Identification and characterization of a Streptococcus equi ssp. zooepidemicus immunogenic GroEL protein involved in biofilm formation.

Streptococcus equi ssp. zooepidemicus (S. equi spp. zooepidemicus) is an opportunistic pathogen that causes major economic losses in the swine industry in China and is also a threat for human health. Biofilm formation by this bacterium has been previously reported. In this study, we used an immunoproteomic approach to search for immunogenic proteins expressed by biofilm-grown S. equi spp. zooepidemicus. Seventeen immunoreactive proteins were found, of which nine common immunoreactive proteins were identified in planktonic and biofilm-grown bacteria. The immunogenicity and protective efficacy of the S. equi spp. zooepidemicus immunoreactive GroEL chaperone protein was further investigated in mice. The protein was expressed in vivo and elicited high antibody titers following S. equi spp. zooepidemicus infections of mice. An animal challenge experiment with S. equi spp. zooepidemicus showed that 75% of mice immunized with the GroEL protein were protected. Using in vitro biofilm inhibition assays, evidence was obtained that the chaperonin GroEL may represent a promising target for the prevention and treatment of persistent S. equi spp. zooepidemicus biofilm infections. In summary, our results suggest that the recombinant GroEL protein, which is involved in biofilm formation, may efficiently stimulate an immune response, which protects against S. equi spp. zooepidemicus infections. It may therefore be a candidate of interest to be included in vaccines against S. equi spp. zooepidemicus infections.

Recombinant Swinepox Virus for Veterinary Vaccine Development.

Poxvirus-vectors have been widely used in vaccine development for several important human and animal diseases; some of these vaccines have been licensed and used extensively. Swinepox virus (SPV) is well suited to develop recombinant vaccines because of its large packaging capacity for recombinant DNA, its host range specificity, and its ability to induce appropriate immune responses.

A novel vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection.

To develop a vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection, the genes of porcine IL-18, capsid protein (Cap) of PCV2 and M-like protein (SzP) of SEZ were inserted into the swinepox virus (SPV) genome by homologous recombination. The recombinant swinepox virus rSPV-ICS was verified by PCR and indirect immunofluorescence assays. To evaluate the immunogenicity of rSPV-ICS, 28 PCV2 and SEZ seronegative Bama minipigs were immunized with rSPV-ICS (n=8), commercial PCV2 vaccine and SEZ vaccine (n=8) or wild type SPV (n=8). The results showed that SzP-specific antibody and PCV2 neutralizing antibody of the rSPV-ICS immunized group increased significantly compared to the wild type SPV treated group after vaccination and increased continuously over time. The levels of IL-4 and IFN-γ in the rSPV-ICS immunized group were significantly higher than the other three groups, respectively. After been co-challenged with PCV2 and SEZ, 87.5% piglets in rSPV-ICS immunized group were survived. Significant reductions in gross lung lesion score, histopathological lung lesion score, and lymph node lesion score were noticed in the rSPV-ICS immunized group compared with the wtSPV treated group. The results suggested that the recombinant rSPV-ICS provided piglets with significant protection against PCV2-SEZ co-infection; thus, it offers proof-of-principle for the development of a vaccine for the prevention of these swine diseases.

Development of an Aeromonas hydrophila recombinant extracellular protease vaccine.

Aeromonas hydrophila (Ah) exists widely in the aquatic environment and infects a variety of animals. Extracellular protease (EPR) is an important protective antigen that induces a specific antibody response to resist Ah infection. In this study, two genes encoding extracellular protease epr2 and epr3 were linked within the expression vector pET32a to construct a recombinant pET-epr2-3 plasmid. The immunogenicity of the fusion protein epr2-3 was investigated as a subunit vaccine in ICR mice. The recombinant epr2-3 protein induced the production of high antibody titers. The survival rate against homogenous Ah J-1 challenge was significantly higher in the epr2-3 vaccinated group (≥80%) compared with the inactivated Ah vaccinated group and the challenge control group (P < 0.01), thus indicating that the recombinant epr2-3 protein provided significant protection against Ah infection. Therefore, the recombinant epr2-3 is a promising candidate for development as a vaccine against Ah infections.

Construction and immunogenicity of recombinant swinepox virus expressing capsid protein of PCV2.

To explore development of a vaccine against PCV2 infections, the gene of capsid protein (Cap) was inserted into the swinepox virus (SPV) genome by homologous recombination. The recombinant swinepox virus expressing capsid protein (rSPV-cap) was verified by PCR, western blot and immunofluorescence assays. To evaluate the immunogenicity of rSPV-cap, twenty-four PCV2 seronegative minipigs were immunized with rSPV-cap, wild type SPV (wtSPV; negative control), or PBS (challenge control). After inoculation with PCV2, pigs in the rSPV-cap immunized group showed significantly higher average daily weight gain (ADG) and shorter fever duration compared with the wtSPV treated group (P<0.05). Cap-specific antibody in the rSPV-cap immunized group increased dramatically after vaccination and increased continuously over time. PCV2 genomic copies in the serum of rSPV-cap immunized pigs were significantly less compared with the wtSPV treated group at all time points after inoculation (P<0.01). Significant reduction in gross lung lesion scores, histopathological lung lesion scores, and lymph node lesion scores were noted in the rSPV-cap immunized group compared with the wtSPV treated group (P<0.01). The results suggested that the recombinant rSPV-cap provided pigs with significant protection from PCV2-associated disease; thus, it offers proof-of-principle for the development of a vaccine for the prevention of PCV2-associated disease in pigs.

A novel vaccine against Streptococcus equi ssp. zooepidemicus infections: the recombinant swinepox virus expressing M-like protein.

To develop a safer, more immunogenic and efficacious vaccine against Streptococcus equi ssp. zooepidemicus (SEZ) infections, the gene of M-like protein (SzP) was placed under the strong vaccinia virus promoter P28 and then inserted into swinepox virus (SPV) genome. The recombinant swinepox virus (rSPV-szp) was isolated in a non-selective medium by the co-expression of Escherichia coli LacZ gene and verified by PCR, western blotting and immunofluorescence assays. To evaluate the immunogenicity of this rSPV-szp, ICR mice were immunized with the rSPV-szp, inactivated SEZ vaccine (positive control), wild type SPV (negative control), or PBS (challenge control). All mice were intraperitoneally challenged with 5 LD(50) of homogenous ATCC 35246 strain 14 days post-vaccination. The results showed that at least 70% mice in rSPV-szp-vaccinated group were protected against homogenous ATCC 35246 challenge, the survival rate was significantly higher compared with mice in the negative control group and the challenge control group (P<0.001). The antibody titers of the rSPV-szp-vaccinated group were significantly higher (P<0.05) than the other three groups. Passive immune protection assays showed that the hyperimmune sera against M-like protein could provide mice with complete protection against challenge of ATCC 35246. Semi-quantitative RT-PCR analysis showed a marked increased in levels of IL-4 and IFN-γ mRNA in immunized mice. The results suggested that the recombinant rSPV-szp provided mice with significant protection from the SEZ infections. It is a promising candidate for the vaccine development against SEZ infections.