Attenuated Salmonella Gallinarum secreting an Escherichia coli heat-labile enterotoxin B subunit protein as an adjuvant for oral vaccination against fowl typhoid

Safety and efficacy of 9R live attenuated vaccine against fowl typhoid in partridge's species

Fowl typhoid is a significant avian disease worldwide affecting mainly chickens, turkeys and other bird species, such as partridges. In Morocco, the disease causes a high mortality rate in farmed partridges. Vaccination of partridges is a priority to preserve the breed however; the vaccine has never been evaluated in this species. The study was conducted to assess safety and efficacy of a locally produced Salmonella 9R live vaccine in partridges. Groups of vaccinated partridges received the vaccine at 6 weeks of age, followed by a second injection 6 weeks after. The challenge test was performed at 14 weeks with Salmonella gallinarum MSG1 virulent strain. The challenge demonstrated 65 % protection in vaccinated challenged partridges, with a reduction in organ invasion compared to unvaccinated control birds, which exhibited 70,6 % mortality. The live attenuated 9R vaccine, could be safely used to reduce flock losses and contribute to the reduction of infection.

Recombinant adenovirus carrying a core neutralizing epitope of porcine epidemic diarrhea virus and heat-labile enterotoxin B of Escherichia coli as a mucosal vaccine

Porcine epidemic diarrhea virus (PEDV) targets the intestinal mucosa in pigs. To protect against PEDV invasion, a mucosal vaccine is utilized effectively. In this study, we generated a recombinant adenovirus vaccine encoding the heat-labile enterotoxin B (LTB) and the core neutralizing epitope (COE) of PEDV (rAd-LTB-COE). The fusion protein LTB-COE was successfully expressed by the recombinant adenovirus in HEK293 cells, and the immunogenicity of the vaccine candidate was assessed in BALB/c mice and piglets. Three intramuscular or oral vaccinations with rAd-LTB-COE at two-week intervals induced robust humoral and mucosal immune responses. Moreover, a cell-mediated immune response was promoted in immunized mice, and the neutralizing antibody inhibited both the vaccine strain and the emerging PEDV isolate. Immunization experiments in piglets revealed that rAd-LTB-COE was immunogenic and induced good immune responses in piglets. Further studies are required to evaluate the efficacy of rAd-LTB-COE against a highly virulent PEDV challenge.

Recombinant-attenuated Salmonella Pullorum strain expressing the hemagglutinin-neuraminidase protein of Newcastle disease virus (NDV) protects chickens against NDV and Salmonella Pullorum challenge

Newcastle disease virus (NDV) and Salmonella Pullorum have significant damaging effects on the poultry industry, but no previous vaccine can protect poultry effectively. In this study, a recombinant-attenuated S. Pullorum strain secreting the NDV hemagglutinin-neuraminidase (HN) protein, C79-13ΔcrpΔasd (pYA-HN), was constructed by using the suicide plasmid pREasd-mediated bacteria homologous recombination method to form a new bivalent vaccine candidate against Newcastle disease (ND) and S. Pullorum disease (PD). The effect of this vaccine candidate was compared with those of the NDV LaSota and C79-13ΔcrpΔasd (pYA) strains. The serum hemagglutination inhibition antibody titers, serum immunoglobulin G (IgG) antibodies, secretory IgA, and stimulation index in lymphocyte proliferation were increased significantly more (p < 0.01) in chickens inoculated with C79-13ΔcrpΔasd (pYA-HN) than with C79-13ΔcrpΔasd (pYA) but were not significantly increased compared with the chickens immunized with the LaSota live vaccine (p > 0.05). Moreover, the novel strain provides 60% and 80% protective efficacy against the NDV virulent strain F48E9 and the S. Pullorum virulent strain C79-13. In summary, in this study, a recombinant-attenuated S. Pullorum strain secreting NDV HN protein was constructed. The generation of the S. Pullorum C79-13ΔcrpΔasd (pYA-HN) strain provides a foundation for the development of an effective living-vector double vaccine against ND and PD.

Intracellular delivery of HA1 subunit antigen through attenuated Salmonella Gallinarum act as a bivalent vaccine against fowl typhoid and low pathogenic H5N3 virus

Introduction of novel inactivated oil-emulsion vaccines against different strains of prevailing and emerging low pathogenic avian influenza (LPAI) viruses is not an economically viable option for poultry. Engineering attenuated Salmonella Gallinarum (S. Gallinarum) vaccine delivering H5 LPAI antigens can be employed as a bivalent vaccine against fowl typhoid and LPAI viruses, while still offering economic viability and sero-surveillance capacity. In this study, we developed a JOL1814 bivalent vaccine candidate against LPAI virus infection and fowl typhoid by engineering the attenuated S. Gallinarum to deliver the globular head (HA1) domain of hemagglutinin protein from H5 LPAI virus through pMMP65 constitutive expression plasmid. The important feature of the developed JOL1814 was the delivery of the HA1 antigen to cytosol of peritoneal macrophages. Immunization of chickens with JOL1814 produced significant level of humoral, mucosal, cellular and IL-2, IL-4, IL-17 and IFN-γ cytokine immune response against H5 HA1 and S. Gallinarum antigens in the immunized chickens. Post-challenge, only the JOL1814 immunized chicken showed significantly faster clearance of H5N3 virus in oropharyngeal and cloacal swabs, and 90% survival rate against lethal challenge with a wild type S. Gallinarum. Furthermore, the JOL1814 immunized were differentiated from the H5N3 LPAI virus infected chickens by matrix (M2) gene-specific real-time PCR. In conclusion, the data from the present showed that the JOL1814 can be an effective bivalent vaccine candidate against H5N3 LPAI and fowl typhoid infection in poultry while still offering sero-surveillance property against H5 avian influenza virus.

A Live Salmonella Gallinarum Vaccine Candidate Secreting an Adjuvant Protein Confers Enhanced Safety and Protection Against Fowl Typhoid

Live attenuated vaccines are used for effective protection against fowl typhoid (FT) in domestic poultry. In this study, a lon/cpxR/asd deletion mutant of Salmonella Gallinarum expressing the B subunit of a heat labile toxin (LTB) from Escherichia coli, a known adjuvant, was cloned in a recombinant p15A ori plasmid, JOL1355, and evaluated as a vaccine candidate in chickens. The plasmid was shown to be stable inside the attenuated Salmonella Gallinarum cell after three successive generations. Moreover, from an environmental safety point of view, apart from day 1 the JOL1355 strain was not detected in feces through day 21 postinoculation. For the efficacy of JOL1355, a total of 100 chickens were equally divided into two groups. Group A (control) chickens were intramuscularly inoculated with phosphate-buffered saline at 4 and 8 wk of age. Group B chickens were primed and boosted via the intramuscular route with 200 μL of a bacterial suspension of JOL1355 containing 1 × 10(8) colony forming units. All the chickens in Group A and B were challenged at 3 wk postbooster by oral inoculation with a wild-type Salmonella Gallinarum strain, JOL420. The JOL1355-immunized group showed significant protection and survival against the virulent challenge compared to the nonimmunized group. In addition, Group B exhibited a significantly higher humoral immune response, and the chickens remained healthy without any symptoms of anorexia, diarrhea, or depression. Group B also exhibited a significantly lower mortality rate of 4% compared to the 46% of the control group, which can be attributed to higher immunogenicity and better protection. The Group B chickens had significantly lower lesion scores for affected organs, such as the liver and spleen, compared to those of the control chickens (P < 0.01). These findings suggest that JOL1355 is a promising candidate for a safe and highly immunogenic vaccine against FT.

Utilization of a Modified Phage E Protein Lysis System Accounts for Increased Biomass in Salmonella Gallinarum Ghosts

A major limiting issue of bacterial ghost technology involves the stable maintenance of Phix174 lysis gene E expression. Unwanted leaky expression of gene E in the absence of induction temperature results in reduced biomass production of host bacterium, consequently leading to the lower yield of bacterial ghost. To mitigate the leaky expression status of lysis gene E, we utilized a novel E-lysis system in which gene E is located between sense λpR promoter with a CI857 regulator and antisense ParaBAD promoter with the AraC regulator. In the presence of L-arabinose at 28 C, unwanted transcription of lysis gene E from λpR promoter is repressed by a simultaneous transcription event from ParaBAD promoter by means of anti-sense RNA-mediated inhibition. Tight repression of lysis gene E in the absence of induction temperature resulted in higher bacterial cell number in culture suspension and, consequently, higher production of Salmonella Gallinarum (SG) ghost biomass. The safety and protective efficacy of the SG ghost vaccine were further examined in chickens. All of the immunized chickens showed significantly higher mucosal and systemic antibody responses accompanied by a potent antigen-specific lymphocyte proliferative response. Vaccination of chickens with SG ghost preparation offered efficient protection against wild-type SG challenge.

Generation of a safe Salmonella Gallinarum vaccine candidate that secretes an adjuvant protein with immunogenicity and protective efficacy against fowl typhoid

We constructed a live, attenuated Salmonella Gallinarum (SG) that secretes heat-labile enterotoxin B subunit protein (LTB), and evaluated this strain as a new vaccine candidate by assessing its safety, immunogenicity and protective efficacy against fowl typhoid. An asd(+) p15A ori low-copy plasmid containing eltB encoding LTB was transformed into a ΔlonΔcpxRΔasd SG (JOL967) to construct the candidate, JOL1355. In Experiments 1 and 2, birds were orally immunized with JOL1355 at 4 weeks of age, while control birds were inoculated with sterile phosphate-buffered saline. In Experiment 2, the birds of both groups were orally challenged with a virulent SG at 8 weeks of age. In Experiment 1, examination for safety revealed that the immunized group did not show any bacterial counts of the vaccine candidate in the liver and spleen. Birds immunized with the vaccine candidate showed a significant increase in systemic IgG and mucosal secretory IgA levels in Experiment 2. In addition, the lymphocyte proliferation response and the numbers of CD3(+)CD4(+) and CD3(+)CD8(+) T cells were also significantly elevated in the immunized group, which indicated that the candidate also induced cellular immune responses. In the protection assay, efficient protection with only 16% mortality in the immunized group was observed against challenge compared with 76% mortality in the control group. These results indicate that the live, attenuated SG secreting LTB can be a safe vaccine candidate. In addition, it can induce humoral and cellular immune responses and can efficiently reduce mortality of birds exposed to fowl typhoid.

Oral immunization with an attenuated Salmonella Gallinarum mutant as a fowl typhoid vaccine with a live adjuvant strain secreting the B subunit of Escherichia coli heat-labile enterotoxin

BACKGROUND

The Salmonella Gallinarum (SG) lon/cpxR deletion mutant JOL916 was developed as a live vaccine candidate for fowl typhoid (FT), and a SG mutant secreting an Escherichia coli heat-labile enterotoxin B subunit (LTB), designated JOL1229, was recently constructed as an adjuvant strain for oral vaccination against FT. In this study, we evaluated the immunogenicity and protective properties of the SG mutant JOL916 and the LTB adjuvant strain JOL1229 in order to establish a prime and boost immunization strategy for each strain. In addition, we compared the increase in body weight, the immunogenicity, the egg production rates, and the bacteriological egg contamination of these strains with those of SG 9R, a widely used commercial vaccine.

RESULTS

Plasma IgG, intestinal secretory IgA (sIgA), and cell-mediated responses were significantly induced after a boost inoculation with a mixture of JOL916 and JOL1229, and significant reductions in the mortality of chickens challenged with a wild-type SG strain were observed in the immunized groups. There were no significant differences in increases in body weight, cell-mediated immune responses, or systemic IgG responses between our vaccine mixture and the SG 9R vaccine groups. However, there was a significant elevation in intestinal sIgA in chickens immunized with our mixture at 3 weeks post-prime-immunization and at 3 weeks post-boost-immunization, while sIgA levels in SG 9R-immunized chickens were not significantly elevated compared to the control. In addition, the SG strain was not detected in the eggs of chickens immunized with our mixture.

CONCLUSION

Our results suggest that immunization with the LTB-adjuvant strain JOL1229 can significantly increase the immune response, and provide efficient protection against FT with no side effects on body weight, egg production, or egg contamination.