Importance of subunit vaccine antigen of major Fli C antigenic site of Salmonella enteritidis II: a challenge trial

Identification and Evaluation of Novel Antigen Candidates against Salmonella Pullorum Infection Using Reverse Vaccinology

Pullorum disease, caused by the Salmonella enterica serovar Gallinarum biovar Pullorum, is a highly contagious disease in the poultry industry, leading to significant economic losses in many developing countries. Due to the emergence of multidrug-resistant (MDR) strains, immediate attention is required to prevent their endemics and global spreading. To mitigate the prevalence of MDR Salmonella Pullorum infections in poultry farms, it is urgent to develop effective vaccines. Reverse vaccinology (RV) is a promising approach using expressed genomic sequences to find new vaccine targets. The present study used the RV approach to identify new antigen candidates against Pullorum disease. Initial epidemiological investigation and virulent assays were conducted to select strain R51 for presentative and general importance. An additional complete genome sequence (4.7 Mb) for R51 was resolved using the Pacbio RS II platform. The proteome of Salmonella Pullorum was analyzed to predict outer membrane and extracellular proteins, and was further selected for evaluating transmembrane domains, protein prevalence, antigenicity, and solubility. Twenty-two high-scored proteins were identified among 4713 proteins, with 18 recombinant proteins successfully expressed and purified. The chick embryo model was used to assess protection efficacy, in which vaccine candidates were injected into 18-day-old chick embryos for in vivo immunogenicity and protective effects. The results showed that the PstS, SinH, LpfB, and SthB vaccine candidates were able to elicit a significant immune response. Particularly, PstS confers a significant protective effect, with a 75% survival rate compared to 31.25% for the PBS control group, confirming that identified antigens can be promising targets against Salmonella Pullorum infection. Thus, we offer RV to discover novel effective antigens in an important veterinary infectious agent with high priority.

Salmonella Enteritidis Subunit Vaccine Candidate Based on SseB Protein Co-Delivered with Simvastatin as Adjuvant

Salmonella enterica serovar Enteritidis (S. Enteritidis) is an important zoonotic pathogen that can lead to diarrhea and systemic infections in humans and mortality in animals. This is a major public health issue worldwide. Safe and effective vaccines are urgently needed to control and prevent Salmonella infection. Subunit vaccines are safe and provide targeted protection against Salmonella spp. Here, we developed and evaluated an S. Enteritidis subunit vaccine candidate, the rHis-SseB adjuvant with simvastatin. We amplified the SseB gene from S. Enteritidis C50041 genomic DNA and expressed the recombinant proteins rHis-SseB and rGST-SseB using the Escherichia coli system. Western blotting confirmed the immunoreactivity of recombinant proteins rHis-SseB and rGST-SseB with antisera against Salmonella Enteritidis C50041. In a mouse model of intramuscular vaccination, co-immunization with rHis-SseB and simvastatin significantly enhanced both the SseB-specific antibody titer in serum (humoral immune response) and splenic lymphocyte proliferation (cellular immune response). Co-immunization with rHis-SseB and simvastatin provided 60% protection against subsequent challenge with the S. Enteritidis C50041 strain and decreased bacterial colonization in the liver and spleen. These findings provide a basis for the development of an S. Enteritidis subunit vaccine.

Efficacy of Multivalent, Cochleate-Based Vaccine against Salmonella Infantis, S. Enteritidis and S. Typhimurium in Laying Hens

Salmonella enterica is an important foodborne pathogen. Commercial poultry are the main reservoirs of Salmonella enterica, leading to the contamination of food and outbreaks in humans. The vaccination of chickens is one of the most important strategies to reduce the number of Salmonella in poultry farms. Unfortunately, commercial vaccines have not been fully effective in controlling the spread and do not contain all the Salmonella serovars that circulate on farms. In this study, we evaluate a new, cochleate-based, trivalent injectable vaccine against S. Enteritidis, S. Typhimurium and S. Infantis, describing the vaccine security, capacity to induce specific anti-Salmonella serovar IgY and the gene expression of immune markers related to CD4 and CD8 T-cell-mediated immunity. Efficacy was evaluated through oral challenges performed separately for each Salmonella serotype. The efficacy and safety of the trivalent vaccine was proven under controlled conditions. The vaccine has no local or systemic reactions or adverse effects on poultry performance related to the vaccine. The vaccine provided significantly increased serum IgY titer levels, significantly reduced Salmonella CFU/g present in the cecum and an increased CD4+/CD8+ ratio in vaccinated animals when challenged with S. Infantis, S. Enteritidis and S. Typhimurium. These results indicate that this new trivalent vaccine does not generate adverse effects in poultry and produces an increase in neutralizing antibodies against the three Salmonella serovars.

Reduction in intestinal colonization and invasion of internal organs after challenge by homologous and heterologous serovars of Salmonella enterica following vaccination of chickens with a novel trivalent inactivated Salmonella vaccine

A novel inactivated vaccine, comprising three serovars of Salmonella enterica (Enteritidis, serogroup O:9; Typhimurium, serogroup O:4; Infantis, serogroup O:7) grown under conditions of iron restriction and adjuvanted with aluminium hydroxide, was evaluated for efficacy following challenge by homologous and heterologous serovars. Chickens were vaccinated at 6 and 10 weeks of age by the intramuscular route and challenged 4 to 9 weeks after the second vaccination with serovars belonging to serogroup O:9 (Enteritidis), O:4 (Typhimurium and Heidelberg), O:7 (Infantis and Virchow), and O:8 (Hadar). All vaccinated birds produced a marked systemic antibody response against each of the component vaccine antigens by the time of challenge. Significant reductions in both colonization of the intestinal tract and invasion of internal organs were observed in vaccinated birds compared with non-vaccinated controls, irrespective of the challenge serovar. The findings suggest that broad serovar protection within the constitutive serogroups of an inactivated multi-valent vaccine is possible and could, therefore, play an important role in future Salmonella control programmes. RESEARCH HIGHLIGHTS Novel inactivated trivalent Salmonella chicken vaccine was developed and tested. Vaccine induced marked systemic antibody response against all vaccine antigens. Significant reductions in intestinal tract colonization and internal organ invasion. Vaccine efficacy demonstrated against homologous and heterologous serovars.

Potential Impact of Food Safety Vaccines on Health Care Costs

Foodborne pathogens continue to cause several outbreaks every year in many parts of the world. Among the bacterial pathogens involved, Shiga toxin-producing Escherichia coli, Campylobacter jejuni, and nontyphoidal Salmonella species cause a significant number of human infections worldwide, resulting in a huge annual economic burden that amounts to millions of dollars in health care costs. Human infections are primarily caused by the consumption of contaminated food. Vaccination of food-producing animals is an attractive, cost-effective strategy to lower the levels of these pathogens that will ultimately result in a safer food supply and fewer human infections. However, producers are often reluctant to routinely vaccinate animals against these pathogens since they do not cause any detectable clinical symptoms. This review highlights recent approaches used to develop effective food safety vaccines and the potential impact these vaccines might have on health care costs.

Salmonella vaccines in poultry: past, present and future

Salmonella species are important zoonotic pathogens that cause gastrointestinal disease in humans and animals. Poultry products contaminated with these pathogens are one of the major sources of human Salmonella infections. Vaccination of chickens, along with other intervention measures, is an important strategy that is currently being used to reduce the levels of Salmonella in poultry flocks, which will ultimately lead to lower rates of human Salmonella infections. However, despite numerous studies that have been performed, there is still a need for safer, well-defined Salmonella vaccines. This review examines the different classes of Salmonella vaccines that have been tested, highlighting the merits and problems of each, and provides an insight into the future of Salmonella vaccines and the platforms that can be used for delivery.

Immunological changes at point-of-lay increase susceptibility to Salmonella enterica Serovar enteritidis infection in vaccinated chickens

Chicken eggs are the main source of human Salmonella enterica serovar Enteritidis infection. S. Enteritidis infects the oviduct and ovary of the chicken leading to infection of developing eggs. Therefore, control in poultry production is a major public health priority. Vaccination of hens has proved successful in control strategies in United Kingdom leading to a 70% drop in human cases since introduced. However, as hens reach sexual maturity they become immunosuppressed and it has been postulated this leads to increased susceptibility to Salmonella infection. In this study we define the changes to the systemic and reproductive tract-associated immune system of hens throughout sexual development by flow cytometry and histology and determine changes in susceptibility to experimental S. Enteritidis challenge in naive and vaccinated hens. Changes to both systemic and local immune systems occur in chickens at sexual development around 140 days of age. The population of several leukocyte classes drop, with the greatest fall in CD4+ lymphocyte numbers. Within the developing reproductive tract there an organised structure of lymphocytic aggregates with γδ-T lymphocytes associated with the mucosa. At point-of-lay, this organised structure disappears and only scattered lymphocytes remain. Protection against Salmonella challenge is significantly reduced in vaccinated birds at point-of-lay, coinciding with the drop in CD4+ lymphocytes. Susceptibility to reproductive tract infection by Salmonella increased in vaccinated and naïve animals at 140 and 148 days of age. We hypothesise that the drop in γδ-T lymphocytes in the tract leads to decreased innate protection of the mucosa to infection. These findings indicate that systemic and local changes to the immune system increase the susceptibility of hens to S. Enteritidis infection. The loss of protective immunity in vaccinated birds demonstrates that Salmonella control should not rely on vaccination alone, but as part of an integrated control strategy including biosecurity and improved animal welfare.

Development and evaluation of gamma irradiated toxoid vaccine of Salmonella enterica var Typhimurium

Development of a single effective vaccine against non-typhoidal salmonellosis is very challenging due to the presence of hundreds of serovars of Salmonella which are antigenically different from each other. The Salmonella enterotoxin (Stn), a common virulence factor occurring amongst a wide range of serovars, used as a formalized toxoid vaccine has been found to be effective against homologous and heterologous serovars. However, the process of formalization has its own drawbacks. Gamma radiation (γ) on the other hand is widely used as a safe and convenient method of sterilization worldwide. In this experiment we used gamma rays to inactivate the partially purified Stn of Salmonella enterica serovar Typhimurium (DT 193). The toxoid obtained was tested for its immunogenicity and loss of toxicity and then used to formulate a gamma irradiated toxoid vaccine (ITST). The efficacy of the developed ITST was tested in Kuroiler, a Broiler breed, against homologous and heterologous challenges (S. Typhimurium and S. Gallinarum) administered intra-peritoneally and orally. Birds in groups challenged with S. Typhimurium by both routes recorded protective indices (PI) of 100% while birds in groups challenged intra-peritoneally with S. Gallinarum recorded PI of 83.33% and those challenged orally scored 100%. The overall protective index (PI) being 95.83%. The antibody titres calculated as geometric mean with standard error at 1:10(-4) dilutions showed a steep rise after the first dose and peaked at week 6 post primary vaccinations. Thus the ITST was found very effective in protecting poultry against both the challenge organisms tested.

Evaluation of recombinant Salmonella expressing the flagellar protein fliC for persistence and enhanced antibody response in commercial turkeys

Salmonella enterica serovar Enteritidis (SE) is one of the most common causes of human foodborne illness in the United States. Previous research indicates that antibodies against the fliC protein can provide protection against Salmonella challenge in mice. To generate a vaccine that effectively protects poultry against multiple Salmonella serotypes, novel attenuated strains of SE were developed to express a fliC peptide sequence on the outer membrane protein lamB in association with an M2e (marker) epitope. In 3 separate trials, poults were immunized with 10(7) to 10(8) cfu/poult of the appropriate recombinant Salmonella strains (ΔSE-M2e or ΔSE-M2e-fliC) via oral gavage on the day of hatch and again on d 21 posthatch. Liver, spleen, and cecal tonsils were aseptically removed on d 7, 14, 21, 28, 35, and 42 posthatch for detection of Salmonella, and blood samples were obtained at these same time points for determination of an M2e-specific antibody response. In all 3 trials, the ΔSE-M2e-fliC strain exhibited significantly less invasion of the liver and spleen at d 7 and 14 when compared with ΔSE-M2e or SE phage type 13A (P < 0.05). Similarly, colonization of the cecal tonsils was decreased in the poults immunized with the ΔSE-M2e-fliC strain. By d 21, the ΔSE-M2e-fliC strain exhibited a significantly higher M2e-specific antibody response when compared with the negative control and SE phage type 13A groups (P < 0.05). However, no significant differences in M2e-specific antibody responses were observed between the ΔSE candidate vaccine strains throughout the study. Overall, these data suggest that oral live attenuated Salmonella-vectored vaccines expressing a fliC peptide sequence are able to elicit a humoral immune response in commercial poults and may contribute to a reduction in Salmonella organ invasion and colonization.