Development of experimental GBS vaccine for mucosal immunization

Streptococcus agalactiae, or group B streptococcus (GBS), is an important pathogen as it is the leading cause of neonatal deaths due to sepsis, meningitis or bacterial pneumonia. Although the development of an effective and safe GBS vaccine is on the agenda of many research labs, there is no GBS vaccine on the market yet. In the present study we attempted to engineer a live vaccine strain based on Bac, a surface protein of GBS, incorporated into a surface fimbrial protein of probiotic Enterococcus. The resulting strain induced specific systemic and local immune responses in mice and provided protection against GBS when administered via the intranasal, oral or intravaginal immunization routes.

Use of Proteins Identified through a Functional Genomic Screen To Develop a Protein Subunit Vaccine That Provides Significant Protection against Virulent Streptococcus suis in Pigs

Streptococcus suis is a bacterium that is commonly carried in the respiratory tract and that is also one of the most important invasive pathogens of swine, commonly causing meningitis, arthritis, and septicemia. Due to the existence of many serotypes and a wide range of immune evasion capabilities, efficacious vaccines are not readily available. The selection of S. suis protein candidates for inclusion in a vaccine was accomplished by identifying fitness genes through a functional genomics screen and selecting conserved predicted surface-associated proteins. Five candidate proteins were selected for evaluation in a vaccine trial and administered both intranasally and intramuscularly with one of two different adjuvant formulations. Clinical protection was evaluated by subsequent intranasal challenge with virulent S. suis While subunit vaccination with the S. suis proteins induced IgG antibodies to each individual protein and a cellular immune response to the pool of proteins and provided substantial protection from challenge with virulent S. suis, the immune response elicited and the degree of protection were dependent on the parenteral adjuvant given. Subunit vaccination induced IgG reactive against different S. suis serotypes, indicating a potential for cross protection.

GapA, a potential vaccine candidate antigen against Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus)

Streptococcosis due to the bacterium Streptococcus agalactiae (S. agalactiae) has resulted in enormous economic losses in aquaculture worldwide, especially in the tilapia culture industry. Previously, there were limited vaccines that could be employed against streptococcosis in tilapia. This study aimed to develop a vaccine candidate using the glyceraldehyde-phosphate dehydrogenase protein (GapA) of S. agalactiae encoded by the gapA gene. Tilapia were intraperitoneally injected with PBS, PBS + Freund's adjuvant, PBS + Montanide's adjuvant, GapA + Freund's adjuvant, GapA + Montanide's adjuvant, killed S. agalactiae whole cells (WC)+Freund's adjuvant, or killed S. agalactiae whole cells (WC)+ Montanide's adjuvant. They were then challenged with S. agalactiae, and the relative percentage survival (RPS) was monitored 14 days after the challenge. The highest RPSs were observed in the WC groups, with 76.7% in WC + Freund's adjuvant and 74.4% in WC + Montanide's adjuvant groups; these were followed by the GapA groups, with 63.3% in GapA + Freund's adjuvant and 45.6% in GapA + Montanide's adjuvant groups. The RPS of the PBS group was 0%, and those of PBS + Freund's adjuvant and PBS + Montanide's adjuvant groups were 6.7% and 3.3%, respectively. Additionally, the IgM antibody responses elicited in GapA groups and WC groups were significantly higher than those in PBS groups. Furthermore, the expressions of cytokine (IL-1β and TNF-α) mRNAs in the GapA groups and WC groups were significantly higher than those in the PBS groups. Taken together, these results reveal that the GapA protein is a promising vaccine candidate that could be used to prevent streptococcosis in tilapia.

Deletion of ssnA Attenuates the Pathogenicity of Streptococcus suis and Confers Protection against Serovar 2 Strain Challenge

Streptococcus suis serotype 2 (SS2) is a major porcine and human pathogen which causes arthritis, meningitis, and septicemia. Streptococcus suis nuclease A (SsnA) is a recently discovered deoxyribonuclease (DNase), which has been demonstrated to contribute to escape killing in neutrophil extracellular traps (NETs). To further determine the effects of ssnA on virulence, the ssnA deletion mutant (ΔssnA) and its complemented strain (C-ΔssnA) were constructed. The ability of ΔssnA mutant to interact with human laryngeal epithelial cell (Hep-2) was evaluated and it exhibited dramatically decreased ability to adhere to and invade Hep-2 cells. This mutation was found to exhibit significant attenuation of virulence when evaluated in CD1 mice, suggesting ssnA plays a critical role in the pathogenesis of SS2. Finally, we found that immunization with the ΔssnA mutant triggered both antibody responses and cell-mediated immunity, and conferred 80% protection against virulent SS2 challenge in mice. Taken together, our results suggest that ΔssnA represents an attractive candidate for designing an attenuated live vaccine against SS2.

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.

Pellet feed adsorbed with the recombinant Lactococcus lactis BFE920 expressing SiMA antigen induced strong recall vaccine effects against Streptococcus iniae infection in olive flounder (Paralichthys olivaceus)

The aim of this study was to develop a fish feed vaccine that provides effective disease prevention and convenient application. A lactic acid bacterium (LAB), Lactococcus lactis BFE920, was modified to express the SiMA antigen, a membrane protein of Streptococcus iniae. The antigen was engineered to be expressed under the nisin promoter, which is induced by nisin produced naturally by the host LAB. Various sizes (40 ± 3.5 g, 80 ± 2.1 g, and 221 ± 2.4 g) of olive flounder (Paralichthys olivaceus) were vaccinated by feeding the extruded pellet feed, onto which the SiMA-expressing L. lactis BFE920 (1.0 × 10(7) CFU/g) was adsorbed. Vaccine-treated feed was administered twice a day for 1 week, and priming and boosting were performed with a 1-week interval in between. The vaccinated fish had significantly elevated levels of antigen-specific serum antibodies and T cell marker mRNAs: CD4-1, CD4-2, and CD8a. In addition, the feed vaccine significantly induced T cell effector functions, such as the production of IFN-γ and activation of the transcription factor that induces its expression, T-bet. When the flounder were challenged by intraperitoneal infection and bath immersion with S. iniae, the vaccinated fish showed 84% and 82% relative percent survival (RPS), respectively. Furthermore, similar protective effects were confirmed even 3 months after vaccination in a field study (n = 4800), indicating that this feed vaccine elicited prolonged duration of immunopotency. In addition, the vaccinated flounder gained 21% more weight and required 16% less feed to gain a unit of body weight compared to the control group. The data clearly demonstrate that the L. lactis BFE920-SiMA feed vaccine has strong protective effects, induces prolonged vaccine efficacy, and has probiotic effects. In addition, this LAB-based fish feed vaccine can be easily used to target many different pathogens of diverse fish species.

FbsC, a novel fibrinogen-binding protein, promotes Streptococcus agalactiae-host cell interactions

Streptococcus agalactiae (group B Streptococcus or GBS) is a common cause of invasive infections in newborn infants and adults. The ability of GBS to bind human fibrinogen is of crucial importance in promoting colonization and invasion of host barriers. We characterized here a novel fibrinogen-binding protein of GBS, designated FbsC (Gbs0791), which is encoded by the prototype GBS strain NEM316. FbsC, which bears two bacterial immunoglobulin-like tandem repeat domains and a C-terminal cell wall-anchoring motif (LPXTG), was found to be covalently linked to the cell wall by the housekeeping sortase A. Studies using recombinant FbsC indicated that it binds fibrinogen in a dose-dependent and saturable manner, and with moderate affinity. Expression of FbsC was detected in all clinical GBS isolates, except those belonging to the hypervirulent lineage ST17. Deletion of fbsC decreases NEM316 abilities to adhere to and invade human epithelial and endothelial cells, and to form biofilm in vitro. Notably, bacterial adhesion to fibrinogen and fibrinogen binding to bacterial cells were abolished following fbsC deletion in NEM316. Moreover, the virulence of the fbsC deletion mutant and its ability to colonize the brain were impaired in murine models of infection. Finally, immunization with recombinant FbsC significantly protected mice from lethal GBS challenge. In conclusion, FbsC is a novel fibrinogen-binding protein expressed by most GBS isolates that functions as a virulence factor by promoting invasion of epithelial and endothelial barriers. In addition, the protein has significant immunoprotective activity and may be a useful component of an anti-GBS vaccine.

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.

Towards a universal group BStreptococcusvaccine using multistrain genome analysis

Genomics has revolutionized the way in which novel vaccine candidates are identified for the development of efficacious vaccines. Reverse vaccinology, whereby all candidates of interest are identified by analysis of a pathogen's genome, enables characterization of many candidates simultaneously. It accelerates the initial steps of vaccine development and greatly increases the chances of obtaining reliable candidates or cocktails thereof. The availability of one or two genome sequences for any given pathogen provides access to strain-specific vaccine candidates but often fails to identify candidates that would confer general protection. The analysis of multiple genomes of group B Streptococcus revealed tremendous diversity and identified candidates that are not shared by all the strains sequenced, but provide general protection when combined.

[Intranasal co-administration of recombinant streptococcus group B polypeptides and influenza deltaNS1 vaccine]

In the present work, the immunoadjuvant properties of the influenza deltaNS1 vaccine virus after intranasal administration in combination with recombinant GBS polypeptides was tested in mice. According to our data, co-administration of recombinant GBS polypeptides and influenza deltaNS1 vaccine resulted in the increase in the immunogenicity and protective efficacy of bacterial proteins. Combined vaccination with the GBS polypeptides and influenza deltaNS1 vaccine has a potential to be used not only for prophylaxis infections caused by SGB, but also for prevention of the bacterial complications of influenza.

Streptococcal emm types in Hawaii: a region with high incidence of acute rheumatic fever

BACKGROUND

The clinical epidemiology of group A streptococcal (GAS) infections in Hawaii seems different from that in the continental United States with frequent skin infections and endemically high rates of acute rheumatic fever (ARF).

METHODS

GAS emm types in Hawaii were determined to identify any possible association between the emm types and specific clinical manifestations. A convenience sample of 1482 Hawaii GAS isolates collected between February 2000 and December 2005 was used. All isolates were characterized by emm sequence typing. The distribution of emm types in Hawaii was compared with the published continental US data for pharyngeal and invasive GAS strains, the CDC database from similar time periods, as well as with emm types present in a candidate GAS vaccine.

RESULTS

Ninety-three distinct emm types were recognized among the 1482 GAS isolates. The most frequently identified emm types in order of decreasing frequency were 12, 1, 28, 4, 22, 77, 81, 58, 65/69, 49, 74, 85, 92, 75, 101 and 2. Of this study sample, 27 of the 50 invasive GAS isolates belonged to uncommon continental US emm types (54% in Hawaii cultures vs. 10% reported from the continental US). Of the 1179 pharyngeal isolates, 509 belonged uncommon continental US emm types (43% in Hawaii cultures vs. 27% reported from the continental US).

CONCLUSIONS

The prevalent emm types in Hawaii differ from those in the continental US. The prevalence of these unusual emm types might limit the effectiveness of any proposed multivalent type-specific GAS vaccine in Hawaii.

Enhancement of salivary IgA response to a DNA vaccine against Streptococcus mutans wall-associated protein A in mice by plasmid-based adjuvants

A specific salivary IgA (sIgA) response was obtained in mice by intranasal immunization with a naked DNA vaccine consisting of the Streptococcus mutans wall-associated protein A gene (wapA) inserted into the mammalian expression vector pcDNA3.1/V5/His-TOPO. In the present study, the vaccine, referred to as pcDNA-wapA, was administered with or without the cationic lipid DMRIE-C. No mucosal response was observed in mice immunized with the vaccine alone, whereas a weak and temporal sIgA response was obtained when the vaccine was mixed with DMRIE-C. To investigate the use of pcDNA containing the interleukin 5 (IL-5) gene (pcDNA-il-5) or the cholera toxin B gene (pcDNA-ctb) as genetic adjuvants, these constructs were used in co-immunization studies. The enhancement effect was transient with pcDNA-il-5, but longer lasting with pcDNA-ctb, thus supporting the use of the latter as a genetic adjuvant to DNA vaccine.

Active and passive immunizations with the streptococcal esterase Sse protect mice against subcutaneous infection with group A streptococci

The human pathogen group A Streptococcus (GAS) produces many secreted proteins that play important roles in GAS pathogenesis, including hydrolases that degrade proteins and nucleic acids. This study targets another kind of hydrolase, carboxylic esterase, with the objectives of identifying GAS esterase and determining whether it is a protective antigen. The putative esterase gene SPy1718 was cloned, and the recombinant protein (Sse) was prepared. Sse was detected in GAS culture supernatant, and patients with streptococcal pharyngitis seroconverted to Sse, indicating that Sse was produced in vivo and in vitro. Sse hydrolyzes p-nitrophenyl butyrate, and the residue (178)Ser is critical for this esterase activity. There are two Sse variant complexes according to the available genome databases, consistent with the previous finding of two antigenic Sse variants. Complex I includes serotypes M1, M2, M3, M5, M6, M12, and M18, whereas M4, M28, and M49 belong to complex II. Sse variants share >98% identity in amino acid sequence within each complex but have about 37% variation between the two groups. Active immunization with M1 Sse significantly protects mice against lethal subcutaneous infection with virulent M1 and M3 strains and inhibits GAS invasion of mouse skin tissue. Passive immunization with anti-Sse antiserum also significantly protects mice against subcutaneous GAS infection, indicating that the protection is mediated by Sse-specific antibodies. The results suggest that Sse plays an important role in tissue invasion and is an antigen protective in subcutaneous infection against GAS strains of more than one serotype.

Vaccination of horses against strangles using recombinant antigens from Streptococcus equi

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

Analysis of the transcriptome of group A Streptococcus in mouse soft tissue infection

Molecular mechanisms mediating group A Streptococcus (GAS)-host interactions remain poorly understood but are crucial for diagnostic, therapeutic, and vaccine development. An optimized high-density microarray was used to analyze the transcriptome of GAS during experimental mouse soft tissue infection. The transcriptome of a wild-type serotype M1 GAS strain and an isogenic transcriptional regulator knockout mutant (covR) also were compared. Array datasets were verified by quantitative real-time reverse transcriptase-polymerase chain reaction and in situ immunohistochemistry. The results unambiguously demonstrate that coordinated expression of proven and putative GAS virulence factors is directed toward overwhelming innate host defenses leading to severe cellular damage. We also identified adaptive metabolic responses triggered by nutrient signals and hypoxic/acidic conditions in the host, likely facilitating pathogen persistence and proliferation in soft tissues. Key discoveries included that oxidative stress genes, virulence genes, genes related to amino acid and maltodextrin utilization, and several two-component transcriptional regulators were highly expressed in vivo. This study is the first global analysis of the GAS transcriptome during invasive infection. Coupled with parallel analysis of the covR mutant strain, novel insights have been made into the regulation of GAS virulence in vivo, resulting in new avenues for targeted therapeutic and vaccine research.

Identification and characterization of an antigen I/II family protein produced by group A Streptococcus

Group A Streptococcus (GAS) is a gram-positive human bacterial pathogen that causes infections ranging in severity from pharyngitis to life-threatening invasive disease, such as necrotizing fasciitis. Serotype M28 strains are consistently isolated from invasive infections, particularly puerperal sepsis, a severe infection that occurs during or after childbirth. We recently sequenced the genome of a serotype M28 GAS strain and discovered a novel 37.4-kb foreign genetic element designated region of difference 2 (RD2). RD2 is similar in gene content and organization to genomic islands found in group B streptococci (GBS), the major cause of neonatal infections. RD2 encodes seven proteins with conventional gram-positive secretion signal sequences, six of which have not been characterized. Herein, we report that one of these six proteins (M28_Spy1325; Spy1325) is a member of the antigen I/II family of cell surface-anchored molecules produced by oral streptococci. PCR and DNA sequence analysis found that Spy1325 is very well conserved in GAS strains of distinct M protein serotypes. As assessed by real-time TaqMan quantitative PCR, the Spy1325 gene was expressed in vitro, and Spy1325 protein was present in culture supernatants and on the GAS cell surface. Western immunoblotting and enzyme-linked immunosorbent assays indicated that Spy1325 was produced by GAS in infected mice and humans. Importantly, the immunization of mice with recombinant Spy1325 fragments conferred protection against GAS-mediated mortality. Similar to other antigen I/II proteins, recombinant Spy1325 bound purified human salivary agglutinin glycoprotein. Spy1325 may represent a shared virulence factor among GAS, GBS, and oral streptococci.

Use ofLactococcus lactisExpressing Pili from Group BStreptococcusas a Broad‐Coverage Vaccine against Streptococcal Disease

Recent data indicate that the human pathogen group B Streptococcus (GBS) produces pilus-like structures encoded in genomic islands with similar organization to pathogenicity islands. On the basis of the amino acid sequence of their protein components, 3 different types of pili have been identified in GBS, at least 1 of which is present in all isolates. We recently demonstrated that recombinant pilus proteins protect mice from lethal challenge with GBS and are thus potential vaccine candidates. Here, we show that GBS pilin island 1, transferred into the nonpathogenic microorganism Lactococcus lactis, leads to pilus assembly. We also show that systemically or mucosally delivered Lactococcus expressing pilin island 1 protects mice from challenge with GBS isolates carrying pilus 1. Furthermore, lactococci engineered to express hybrid pili containing GBS pilus 1 and pilus 2 components confer protection against strains expressing either of the 2 pilus types. These data pave the way to the design of pilus-based, multivalent live vaccines against streptococcal pathogens.

Protective effect of vaccination with recombinant proteins from Streptococcus equi subspecies equi in a strangles model in the mouse

A mouse model resembling Streptococcus equi subspecies equi infection in the horse, strangles, was used to assess the protective effect of vaccination with selected recombinant proteins from S. equi subsp. equi. After challenge the infection was monitored by weight loss and by nasal colonisation with S. equi subsp. equi. Vaccination with a collagen-binding protein (CNE) and a collagen-like protein (SclC) resulted in protective antibodies, whereas a novel fibronectin-binding protein (FNEB) did not. Co-administration of CNE with EAG, a poorly immunogenic alpha2-macroglobulin-, albumin- and immunoglobulin G-binding protein, resulted in a significant synergistic effect and enhanced the protective immune response against EAG.

Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks

Improved understanding of the epidemiology of Streptococcus equi transmission requires sensitive and portable subtyping methods that can rationally discriminate between strains. S. equi is highly homogeneous and cannot be distinguished by multilocus enzyme electrophoretic or multilocus sequence-typing methods that utilize housekeeping genes. However, on sequence analysis of the N-terminal region of the SeM genes of 60 S. equi isolates from 27 strangles outbreaks, we identified 21 DNA codon changes. These resulted in the nonsynonymous substitution of 18 amino acids and allowed the assignment of S. equi strains to 15 distinct subtypes. Our data suggest the presence of multiple epitopes across this region that are subjected to selective immune pressure (nonsynonymous-synonymous substitution rate [d(N)/d(S)] ratio = 3.054), particularly during the establishment of long-term S. equi infection. We further report the application of SeM gene subtyping as a method to investigate potential cases of disease related to administration of a live attenuated S. equi vaccine. SeM gene subtyping successfully differentiated between the vaccine strain and field strains of S. equi responsible for concurrent disease. These results were confirmed by the development and application of a PCR diagnostic test, which identifies the aroA partial gene deletion present in the Equilis StrepE vaccine strain. Although the vaccine strain was found to be responsible for injection site lesions, all seven outbreaks of strangles investigated in recently vaccinated horses were found to be due to concurrent infection with wild-type S. equi and not due to reversion of the vaccine strain.

Clonal association between Streptococcus pneumoniae serotype 23A, circulating within the United States, and an internationally dispersed clone of serotype 23F

Streptococcus pneumoniae is an important pathogen in the United States and is associated with significant morbidity and mortality. Since the introduction of the seven-valent conjugate vaccine, a significant decline in pneumococcal disease has been reported. However, surveillance for pneumococcal disease remains essential, as the extent of cross protection against vaccine-related serotypes is still unclear. Further, any increase in non-vaccine-related serotypes also needs monitoring. We report on a new clonal association between a vaccine-related serotype, serotype 23A, obtained as part of the Active Bacterial Core surveillance, with an established internationally dispersed Pneumococcal Molecular Epidemiology Network (PMEN) clone, clone Colombia(23F)-26. Sixty-two isolates of serotype 23A collected from sterile sites during a 2-year period (2002 and 2003) were characterized. Twenty-one (34%) isolates were penicillin nonsusceptible, although none were fully resistant. Pulsed-field gel electrophoresis and multilocus sequence typing analysis showed that 24 (39%) of the serotype 23A isolates shared either genetic identity or high genetic relatedness with PMEN clone Colombia(23F)-26. Extensive variability was noted within the sequenced region of pbp2b in two penicillin-nonsusceptible isolates as well as in PMEN clone Colombia(23F)-26, suggesting that these isolates probably acquired penicillin resistance independently. The emergence of such new serotype and genotype associations highlights the dynamic nature of the pneumococcal population, necessitating continuous monitoring in the post-vaccine era.

Protection against group A streptococcal infection by vaccination with self-adjuvanting lipid core M protein peptides

We have investigated the lipid polylysine core peptide (LCP) system as a self-adjuvanting group A streptococcal (GAS) vaccine delivery approach. LCP constructs were synthesised incorporating peptides from the M protein conserved carboxy terminal C-repeat region, the amino terminal type-specific region and from both of these regions. Immunisation with the constructs without adjuvant led to the induction of peptide-specific serum IgG antibody responses, heterologous opsonic antibodies, and complete protection from GAS infection. These data indicate that protective immunity to GAS infection can be evoked using the self-adjuvanting LCP system, and point to the potential application of this system in human mucosal GAS vaccine development.

A GapC chimera retains the properties of the Streptococcus uberis wild-type GapC protein

The GapC products of Streptococcus agalactiae, Streptococcus dysgalactiae, and Streptococcus uberis share considerable homology at the DNA and amino acid levels. The high similarity at the protein level suggests that one GapC protein might be used as a single antigen to protect dairy cows against infections with the contagious S. agalactiae and the environmental S. dysgalactiae and S. uberis strains. Despite their similarities, immunization with the S. dysgalactiae GapC did not protect dairy cows from a challenge with S. uberis, suggesting the presence of regions in GapC that are involved in species-specific protection. To produce a single antigen that can be used to protect against all streptococcal mastitis infections, we constructed a GapC chimeric protein using the S. uberis GapC product as the backbone followed by non-conserved peptide regions from the S. agalactiae and S. dysgalactiae GapC proteins. We report that the chimeric GapC protein retains the enzymatic activity of the S. uberis GapC protein. In addition, we fused the chimera to the OmpF and LipoF transport sequences of Escherichia coli and the GapC chimeras were present in membrane fractions of E. coli. These extracts could be the basis of an antigen preparation for use in mastitis vaccines.

The exploitation of the genome in the search for determinants of virulence in Streptococcus uberis

Despite much success in the control of mastitis in dairy cattle, intramammary infection with Streptococcus uberis remains a threat to herd health. This organism is a frequent cause of mastitis worldwide. Recent advances in the ability to genetically manipulate this bacterium, coupled to the determination of a representative genome sequence have already enabled the investigation of certain aspects of disease pathogenesis. Further use of such technology coupled to reliable models of disease and post-genomic analysis will permit the elucidation of further interactions between pathogen and host. This additional information can be usefully targeted at identification of candidates for inclusion in effective vaccines. This communication reviews the current, reported progress using this technology for S. uberis.

Recombinant Streptococcus equi proteins protect mice in challenge experiments and induce immune response in horses

Horses that have undergone infection caused by Streptococcus equi subspecies equi (strangles) were found to have significantly increased serum antibody titers against three previously characterized proteins, FNZ (cell surface-bound fibronectin binding protein), SFS (secreted fibronectin binding protein), and EAG (alpha2-macroglobulin, albumin, and immunoglobulin G [IgG] binding protein) from S. equi. To assess the protective efficacy of vaccination with these three proteins, a mouse model of equine strangles was utilized. Parts of the three recombinant proteins were used to immunize mice, either subcutaneously or intranasally, prior to nasal challenge with S. equi subsp. equi. The adjuvant used was EtxB, a recombinant form of the B subunit of Escherichia coli heat-labile enterotoxin. It was shown that nasal colonization of S. equi subsp. equi and weight loss due to infection were significantly reduced after vaccination compared with a mock-vaccinated control group. This effect was more pronounced after intranasal vaccination than after subcutaneous vaccination; nearly complete eradication of nasal colonization was obtained after intranasal vaccination (P < 0.001). When the same antigens were administered both intranasally and subcutaneously to healthy horses, significant mucosal IgA and serum IgG antibody responses against FNZ and EAG were obtained. The antibody response was enhanced when EtxB was used as an adjuvant. No adverse effects of the antigens or EtxB were observed. Thus, FNZ and EAG in conjunction with EtxB are promising candidates for an efficacious and safe vaccine against strangles.

Array of M Protein Gene Subtypes in 1064 Recent Invasive Group A Streptococcus Isolates Recovered from the Active Bacterial Core Surveillance

Using sequence analysis to detect variation within the hypervariable M protein N terminus, we found 41 emm types encompassing 81 subtypes, among 1064 consecutive invasive group A streptococcus isolates from a recent multistate, population-based surveillance. Seventeen of the 30 emm types represented by multiple isolates displayed multiple subtypes. Most subtypes differed from reference strain emm sequences as a result of single base substitutions or other alterations likely to be stably inherited. The Centers for Disease Control and Prevention database (available at: http://www.cdc.gov/ncidod/biotech/strep/strepblast.htm) currently contains 225 distinct emm types encompassing 450 subtypes. Although this subtyping scheme increases specificity, limited variation within individual types favors introduction of M protein type-specific vaccines.

[Construction of plant expression plasmid of chimera SBR-CT delta A1]

OBJECTIVE

The purpose of this study is to construct plant expression plasmid containing the gene encoding chimera SBR-CT delta A1.

METHODS

The target gene fragment P2, including the gene-encoded chimera SBR-CT delta A1 (3,498-5,378 bp), was obtained by standard PCR amplification. The PCR products were ligated with pGEM-easy vector through TA clone to form plasmid pTSC. The plasmid pTSC and plasmid pPOKII were digested by restricted endonuclease BamHI and KpnI, and the digested products were extracted and purified for recombination. Then the purified P2 and plasmid pPOKII were recombined by T4 DNA ligase to form recombinant plasmid pROSC; inserting bar gene into the plasmid and form pROSB plasmid. The recombined plasmids were isolated and identified by restricted endonuclease cutting and Sanger dideoxy DNA sequencing.

RESULTS

P2 gene was linked to pPOKII plasmid and formed recombinant plasmid pROSC. The DNA sequence and orientation were corrected. And bar gene was inserted into pPOSC and form recombinant plasmid pROSB.

CONCLUSION

Plant expression vector pROSC and pROSB containing the gene encoding chimera SBR-CT delta A1, which may provide useful experiment foundation for further study on edible vaccine against caries have been successfully constructed.

[Construction and expression of traceable DNA vaccine for prevention of caries]

OBJECTIVE

Streptococcus mutans has been proved as a causative bacteria of human dental caries. The surface protein antigen is one of the important pathogenic factors. The A region of the surface protein antigen pac gene (pacA) can enrich T-cells and B-cells epitope. In this study, a DNA vaccine carrying pacA and gfp gene (a reporter gene) for caries prevention was constructed. The DNA vaccine was liable to be traced in vitro and in vivo.

METHODS

The fragment of pacA (1.3 kb) was amplified by PCR with the plasmid pPC41 as template, and inserted into a pEGFP-C1 vector. The recombinant plasmid produced was named as pEGFPC1-pacA. After the COS1 cell line was transfected by the recombinant plasmid, the expression of gfp was detected by observing the green fluorescence and measuring the fluorescence intensity, and the expression of pacA was detected by RT-PCR.

RESULTS

Restricted analyzing, sequencing and PCR technique were employed to identify the recombinant plasmid. The phase and orientation of the pacA gene inserted into the vector pEGFPC1 were correct and no changes of their open reading frames were discovered. The transfected COS1 carrying green fluorescent protein (GFP) was observed; the GFP expression level of transfected cells was higher than that of controlled cell. The transcript of pacA gene was confirmed by RT-PCR.

CONCLUSION

Construction of the recombinant plasmid was successful. The gfp gene and pacA gene in the plasmid was transcribed and expressed simultaneously in the transfected cells. Moreover, detection of GFP is simple, safe and effective for living cells.

[Study on potential anti-caries DNA vaccine pcDNA3-gtfB integration into host cell genome]

OBJECTIVE

Gene vaccine security is of concern because of the possibility of insertion mutagenesis resulting in inactivation of tumor suppressor or activation of oncogene. The purpose of this study was to examine the potential of anti-caries DNA vaccine pcDNA3-gtfB integrating into the host cell genome.

METHODS

Anti-caries DNA vaccine pcDNA3-gtfB was constructed by the previous study. The gtfB gene(904-4,578 bp, genebank M17361) was cloned from Streptococcus mutans GS-5. 36 Wistar rats were divided into 2 groups: submandibular gland-targeted injection(SGT) group and control group. Rats in SGT group were injected with 100 micrograms of plasmid pcDNA3-gtfB, rats in control group with PBS solution. Genomes from submandibular gland, kidney, heart, liver, lung, and brain tissues were isolated later in 12 weeks. Genomes from different tissues were purified by low-melting agarose electrophoresis. Using the purified genomes as template, plasmid integration were examined by PCR(upper primer: 5'-ATATGGTACCATGACCGAAGCGACATCTAAGCAAGA-3', lower primer: 5'-ACTACTCGAGTTAGAACCATTGACCCTG AGCATTGC-3'). The sensitivity level of PCR was determined by adding gradient plasmid copies into genomes in control group.

RESULTS

The examination of 6 tissues failed in revealing any evidence of integration at the sensitivity level that could detect 1 copy integration in 10,000 nuclei.

CONCLUSION

The potential frequency of plasmid pcDNA3-gtfB integration into host cell genome would not exceed that of the spontaneous mutation. It was indicated that pcDNA3-gtfB was genetically safe as a promising anti-carious DNA vaccine.

[Construction and cellular expression of GTF-PAc fusion anti-caries DNA vaccine]

OBJECTIVE

To construct a fusion anti-caries DNA vaccine pGLUA-P carrying GLU fragment from gtfB gene of Streptococcus mutans GS-5 and A-P fragment including the A region and P region of PAc protein from a DNA anti-caries vaccine pCIA-P, and to investigate its expression in prokaryotic and eukaryotic cells.

METHODS

The sequence of GLU fragment in pGLU plasmid was testified by DNA sequencing. The fusion anti-caries DNA vaccine was constructed by ligating A-P fragment from pCIA-P to pGLU. The expression of GLUA-P fusion protein in E. coli BL21 (DE3) was induced by IPTG and checked by SDS-PAGE electrophoresis. pGLUA-P was transfected in vitro to cultured rat primary muscle cells by cation liposome Dosper, and immunohistochemical method was used to test the expression of GLUA-P fusion protein in cells.

RESULTS

GLU sequence was identical with relative sequence of GTF-I (GS-5 strain) in Gene Bank. Recombinant eukaryotic expression plasmid pGLUA-P was confirmed to have both GLU and A-P fragment. After pGLUA-P was transferred into E. coli (DE3), it could express a new 115 000 protein by the induce of IPTG. Specific brown products could be found in the cytoplasm of cultured rat primary muscle cells transfected by pGLUA-P.

CONCLUSIONS

Fusion anti-caries DNA vaccine pGLUA-P is successfully constructed and confirmed by sequencing and enzymes digestion. Fusion GLUA-P protein can be correctly expressed in prokaryotic and eukaryotic cells.

[Intranasal immunization against dental caries with plasmid DNA encoding pac gene of Streptococcus mutans in gnotobiotic rats]

OBJECTIVES

To assess the efficacy of plasmid DNA encoding pac gene of Streptococcus mutans (S. mutans) intranasally immunized in gnotobiotic rats and to compare the effect of two different delivery systems.

METHODS

Sprague Dawley rats, infected with S. mutans at 20 days of age, were intranasally immunized with plasmid pCIA-P (group A), Dosper-DNA complex (group B), Bupivacaine-DNA complex (group C). Control rats were either immunized with plasmid pCI (group D), distilled water (group E) or immunized intramuscularly (group F). All the rats were boosted 2 weeks later. ELISA determined the antibodies against the vaccines. Keyes caries score was used to evaluate the anti- caries effectiveness of the vaccines at the terminal study.

RESULTS

As for the antibody reactions, there were significantly (P < 0.01) differences between rats immunized with DNA vaccine and non-immunized rats. And rats in group B and C had the significantly (P < 0.01) higher level of specific salivary anti-PAc IgA antibodies and rats (group B, C, F) had the significantly (P < 0.01) higher specific serum anti-PAc IgG responses to DNA vaccine. Keyes scores of rats (group B and C) were significantly (P < 0.01) lower than others.

CONCLUSIONS

Intranasal immunization with plasmid pCIA-P encoding pac gene successfully reduces the caries and appears to be a promising approach against dental caries. Cationic liposome Dosper and local anesthetic bupivacaine could enhance the efficacy of DNA vaccine.

Biological consequences of antigen and cytokine co-expression by recombinant Streptococcus gordonii vaccine vectors

To test the effect of co-expression of immunomodulatory molecules, together with target antigen, two recombinant Streptococcus gordonii strains were constructed which secreted either murine interleukin-2 (IL-2) or interferon-gamma (IFN-gamma) in addition to a surface anchored test antigen (the conserved C-repeat region (CRR) of the M6 protein of Streptococcus pyogenes). The secretion of functional cytokines by S. gordonii was achieved by in-frame fusion of sequences encoding mature IL-2 or IFN-gamma to the sequences encoding the leader signal of the M6 protein. Expression of the M protein CRR region from a separate chromosomal site produced double recombinants expressing a secreted cytokine and the M protein CRR region anchored to the surface. Protein expression was verified by streak blot, immunoblot, and ELISA on both the single and double recombinants. A cytokine bioassay using HT-2 cells verified biological activity of recombinant IL-2 secreted from S. gordonii. When mice were immunized subcutaneously with the different S. gordonii expression strains, cytokine co-expression apparently modulated the systemic immune response. These results show that streptococci can deliver biologically active molecules such as cytokines along with antigens to the immune system. These results demonstrate that a cytokine-secreting, noninvasive, bacterial vaccine vector can be used to modulate immune responses to a co-expressed antigen.

Immunisation of dairy cattle with recombinant Streptococcus uberis GapC or a chimeric CAMP antigen confers protection against heterologous bacterial challenge

The gapC genes, encoding the cell surface-associated GapC proteins of S. uberis and S. agalactiae, have been cloned and sequenced. To identify potential vaccine candidates against S. uberis-induced bovine mastitis, lactating dairy cows were vaccinated with either (6 x His)GapC of S. uberis or S. dysgalactiae, or with a chimeric CAMP-factor antigen, CAMP-3. For 7 days following heterologous challenge with S. uberis, milk somatic cell counts were determined to assess differences in the severity of mastitis between vaccinates and an unvaccinated control group. Vaccination with S. uberis (6 x His)GapC or CAMP-3 resulted in a significant reduction in inflammation on several days post-challenge, most significantly for the former antigen. Inflammation was not reduced in S. dysgalactiae (6 x His)GapC vaccinates, suggesting that it does not confer cross-species protection.

Nasal mucosal immunogenicity for the horse of a SeM peptide of Streptococcus equi genetically coupled to cholera toxin

The intranasal immunogenicity of cholera toxin (CT) genetically coupled to peptide sequence aa236-334 (F3) of the SeM protein of Streptococcus equi was studied in five young adult Welsh ponies. All ponies made rapid CTB- and SeMF3-specific serum antibody responses following the first immunization. Specific nasal IgA responses were detected in two ponies 14 days after the first immunization, in another two 14 days after a second immunization on day 14, and in all ponies 28 days after a third immunization on day 42. SeMF3-specific antibody responses in sera and nasal washes were dominated by IgGb and IgA, respectively, and remained elevated for at least 140 days. Strong serum IgGa and IgG(T) responses were also observed. These antibody responses were qualitatively similar to those induced during recovery from equine strangles. Antibody responses in mucosal secretions were boosted in some ponies by immunizations subsequent to the first immunization, but antibodies in serum were never boosted. In vitro survival of S. equi was significantly reduced by SeMF3-specific antibodies in sera obtained 14 days after the second immunization but survival increased in sera collected following subsequent immunizations, possibly due to absence of synthesis of high affinity antibodies. Finally, the susceptibility of all immunized ponies to commingling challenge by S. equi indicated either that SeMF3 lacks protective epitopes or that the antibodies induced by the chimera were not at effective levels.

Expression of Streptococcus mutans wall-associated protein A gene in Chinese hamster ovary cells: prospect for a dental caries DNA vaccine

The Streptococcus mutans strain GS-5 wall-associated protein A (Wap-A) is a precursor to the extracellular antigen A (AgA), a recognized candidate dental caries vaccine. The full-length wapA gene (wapA-E) and a C-terminal truncated version (wapA-G) encoding the AgA were cloned into the mammalian expression vector pcDNA 3.1/V5/His-TOPO. The resulting constructs were propagated in the Escherichia coli Top10. To investigate the expression of the S. mutans genes in mammalian cells, the above constructs were used to transfect Chinese hamster ovary (CHO) cells in the presence of the cationic lipid pfx-8. Transient expression of the wapA-E and wapA-G genes was observed at 24 h post-transfection, as shown by Western immunoblot analysis using a rabbit antiserum to S. mutans cell wall. Immunochemical staining of the transfected CHO cells showed expression of WapA mainly in the cells and budding vesicles, whereas AgA was found mainly in the transfected cells and extracellular medium. The expression of S. mutans proteins in CHO cells, in either vesicles or soluble form, suggested an antibody response to the above DNA constructs. Work is under way to test the efficacy of these as DNA vaccines against S. mutans.