forming units equivalent per reaction. The prevalence of GBS colonization among the population studied was 15.7% (16/102) based on a positive culture and the real-time PCR results. Agreement between the two assays was found for 11 (68.75%) GBS colonized women. Using the culture-based results as a reference, the multiplex real-time PCR had a sensitivity of 91.7% (11/12, CI 59.7–99.6%), a specificity of 95.5% (86/90, CI 89.8–98.7%), a positive predictive value of 73.3% (11/15, CI 44.8–91.1%) and a negative predictive value of 98.9% (86/87, CI 92.9–99.9%).

Conclusion

The multiplex real-time PCR is a rapid, affordable and sensitive assay for direct detection of GBS in vaginal-rectal swabs.

Electronic supplementary material

The online version of this article (10.1186/s12884-018-1774-5) contains supplementary material, which is available to authorized users.

Effectivity of oral recombinant DNA vaccine against Streptococcus agalactiae in Nile tilapia

The effects of oral vaccination by two immune routes (gavage and mixed fodder administration) using a recombinant DNA vaccine SL7207-pVAX1-sip against Streptococcus agalactiae were assessed. SL7207-pVAX1-sip significantly enhanced various innate immune responses of tilapia, such as total serum protein, superoxide dismutase activity, lysozyme activity, complement C3 concentration in serum, serum antibacterial activity, and interleukin 1β and tumor necrosis factor-α. Vaccinated fish had higher relative percent survival values (57% and 63% for gavage group and mix fodder administration, respectively) at 10 weeks after S. agalactiae infection. When administered mixed fodder, the DNA vaccine SL7207-pVAX1-sip against S. agalactiae may produce more effective protection. These findings can promote the application and development of DNA vaccines in aquaculture.

Association between antibodies against group B Streptococcus surface proteins and recto-vaginal colonisation during pregnancy

Group B Streptococcus (GBS) recto-vaginal colonisation in pregnant women is the major risk factor for early-onset invasive GBS disease in their newborns. We aimed to determine the association between serum antibody levels against 11 GBS surface proteins and recto-vaginal acquisition of GBS colonisation during pregnancy. Sera collected from pregnant women at 20-25 weeks and ≥37 weeks of gestation age were measured for IgG titres against GBS surface proteins using  a multiplex immunoassay. Women were evaluated for recto-vaginal colonisation every 4-5 weeks. We observed that the likelihood of becoming colonised with GBS during pregnancy was lower in women with IgG titres ≥200 U/mL against gbs0233 (adjusted OR = 0.47 [95% CI: 0.25-0.89], p = 0.021) and ≥85 U/mL for gbs1539 (adjusted OR = 0.44 [95% CI: 0.24-0.82], p = 0.01) when comparing between women who acquired GBS colonisation and those that remained free of GBS colonisation throughout pregnancy. IgG titres (U/mL) specific to BibA and Sip were higher in pregnant women colonised with GBS (380.19 and 223.87, respectively) compared to women with negative GBS cultures (234.42 and 186.21, respectively; p < 0.01) at ≥37 weeks gestation. Antibodies induced by gbs0233 and gbs1539 were associated with a reduced likelihood of recto-vaginal GBS acquisition during pregnancy and warrant further investigation as vaccine targets.

Mucosal vaccination promotes clearance of Streptococcus agalactiae vaginal colonization

Group B Streptococcus (GBS) is a leading cause of morbidity and mortality in infants, and colonization of the maternal genital tract is the primary risk factor for newborn infection. Despite the importance of mucosal colonization in GBS pathogenesis, relevant host and bacterial factors are incompletely understood. We investigated the role of humoral immunity in clearance of vaginal colonization in vivo. B-cell-deficient mice or those lacking neonatal Fc-receptor, a mediator of IgG transport to the vaginal mucosa, exhibit prolonged GBS vaginal colonization compared to wild type animals. Intranasal but not intramuscular immunization induced systemic and mucosal immune responses and decreased GBS colonization duration without altering initial colonization density. Vaccine-induced clearance of GBS was serotype-specific, suggesting a role for anti-capsule antibodies in protection. Our results support a role for humoral immunity in GBS eradication from the female genital tract and suggest that mucosal vaccination may prime colonization clearance.

An Overview of Vaccination Strategies and Antigen Delivery Systems for Streptococcus agalactiae Vaccines in Nile Tilapia (Oreochromis niloticus)

Streptococcus agalactiae is an emerging infectious disease adversely affecting Nile tilapia (Niloticus oreochromis) production in aquaculture. Research carried out in the last decade has focused on developing protective vaccines using different strategies, although no review has been carried out to evaluate the efficacy of these strategies. The purpose of this review is to provide a synopsis of vaccination strategies and antigen delivery systems currently used for S. agalactiae vaccines in tilapia. Furthermore, as shown herein, current vaccine designs include the use of replicative antigen delivery systems, such as attenuated virulent strains, heterologous vectors and DNA vaccines, while non-replicative vaccines include the inactivated whole cell (IWC) and subunit vaccines encoding different S. agalactiae immunogenic proteins. Intraperitoneal vaccination is the most widely used immunization strategy, although immersion, spray and oral vaccines have also been tried with variable success. Vaccine efficacy is mostly evaluated by use of the intraperitoneal challenge model aimed at evaluating the relative percent survival (RPS) of vaccinated fish. The major limitation with this approach is that it lacks the ability to elucidate the mechanism of vaccine protection at portals of bacterial entry in mucosal organs and prevention of pathology in target organs. Despite this, indications are that the correlates of vaccine protection can be established based on antibody responses and antigen dose, although these parameters require optimization before they can become an integral part of routine vaccine production. Nevertheless, this review shows that different approaches can be used to produce protective vaccines against S. agalactiae in tilapia although there is a need to optimize the measures of vaccine efficacy.

Natural acquired group B Streptococcus capsular polysaccharide and surface protein antibodies in HIV-infected and HIV-uninfected children

Group B Streptococcus (GBS) is a major cause of invasive disease in young infants and also in older immunocompromised individuals, including HIV-infected persons. We compared naturally acquired antibody titres to GBS polysaccharide and surface protein antigens in HIV-uninfected and HIV-infected children aged 4-7 years. A multiplex Luminex immunoassay was used to measure IgG concentrations against GBS capsular polysaccharides (CPS) for serotypes Ia, Ib, III and V; and also extracellular localizing proteins which included cell-wall anchored proteins: Fibrinogen binding surface Antigen (FbsA), GBS Immunogenic Bacterial Adhesin (BibA), Surface immunogenic protein (Sip), gbs0393, gbs1356, gbs1539, gbs0392; and lipoproteins gbs0233, gbs2106 and Foldase PsrA. HIV-infected children (n=68) had significantly lower IgG GMT compared to HIV-uninfected (n=77) children against CPS of serotype Ib (p=0.012) and V (p=0.0045), and surface proteins Sip (p<0.001) and gbs2106 (p=0.0014). IgG GMT against GBS surface proteins: FbsA, gbs1539, gbs1356, gbs0392, gbs0393 and Foldase PsrA were significantly higher in HIV-infected children (p<0.004). Moreover, amongst HIV infected children, IgG GMT to GBS surface proteins were higher in those with CD4⁺ lymphocyte counts <500cell/μL compared to those who had CD4⁺ lymphocyte count ⩾500cell/μL with the exception of Sip. The increased susceptibility to invasive GBS disease in HIV-infected individuals could be due to the lower serotype specific capsular antibody and possibly due to lower antibody to some of the GBS proteins such as Sip and gbs2106.

Major surfome and secretome profile of Streptococcus agalactiae from Nile tilapia (Oreochromis niloticus): Insight into vaccine development

Streptococcus agalactiae is a major piscine pathogen that is responsible for huge economic losses to the aquaculture industry. Safe recombinant vaccines, based on a small number of antigenic proteins, are emerging as the most attractive, cost-effective solution against S. agalactiae. The proteins of S. agalactiae exposed to the environment, including surface proteins and secretory proteins, are important targets for the immune system and they are likely to be good vaccine candidates. To obtain a precise profile of its surface proteins, S. agalactiae strain THN0901, which was isolated from tilapia (Oreochromis niloticus), was treated with proteinase K to cleave surface-exposed proteins, which were identified by liquid chromatography-tandem spectrometry (LC-MS/MS). Forty surface-associated proteins were identified, including ten proteins containing cell wall-anchoring motifs, eight lipoproteins, eleven membrane proteins, seven secretory proteins, three cytoplasmic proteins, and one unknown protein. In addition, culture supernatant proteins of S. agalactiae were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and all of the Coomassie-stained bands were subsequently identified by LC-MS/MS. A total of twenty-six extracellular proteins were identified, including eleven secretory proteins, seven cell wall proteins, three membrane proteins, two cytoplasmic proteins and three unknown proteins. Of these, six highly expressed surface-associated and secretory proteins are putative to be vaccine candidate of piscine S. agalactiae. Moreover, immunogenic secreted protein, a highly expressed protein screened from the secretome in the present study, was demonstrated to induce high antibody titer in tilapia, and it conferred protection against S. agalactiae, as evidenced by the relative percent survival (RPS) 48.61± 8.45%. The data reported here narrow the scope of screening protective antigens, and provide guidance in the development of a novel vaccine against piscine S. agalactiae.

Serotype IV Streptococcus agalactiae ST-452 has arisen from large genomic recombination events between CC23 and the hypervirulent CC17 lineages

Streptococcus agalactiae (Group B Streptococcus, GBS) causes life-threatening infections in newborns and adults with chronic medical conditions. Serotype IV strains are emerging both among carriers and as cause of invasive disease and recent studies revealed two main Sequence Types (STs), ST-452 and ST-459 assigned to Clonal Complexes CC23 and CC1, respectively. Whole genome sequencing of 70 type IV GBS and subsequent phylogenetic analysis elucidated the localization of type IV isolates in a SNP-based phylogenetic tree and suggested that ST-452 could have originated through genetic recombination. SNPs density analysis of the core genome confirmed that the founder strain of this lineage originated from a single large horizontal gene transfer event between CC23 and the hypervirulent CC17. Indeed, ST-452 genomes are composed by two parts that are nearly identical to corresponding regions in ST-24 (CC23) and ST-291 (CC17). Chromosome mapping of the major GBS virulence factors showed that ST-452 strains have an intermediate yet unique profile among CC23 and CC17 strains. We described unreported large recombination events, involving the cps IV operon and resulting in the expansion of serotype IV to CC23. This work sheds further light on the evolution of GBS providing new insights on the recent emergence of serotype IV.

A Streptococcus suis LysM domain surface protein contributes to bacterial virulence

Streptococcus suis (SS) is a major swine pathogen, as well as a zoonotic agent for humans. Numerous factors contribute to SS virulence, but the pathogenesis of SS infection is poorly understood. Here, we show that a novel SS surface protein containing a LysM at the N-terminus (SS9-LysM) contributes to SS virulence. Homology analysis revealed that the amino acid sequence of SS9-LysM from the SS strain GZ0565 shares 99.8-68.7% identity with homologous proteins from other SS strains and 41.2% identity with Group B Streptococcal protective antigen Sip. Immunization experiments showed that 7 out of 30 mice immunized with recombinant SS9-LysM were protected against challenge with the virulent GZ0565 strain, while all of the control mice died within 48h following bacterial challenge. In mouse infection model, the virulence of the SS9-LysM deletion mutant (ΔSS9-LysM) was reduced compared with the wild-type (WT) strain GZ0565 and SS9-LysM complemented strain. In addition, ΔSS9-LysM was significantly more sensitive to killing by pig blood ex vivo and mouse blood in vivo compared with the WT strain and SS9-LysM complemented strain. In vivo transcriptome analysis in mouse blood showed that the WT strain reduced the expression of host genes related to iron-binding by SS9-LysM. Moreover, the total free iron concentration in blood from infected mice was significantly lower for the ΔSS9-LysM strain compared with the WT strain. Together, our data reveal that SS9-LysM facilitates SS survival within blood by releasing more free iron from the host. This represents a new mechanism of SS pathogenesis.

Group B Streptococcus vaccine: state of the art

Group B Streptococcus (GBS) is cause of neonatal invasive diseases as well as of severe infections in the elderly and immune-compromised patients. Despite significant advances in the prevention and treatment of neonatal disease, sepsis and meningitis caused by GBS still represent a significant public health care concern globally and additional prevention and therapeutic strategies against infection are highly desirable. The introduction of national recommended guidelines in several countries to screen pregnant women for GBS carriage and the use of antibiotics during delivery significantly reduced disease occurring within the first hours of life (early-onset disease), but it has had no effect on the late-onset diseases occurring after the first week and is not feasible in most countries. Availability of an effective vaccine against GBS would provide an effective means of controlling GBS disease. This review provides an overview of the burden of invasive disease caused by GBS in infants and adults, and highlights the strategies for the development of an effective vaccine against GBS infections.

Characterization of Isolates of Streptococcus agalactiae from Diseased Farmed and Wild Marine Fish from the U.S. Gulf Coast, Latin America, and Thailand

We examined Lancefield serogroup B Streptococcus isolates recovered from diseased, cultured hybrid Striped Bass (Striped Bass Morone saxatilis × White Bass M. chrysops) and wild and cultured Gulf Killifish Fundulus grandis from coastal waters of the U.S. Gulf of Mexico (Gulf coast) and compared those isolates to strains from tilapias Oreochromis spp. reared in Mississippi, Thailand, Ecuador, and Honduras and to the original Gulf coast strain identified by Plumb et al. ( 1974 ). The isolates were subjected to phylogenetic, biochemical, and antibiotic susceptibility analyses. Genetic analysis was performed using partial sequence comparison of (1) the 16S ribosomal RNA (rRNA) gene; (2) the sipA gene, which encodes a surface immunogenic protein; (3) the cspA gene, which encodes a cell surface-associated protein; and (4) the secY gene, which encodes components of a general protein secretion pathway. Phylogenies inferred from sipA, secY, and cspA gene sequence comparisons were more discriminating than that inferred from the 16S rRNA gene sequence comparison. The U.S. Gulf coast strains showed a high degree of similarity to strains from South America and Central America and belonged to a unique group that can be distinguished from other group B streptococci. In agreement with the molecular findings, biochemical and antimicrobial resistance analyses demonstrated that the isolates recovered from the U.S. Gulf coast and Latin America were more similar to each other than to isolates from Thailand. Three laboratory challenge methods for inducing streptococcosis in Gulf Killifish were evaluated-intraperitoneal (IP) injection, immersion (IMM), and immersion plus abrasion (IMMA)-using serial dilutions of S. agalactiae isolate LADL 97-151, a representative U.S. Gulf coast strain. The dose that was lethal to 50% of test fish by 14 d postchallenge was approximately 2 CFU/fish via IP injection. In contrast, the fish that were challenged via IMM or IMMA presented cumulative mortality less than 40% by 14 d postchallenge.

Development of an indirect ELISA for bovine mastitis using Sip protein of Streptococcus agalactiae

The sip gene encoding for a conserved highly immunogenic surface protein of Streptococcus agalactiae was amplified using polymerase chain reaction (PCR) and subcloned into prokaryotic expression vector pET32a (+) and expressed as a recombinant protein in E. coli BL21 (DE3). An indirect enzyme linked immunosorbent assay (ELISA) was developed using the purified Sip protein as a coating antigen, which could identify S. agalactiae specific antibody in sera. The coating antigen at a concentration of 3.125 μg/ml, serum diluted to 1:160, and HRP-conjugated secondary antibody concentration at 1:4000 was found to be most effective in exhibiting positive result. The ELISA was found to be highly specific for S. agalactiae that may be used for the detection of the pathogen in mastitis cases, for epidemiological studies and for surveillance.

Cloning and expression of a surface immunogenic protein in Streptococcus dysgalactiae isolated from fish and its application in enzyme-linked immunosorbent assays to diagnose S. dysgalactiae infections in fish

Lancefield group C Streptococcus dysgalactiae (GCSD) causes severe necrotic lesions in the caudal peduncle in the genus Seriola farmed in Japan. To develop a sero-diagnostic method for GCSD infection in farmed fish, we attempted to identify a surface immunogenic protein that induces an antibody after infection with GCSD by immunoblot analysis using sera collected from infected fish. A protein obtained from sodium dodecyl sulfate (SDS) extracts of GCSD was identified as S. dysgalactiae surface immunogenic protein (Sd-Sip). Sd-Sip exhibited more than 94% homology with a surface antigen or a hypothetical protein from S. dysgalactiae mammalian isolates at the nucleotide sequence level. Expression of the recombinant Sd-Sip (rSd-Sip) was confirmed by immunoblot analysis, that is, its reactivity to GCSD-infected sera. Antibody detection ELISA using rSd-Sip and their usefulness for diagnosis of GCSD infection were examined. GCSD-infected sera collected from farmed amberjack, Seriola dumerili (Risso), showed strong reaction with immobilized rSd-Sip. Meanwhile, sera immunized by other pathogenic bacteria of fish were showed ELISA values similar to those of non-infected sera. These results of this study suggest that the antibody detection ELISA using rSd-Sip is an effective diagnostic method for GCSD infection in fish.

A recombinant truncated surface immunogenic protein (tSip) plus adjuvant FIA confers active protection against Group B streptococcus infection in tilapia

PURPOSE

Tilapia is an important agricultural fish that has been plagued by Group B streptococcus (GBS) infections in recent years, some of them severe. It is well-known that surface immunogenicity protein (Sip) is an effective vaccine against GBS.

EXPERIMENTAL DESIGN

Since Sip was not expressed in either E. coli BL21 or E. coli Rosetta, we removed the N-terminal signal peptide and LysM of the virus to produce purified truncated Sip (tSip(1)), which multiplied easily in an E. coli host. The antibody's ability to recognize and combine with GBS was determined by Western-blot and specific staining in vitro. The relative percentage of survival (RPS), antibody titers, bacterial recovery, and pathologic morphology were monitored in vivo to evaluate the immune effects. Freund's incomplete adjuvant (FIA) plus tSip and aluminum hydroxide gel (AH) plus tSip were also evaluated.

RESULTS

It revealed that tSip mixed with FIA was an effective vaccine against GBS in tilapia, while AH is toxic to tilapia.

Association and virulence gene expression vary among serotype III group B streptococcus isolates following exposure to decidual and lung epithelial cells

Group B Streptococcus (GBS) causes severe disease in neonates, the elderly, and immunocompromised individuals. GBS species are highly diverse and can be classified by serotype and multilocus sequence typing. Sequence type 17 (ST-17) strains cause invasive neonatal disease more frequently than strains of other STs. Attachment and invasion of host cells are key steps in GBS pathogenesis. We investigated whether four serotype III strains representing ST-17 (two strains), ST-19, and ST-23 differ in their abilities to attach to and invade both decidual cells and lung epithelial cells. Virulence gene expression following host cell association and exposure to amnion cells was also tested. The ST-17 strains differed in their abilities to attach to and invade decidual cells, whereas there were no differences with lung epithelial cells. The ST-19 and ST-23 strains, however, attached to and invaded decidual cells less than both ST-17 strains. Although the ST-23 strain attached to lung epithelial cells better than ST-17 and -19 strains, none of the strains effectively invaded the lung epithelial cells. Notably, the association with host cells resulted in the differential expression of several virulence genes relative to basal expression levels. Similar expression patterns of some genes were observed regardless of cell type used. Collectively, these results show that GBS strains differ in their abilities to attach to distinct host cell types and express key virulence genes that are relevant to the disease process. Enhancing our understanding of pathogenic mechanisms could aid in the identification of novel therapeutic targets or vaccine candidates that could potentially decrease morbidity and mortality associated with neonatal infections.

Safety and immunogenicity of an oral DNA vaccine encoding Sip of Streptococcus agalactiae from Nile tilapia Oreochromis niloticus delivered by live attenuated Salmonella typhimurium

Attenuated Salmonella typhimurium SL7207 was used as a carrier for a reconstructed DNA vaccine against Streptococcus agalactiae. A 1.02 kb DNA fragment, encoding for a portion of the surface immunogenic protein (Sip) of S. agalactiae was inserted into pVAX1. The recombinant plasmid pVAX1-sip was transfected in EPC cells to detect the transient expression by an indirect immunofluorescence assay, together with Western blot analysis. The pVAX1-sip was transformed by electroporation into SL7207. The stability of pVAX1-sip into Salmonella was over 90% after 50 generations with antibiotic selection in vitro while remained stable over 80% during 35 generations under antibiotic-free conditions. The LD50 of SL/pVAX1-sip was 1.7 × 10(11) CFU/fish by intragastric administration which indicated a quite low virulence. Tilapias were inoculated orally at 10(8) CFU/fish, the recombinant bacteria were found present in intestinal tract, spleens and livers and eventually eliminated from the tissues 4 weeks after immunization. Fish immunized at 10(7), 10(8) and 10(9) CFU/fish with different immunization times caused various levels of serum antibody and an effective protection against lethal challenge with the wild-type strain S. agalactiae. Integration studies showed that the pVAX1-sip did not integrate with tilapia chromosomes. The DNA vaccine SL/pVAX1-sip was proved to be safe and effective in protecting tilapias against S. agalactiae infection.

Group B streptococcal epidemiology and vaccine needs in developed countries

Development of a group B streptococcal vaccine (GBS) vaccine is the most promising approach for the prevention of GBS infections in babies, given the potential adverse effects of intrapartum antibiotic prophylaxis as well as the need for effective prevention of both adult and late perinatal disease. There are numerous prevention strategies at this time but none are 100% effective in the eradication of neonatal early onset GBS disease and there are no preventative strategies for late onset disease. The need for a GBS vaccine is therefore, of utmost importance. Efforts applying genomics to GBS vaccine development have led to the identification of novel vaccine candidates. The publication of GBS whole genomes coupled with new technologies including multigenome screening and bioinformatics has also allowed researchers to overcome the serotype limitation of earlier vaccine preparations in the search of a universal effective vaccine against GBS. This review brings together the key arguments concerning the potential need of a GBS vaccine in developed countries and describes the current status with GBS epidemiology and microbiology in these countries.