Construction of a Salmonella Gallinarum ghost as a novel inactivated vaccine candidate and its protective efficacy against fowl typhoid in chickens

Abstract

In order to develop a novel, safe and immunogenic fowl typhoid (FT) vaccine candidate, a Salmonella Gallinarum ghost with controlled expression of the bacteriophage PhiX174 lysis gene E was constructed using pMMP99 plasmid in this study. The formation of the Salmonella Gallinarum ghost with tunnel formation and loss of cytoplasmic contents was observed by scanning electron microscopy and transmission electron microscopy. No viable cells were detectable 24 h after the induction of gene E expression by an increase in temperature from 37 °C to 42 °C. The safety and protective efficacy of the Salmonella Gallinarum ghost vaccine was tested in chickens that were divided into four groups: group A (non-immunized control), group B (orally immunized), group C (subcutaneously immunized) and group D (intramuscularly immunized). The birds were immunized at day 7 of age. None of the immunized animals showed any adverse reactions such as abnormal behavior, mortality, or signs of FT such as anorexia, depression, or diarrhea. These birds were subsequently challenged with a virulent Salmonella Gallinarum strain at 3 weeks post-immunization (wpi). Significant protection against the virulent challenge was observed in all immunized groups based on mortality and post-mortem lesions compared to the non-immunized control group. In addition, immunization with the Salmonella Gallinarum ghosts induced significantly high systemic IgG response in all immunized groups. Among the groups, orally-vaccinated group B showed significantly higher levels of secreted IgA. A potent antigen-specific lymphocyte activation response along with significantly increased percentages of CD4+ and CD8+ T lymphocytes found in all immunized groups clearly indicate the induction of cellular immune responses. Overall, these findings suggest that the newly constructed Salmonella Gallinarum ghost appears to be a safe, highly immunogenic, and efficient non-living bacterial vaccine candidate that protects against FT.

Preparation and Evaluation of Chemically Inactivated Salmonella Enteritidis Vaccine in Chickens

“…It should be noted that the new strategy for NaOH-induced BGs was fast [13]. Moreover, other researchers [17] have shown the lysis efficiency of genetically inactivated BGs after lysis was 99.9%.…”

“…The resultant BGs share their functional and antigenic determinants of the envelope and represent an excellent vaccine candidate [12]. BGs from pathogenic bacteria were reported to be controlled and can protect against infectious diseases [13]. The mucosal immunizations with Escherichia coli ghosts were reported to induce protective immunity in an SPF chicken model [14].…”

Characterization of aSalmonellaTyphimurium ghost carrying an adjuvant protein as a vaccine candidate for the protection of chickens against virulent challenge

“…As bacterial ghosts retain all of the surface immunogenic determinants of their living counterparts, they are capable of stimulating strong immune responses, and their vaccine potential has been demonstrated experimentally for the prevention of pathogenic Gram-negative bacterial infections of veterinary importance Marchart et al, 2003;Chaudhari et al, 2012;Jawale et al, 2012;Hu et al, 2013). Here, we used Salmonella Typhimurium ghosts carrying LTB for vaccination experiments in the chicken model.…”

“…Vaccination trials in the laboratory or food-producing animals have demonstrated the ability of bacterial ghost vaccines to stimulate strong induction of immune responses accompanied by significant protection against virulent challenge (Wang & Lu, 2009;Chaudhari et al, 2012;Jawale et al, 2012;Hu et al, 2013). In our experiments, we employed only a fixed time window for challenge and reisolation of the bacteria, and a high dose of virulent challenge strain was used.…”

“…Bacterial ghosts are generated by the controlled expression of the plasmid-encoded PhiX174 lysis gene E encoding the 91-amino-acid residue hydrophobic protein E. The induction of protein E-mediated lysis leads to the formation of transmembrane tunnel structures by fusing the inner and outer membranes of Gram-negative bacteria, which consequently leads to a loss of cytoplasmic contents (Witte et al, 1992). To date, several studies have demonstrated that bacterial ghosts generated from pathogenic bacteria are capable of protecting against fatal Gram-negative infections Jalava et al, 2002;Marchart et al, 2003;Chaudhari et al, 2012;Jawale et al, 2012;Hu et al, 2013). Since the natural conformation of outer membrane proteins present in bacteria, including fimbriae, lipopolysaccharide, and peptidoglycan structures, is not altered during the production of bacterial ghosts, these empty bacterial envelopes possess high immunogenicity (Jalava et al, 2002).…”