Safety of bivalent live attenuated Salmonella vaccine and its protection against bacterial shedding and tissue invasion in layers challenged with Salmonella

A live attenuated Salmonella Typhimurium vaccine dose and diluent have minimal effects on the caecal microbiota of layer chickens

Among the Salmonella reduction strategies in poultry production, one option is to use a Salmonella vaccine. The aim of vaccinating layer flocks is to reduce the shedding of wild-type Salmonella in the poultry environment, thereby reducing the contamination of poultry products (eggs and meat). Nutritive diluent and a higher dose of vaccine may enhance its colonization potential in the gut of chickens. In this study, a commercially available live attenuated vaccine (Vaxsafe® ST) was reconstituted in different media and delivered orally to day-old chicks at three different doses (107, 108, and 109 CFU/chick). Gut colonization of the vaccine strain and the effects of vaccination on gut microbiota were assessed in commercial-layer chickens. The vaccine diluent and dosage minimally affected microbiota alpha diversity. Microbiota beta diversity was significantly different (P < 0.05) based on the vaccine diluent and dose, which indicated that the vaccinated and unvaccinated chickens had different gut microbial communities. Differences were noted in the abundance of several genera, including Blautia, Colidextribacter, Dickeya, Enterococcus, Lactobacillus, Pediococcus, and Sellimonas. The abundance of Colidextribacter was significantly lower in chickens that received vaccine reconstituted in Marek's and water diluents, while Lactobacillus abundance was significantly lower in the water group. The highest vaccine dose (109 CFU/chick) did not significantly alter (P > 0.05) the abundance of microbial genera. Chicken age affected the microbiota composition more significantly than the vaccine dose and diluent. The abundance of Lactobacillus, Blautia, Caproiciproducens, Pediococcus, and Colidextribacter was significantly higher on day 14 compared with day 7 post-vaccination. The Salmonella Typhimurium vaccine load in the caeca was not significantly affected by diluent and vaccine dose; however, it was significantly lower (P < 0.0001) on day 14 compared with day 7 post-vaccination. Overall, the S. Typhimurium vaccine minimally affected the gut microbiota structure of layer chicks, whereas changes in microbiota were more significant with chicken age.

Prokaryotic and eukaryotic dual-expression plasmid-mediated delivery of Campylobacter jejuni antigens by live-attenuated Salmonella: A strategy for concurrent Th1 and Th2 immune activation and protection in chickens

Salmonella and Campylobacter are food-borne pathogens that significantly affect poultry production and are transmitted to humans. Long-term protection against these pathogens in chicken relies on a balanced Th1 and Th2 response. C. jejuni antigens were screened and a fusion antigen, including CadF + FlaA adhesin and flagellin antigenic fragments was developed and safely delivered by low-endotoxicity S. Typhimurium through pJHL270, a dual-expression plasmid featuring prokaryotic (Ptrc) and eukaryotic (CMV) promoters. Antigen expression in Salmonella and host cells was confirmed by western blotting and IFA. The vaccine construct JOL2999, triggered significant increases in IgY, IgA antibodies, CD4+ and CD8+ T cells, indicating humoral, mucosal, and cell-mediated responses against both pathogens. Elevations in pro-inflammatory cytokines TNFα, INF-γ, IL-2, and IL-4 and MHC I and II cell populations further suggest simultaneous Th1 and Th2 immune activation. Reduced pathogen load and histopathological inflammatory signs in vital organs upon challenge confirmed the protective efficacy in chickens.

Differential cytokine profiling and microbial species involved in cecal microbiota modulations in SPF chicks immunized with a dual vaccine against Salmonella Typhimurium infection

Salmonella Typhimurium (ST) infection in laying hens is a significant threat to public health and food safety. Host resistance against enteric pathogen invasion primarily relies on immunity and gut barrier integrity. This study applied the ST infection model and a dual live vaccine containing Salmonella Enteritidis (SE) strain Sm24/Rif12/Ssq and ST strain Nal2/Rif9/Rtt to investigate the cellular cytokine expression profiles and the differential community structure in the cecal microbiota of specific-pathogen-free (SPF) chicks and field-raised layers. The results showed that ST challenge significantly upregulated expressions of IL-1β in SPF chicks. Vaccination, on the other hand, led to an elevation in IFNγ expression and restrained IL-1β levels. In the group where vaccination preceded the ST challenge (S.STvc), heightened expressions of IL-1β, IL-6, IL-10, and IL-12β were observed, indicating active involvement of both humoral and cell-mediated immunity in the defense against ST. Regarding the cecal microbiota, the vaccine did not affect alpha diversity nor induce a significant shift in the microbial community. Conversely, ST infection significantly affected the alpha and beta diversity in the cecal microbiota, reducing beneficial commensal genera, such as Blautia and Subdoligranulum. MetagenomeSeq analysis reveals a significant increase in the relative abundance of Faecalibacterium prausnitzii in the groups (S.STvc and STvc) exhibiting protection against ST infection. LEfSe further demonstrated Faecalibacterium prausnitzii as the prominent biomarker within the cecal microbiota of SPF chicks and field layers demonstrating protection. Another biomarker identified in the S.STvc group, Eubacterium coprostanoligenes, displayed an antagonistic relationship with Faecalibacterium prausnitzii, suggesting the limited biological significance of the former in reducing cloacal shedding and tissue invasion. In conclusion, the application of AviPro Salmonella DUO vaccine stimulates host immunity and modulates cecal microbiota to defend against ST infection. Among the microbial modulations observed in SPF chicks and field layers with protection, Faecalibacterium prausnitzii emerges as a significant species in the ceca. Further research is warranted to elucidate its role in protecting layers against ST infection.

Salmonella Infection in Poultry: A Review on the Pathogen and Control Strategies

Salmonella is the leading cause of food-borne zoonotic disease worldwide. Non-typhoidal Salmonella serotypes are the primary etiological agents associated with salmonellosis in poultry. Contaminated poultry eggs and meat products are the major sources of human Salmonella infection. Horizontal and vertical transmission are the primary routes of infection in chickens. The principal virulence genes linked to Salmonella pathogenesis in poultry are located in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2). Cell-mediated and humoral immune responses are involved in the defense against Salmonella invasion in poultry. Vaccination of chickens and supplementation of feed additives like prebiotics, probiotics, postbiotics, synbiotics, and bacteriophages are currently being used to mitigate the Salmonella load in poultry. Despite the existence of various control measures, there is still a need for a broad, safe, and well-defined strategy that can confer long-term protection from Salmonella in poultry flocks. This review examines the current knowledge on the etiology, transmission, cell wall structure, nomenclature, pathogenesis, immune response, and efficacy of preventative approaches to Salmonella.

Prevention and Control of Human Salmonella enterica Infections: An Implication in Food Safety

Salmonella is a foodborne zoonotic pathogen causing diarrhoeal disease to humans after consuming contaminated water, animal, and plant products. The bacterium is the third leading cause of human death among diarrhoeal diseases worldwide. Therefore, human salmonellosis is of public health concern demanding integrated interventions against the causative agent, Salmonella enterica. The prevention of salmonellosis in humans is intricate due to several factors, including an immune-stable individual infected with S. enterica continuing to shed live bacteria without showing any clinical signs. Similarly, the asymptomatic Salmonella animals are the source of salmonellosis in humans after consuming contaminated food products. Furthermore, the contaminated products of plant and animal origin are a menace in food industries due to Salmonella biofilms, which enhance colonization, persistence, and survival of bacteria on equipment. The contaminated food products resulting from bacteria on equipment offset the economic competition of food industries and partner institutions in international business. The most worldwide prevalent broad-range Salmonella serovars affecting humans are Salmonella Typhimurium and Salmonella Enteritidis, and poultry products, among others, are the primary source of infection. The broader range of Salmonella serovars creates concern over multiple strategies for preventing and controlling Salmonella contamination in foods to enhance food safety for humans. Among the strategies for preventing and controlling Salmonella spread in animal and plant products include biosecurity measures, isolation and quarantine, epidemiological surveillance, farming systems, herbs and spices, and vaccination. Other measures are the application of phages, probiotics, prebiotics, and nanoparticles reduced and capped with antimicrobial agents. Therefore, Salmonella-free products, such as beef, pork, poultry meat, eggs, milk, and plant foods, such as vegetables and fruits, will prevent humans from Salmonella infection. This review explains Salmonella infection in humans caused by consuming contaminated foods and the interventions against Salmonella contamination in foods to enhance food safety and quality for humans.

A Comprehensive Review on Bacterial Vaccines Combating Antimicrobial Resistance in Poultry

Bacterial vaccines have become a crucial tool in combating antimicrobial resistance (AMR) in poultry. The overuse and misuse of antibiotics in poultry farming have led to the development of AMR, which is a growing public health concern. Bacterial vaccines are alternative methods for controlling bacterial diseases in poultry, reducing the need for antibiotics and improving animal welfare. These vaccines come in different forms including live attenuated, killed, and recombinant vaccines, and they work by stimulating the immune system to produce a specific response to the target bacteria. There are many advantages to using bacterial vaccines in poultry, including reduced use of antibiotics, improved animal welfare, and increased profitability. However, there are also limitations such as vaccine efficacy and availability. The use of bacterial vaccines in poultry is regulated by various governmental bodies and there are economic considerations to be taken into account, including costs and return on investment. The future prospects for bacterial vaccines in poultry are promising, with advancements in genetic engineering and vaccine formulation, and they have the potential to improve the sustainability of the poultry industry. In conclusion, bacterial vaccines are essential in combating AMR in poultry and represent a crucial step towards a more sustainable and responsible approach to poultry farming.

Cytokines and cecal microbiome modulations conferred by a dual vaccine in Salmonella-infected layers

Zoonotic Salmonella infection is a critical and challenging issue for public health. Since human infections are mainly associated with consuming contaminated chicken products, strategies to reduce Salmonella carriage and shedding are essential. Here we investigate the mechanisms of the live attenuated Salmonella vaccine (AviPro Salmonella Duo) against Salmonella Enteritidis (SE) infection. We focused on inflammatory-related cytokine expressions and cecal microbiota modulations in specific-pathogen-free (SPF) and field layers. Forty-eight 2-day-old SPF layers were randomly allotted into S.SEvc, S.SEc, S.Vc, and S.Ct groups in trial 1. The equal number of filed layers at 25 wk were allocated into SEvc, SEc, Vc, and Ct groups in trial 2. Each group contained 12 layers. Groups were further assigned for vaccination (S.Vc and Vc groups), SE challenge (S.SEc and SEc groups), vaccination and the following SE challenge (S.SEvc and SEvc groups), or the placebo treatment (S.Ct and Ct groups). Cecal tissues and contents of layers on day 14 post-SE-challenges were collected for cytokine mRNA expression and 16S rRNA metagenomic analyses. We found that SE challenges significantly upregulated expressions of IFNγ, IL-1β, IL-12β, and NFκB1A in SPF layers. The vaccine notably counteracted the levels of IFNα, IFNγ, and NFκB1A activated by SE attacks. The vaccination, SE challenge, and their combination did not significantly affect alpha diversities but promoted dissimilarities in microbial communities between groups. Eubacterium_coprostanoligenes and Faecalibacterium_prausnitzii were identified as contributory taxa in the cecal microbiota of SE-challenged and vaccinated SPF layers. A significantly higher abundance of Faecalibacterium_prausnitzii in the ceca further correlated with the vaccination conferred protection against SE infection. In contrast, Oscillibacter_valericigenes and Mediterraneibacter_glycyrrhizinilyticus were featured taxa in Salmonella-infected field layers. Megamonas_hypermegale and Megamonas_rupellensis were identified as featured taxa in vaccinated field layers compared to SE-infected layers. To conclude, applying a dual Salmonella vaccine in this study modulated expressions of inflammatory-related cytokines and the cecal microbiome in layers, contributing to protection against SE infection. The feature microbes are promising for developing predictive indices and as antibiotic alternatives added to feed to reduce the risk of Salmonella shedding and contamination.