Combination of competitive exclusion and immunisation with a live Salmonella vaccine in newly hatched chickens: Immunological and microbiological effects

Salmonella spp. in poultry production-A review of the role of interventions along the production continuum

Salmonella is a significant pathogen of human and animal health and poultry are one of the most common sources linked with foodborne illness worldwide. Global production of poultry meat and products has increased significantly over the last decade or more as a result of consumer demand and the changing demographics of the world's population, where poultry meat forms a greater part of the diet. In addition, the relatively fast growth rate of birds which is significantly higher than other meat species also plays a role in how poultry production has intensified. In an effort to meet the greater demand for poultry meat and products, modern poultry production and processing practices have changed and practices to target control and reduction of foodborne pathogens such as Salmonella have been implemented. These strategies are implemented along the continuum from parent and grandparent flocks to breeders, the farm and finished broilers to transport and processing and finally from retail to the consumer. This review focuses on common practices, interventions and strategies that have potential impact for the control of Salmonella along the poultry production continuum from farm to plate.

Evaluation of the Protective Immune Response Induced by an rfbG-Deficient Salmonella enterica Serovar Enteritidis Strain as a Live Attenuated DIVA (Differentiation of Infected and Vaccinated Animals) Vaccine in Chickens

Salmonella enterica serovar Enteritidis (S. Enteritidis), one of the zoonotic pathogens, not only results in significant financial losses for the global poultry industry but also has the potential to spread to humans through poultry and poultry products. Vaccination is an effective method to prevent Salmonella infections. In this study, we constructed a live attenuated DIVA (differentiation of infected and vaccinated animals) vaccine candidate, Z11ΔrfbG, and evaluated its protective effectiveness and DIVA potential in chickens. Compared to that of the virulent wild-type strain, the 50% lethal dose (LD₅₀) of the rfbG mutant strain increased 56-fold, confirming its attenuation. High serum levels of S. Enteritidis-specific IgG titers indicated that a significant humoral immune response was induced in the vaccinated group. After challenge, the nonvaccinated group showed serious clinical symptoms (diarrhea, depression, decreased appetite, ruffled feathers, and weight loss), pathological changes (white nodules in the liver and fatty lesions in liver cells), and death. In contrast, there were no clinical symptoms, pathological changes, or death in the 5 × 10⁶- and 5 × 10⁷-CFU-vaccinated groups. Z11ΔrfbG vaccination significantly reduced S. Enteritidis colonization in the spleen, liver, and cecum. In addition, the Z11ΔrfbG-vaccinated group exhibited a negative response to the serological test, whereas the virulent wild-type Z11 infection group was strongly positive for the serological test, showing a DIVA capability of Z11ΔrfbG vaccination. Overall, our findings demonstrate the viability of the rfbG mutant as a live attenuated chicken vaccine that can discriminate between animals that have been immunized and those that have been infected. IMPORTANCE S. Enteritidis is a highly adapted pathogen that causes significant economic losses in the poultry industry around the world. Vaccination is an effective method of controlling S. Enteritidis infections. Here, we demonstrated that S. Enteritidis Z11ΔrfbG has the potential to be a safe, immunogenic, and DIVA vaccine candidate for the control of Salmonella infections in chickens. Z11ΔrfbG not only provided effective protection in chickens but also distinguished between infected and vaccinated chickens by serological tests.

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.

Invasion inhibition effects and immunogenicity after vaccination of SPF chicks with a Salmonella Enteritidis live vaccine

Objective Meat and eggs from chickens infected with Salmonella Enteritidis, Salmonella Typhimurium and Salmonella Infantis are considered to be an important source of Salmonella infections for humans. In order to control Salmonella infections in chickens, basic biosecurity measures are taken in combination with inactivated or attenuated live vaccines. Apart from an adaptive immune response, some live vaccines also induce innate immune mechanisms that prevent or inhibit systemic invasion with homologous Salmonella serovars. It is unknown whether these invasion inhibition effects are also directed against heterologous Salmonella serovars. Furthermore, it is unclear whether the adaptive immune response after vaccination with a Salmonella Enteritidis phage type 4 live vaccine is also directed against other phage types of Salmonella Enteritidis and Typhimurium.

Material and methods Specific pathogen-free day-old chicks were vaccinated orally with a commercially available Salmonella Enteritidis live vaccine. To test the invasion inhibition effect, the animals were challenged orally with a labelled Salmonella Typhimurium or Salmonella Infantis strain 1 day after vaccination. To demonstrate the adaptive immune response against non-phage type 4  Salmonella Enteritidis strains and a monophasic Salmonella Typhimurium strain, the chickens were challenged with Salmonella Enteritidis strains of phage types 1, 8 and 21 and a monophasic Salmonella Typhimurium strain (Definitive Type 193). After challenge, the abundance of the challenge strain in liver and cecal tissue was enumerated and compared with a corresponding control group.

Results Findings showed that the live Salmonella Enteritidis vaccine inhibits systemic invasion after early infection with Salmonella Typhimurium and Salmonella Infantis. Furthermore, adaptive immunity against the tested non-phage type 4  Salmonella Enteritidis strains and the monophasic Salmonella Typhimurium strain was demonstrated.

Conclusion and clinical relevance The results of this study demonstrate that vaccination with the Salmonella Enteritidis phage type 4 live vaccine significantly inhibits the invasion of Salmonella Typhimurium and Infantis. Furthermore, an adaptive immune response was also detected against non-phage type 4  Salmonella Enteritidis strains and a monophasic Salmonella Typhimurium strain.

The changing microbiome of poultry meat; from farm to fridge

Chickens play host to a diverse community of microorganisms which constitute the microflora of the live bird. Factors such as diet, genetics and immune system activity affect this complex population within the bird, while external influences including weather and exposure to other animals alter the development of the microbiome. Bacteria from these settings including Campylobacter and Salmonella play an important role in the quality and safety of end-products from these birds. Further steps, including washing and chilling, within the production cycle aim to control the proliferation of these microbes as well as those which cause product spoilage. These steps impose specific selective pressures upon the microflora of the meat product. Within the next decade, it is forecast that poultry meat, particularly chicken will become the most consumed meat globally. However, as poultry meat is a frequently cited reservoir of zoonotic disease, understanding the development of its microflora is key to controlling the proliferation of important spoilage and pathogenic bacterial groups present on the bird. Whilst several excellent reviews exist detailing the microbiome of poultry during primary production, others focus on fate of important poultry pathogens such as Campylobacter and Salmonella spp. At farm and retail level, and yet others describe the evolution of spoilage microbes during spoilage. This review seeks to provide the poultry industry and research scientists unfamiliar with food technology process with a holistic overview of the key changes to the microflora of broiler chickens at each stage of the production and retail cycle.

Can a combination of vaccination, probiotic and organic acid treatment in layer hens protect against early life exposure to Salmonella Typhimurium and challenge at sexual maturity?

Day old layer chicks were challenged with Salmonella Typhimurium using a seeder bird technique. Treatment groups were untreated control, administration of a probiotic in drinking water weekly, vaccination by intramuscular injection of a live aro-A deletion mutant vaccine at 10 weeks of age (woa) followed by an oral dose at 16 woa, probiotic administration plus vaccination, vaccination plus the administration of an organic acid preparation in feed from 16 woa and a combination of probiotic, vaccine and organic acid. Faecal shedding was monitored by culture at 1, 2, 3, 4, 8, 12, 15, 17, 20, 21, 23 and 25 woa and in dust from settle plates by PCR at intervals from 8 woa. Birds from each group were separated at 17 and 18 woa and challenged orally with 10⁶ CFU of S. Typhimurium. Both untreated and probiotic groups shed Salmonella until 56 days. Salmonella was also detected in dust from 8 until 12 woa but little after this. After vaccination, from sexual maturity (18 woa) all groups except those that were vaccinated with and without probiotic re-excreted Salmonella. The probiotic alone was ineffective against this re-excretion and all groups receiving organic acids shed Salmonella. At 17 woa, unchallenged controls were fully susceptible to caecal colonization, however all other groups showed reduced susceptibility, including the untreated challenged group. However, at 18 woa (sexual maturity) only the groups that were vaccinated with or without probiotic showed reduced susceptibility to colonization. The organic acid treated groups (including the vaccinated group) did not show a difference to the untreated controls. S. Typhimurium demonstrated an ability to re-emerge at sexual maturity, similar to other serovars. The vaccine assisted in limiting the re-excretion at sexual maturity and decreased susceptibility to subsequent challenge. Use of a probiotic augmented the vaccine's protective capacity.

Demonstration of the efficacy of a Salmonella Enteritidis live vaccine for chickens according to the current European Pharmacopoeia Monograph

Since 2013 the efficacy of new live Salmonella Enteritidis (SE) vaccines for chickens needs to be demonstrated according to European Pharmacopoeia Monograph 04/2013:2520 to receive approval in the EU. The purpose of this study was to determine whether a vaccine licensed since 1999 could also fulfil the required tests of the current guideline. For this, Salmonella-free chickens (n = 50) were vaccinated on their 2nd, 46th and 84th day of life with the live attenuated S. Enteritidis strain IDT No. 441/014. Non-vaccinated control animals (n = 50) were kept accordingly. To demonstrate the duration of immunity 20 animals of each group were challenge infected 65 weeks after the last vaccination with a virulent SE (PT 4) strain. According to the monograph, cloacal swabs were taken 3, 5, 7, 10 and 14 days post challenge (dpc). Tissue samples of liver, spleen, caeca, ovaries and oviduct were collected during necropsy of 10 animals per group on 7 and 14 dpc, respectively. All samples were analysed bacteriologically regarding the presence of the challenge strain. The number of challenge strain positive tissue samples and cloacal swabs was significantly reduced in vaccinated animals (p < 0.05). Therefore, the vaccine strain complied with the EP guideline. This study is the first that demonstrates the efficacy of this vaccine according to the current regulations. However, efficacy could also be shown during the development of the vaccine but by use of another animal model that comprised fewer animals per group. The use of this model is no longer accepted by EU regulatory authorities. The results need discussion in context with the 3R principle.

Overexpressing ovotransferrin and avian β-defensin-3 improves antimicrobial capacity of chickens and poultry products

Zoonotic and foodborne diseases pose a significant burden, decreasing both human and animal health. Modifying chickens to overexpress antimicrobials has the potential to decrease bacterial growth on poultry products and boost chicken innate immunity. Chickens overexpressing either ovotransferrin or avian β-defensin-3 (AvβD3) were generated using Tol-2 transposons. Transgene expression at the RNA and protein level was seen in egg white, breast muscle, and serum. There were significant differences in the immune cell populations in the blood, bursa, and spleen associated with transgene expression including an increased proportion of CD8+ cells in the blood of ovotransferrin and AvβD3 transgenic birds. Expression of the antimicrobials inhibited the in vitro growth of human and chicken bacterial pathogens and spoilage bacteria. For example, transgene expression significantly reduced growth of aerobic and coliform bacteria in breast muscle and decreased the growth of Salmonella enterica in egg white. Overall these results indicate that overexpression of antimicrobials in the chicken can impact the immune system and increase the antimicrobial capacity of poultry products.

Immunisation of chickens with live Salmonella vaccines - Role of booster vaccination

It is accepted that booster vaccinations of chickens with live Salmonella vaccines are essential part of vaccinations schemes to induce an effective adaptive immune response. As manufacturer of registered live Salmonella vaccines recommend different times of booster the question raises whether the duration between the first and second immunisation might influence the protective effect against Salmonella exposure. Chickens were immunised with a live Salmonella Enteritidis vaccine on day 1 of age followed by a booster vaccination at different intervals (day 28, 35 or 42 of age) to study the effects on the colonisation and invasion of the Salmonella vaccine strain, the humoral immune response and the efficacy against infection with Salmonella Enteritidis on day 56 of age. Immunisation of all groups resulted in a very effective adaptive immune response and a high degree of protection against severe Salmonella exposure, however, the time of booster had only an unverifiable influence on either the colonisation of the vaccine strain, the development of the humoral immune response or the colonisation of the Salmonella challenge strain. Therefore, the first oral immunisation of the chicks on day 1 of age seems to be of special importance and prerequisite for the development of the effective immune response. A booster immunisation should be carried out, however, the time of booster may vary between week 3 and week 7 of age of the chickens without adversely impact on the efficacy of the adaptive immune response or the protective effects.

Oral vaccination with a live Salmonella Enteritidis/Typhimurium bivalent vaccine in layers induces cross-protection against caecal and internal organ colonization by a Salmonella Infantis strain

Salmonella is an important zoonotic agent, and poultry products remain one of the main sources of infection for humans. Salmonella Infantis is an emerging serotype in poultry worldwide, reflected by an increased prevalence in poultry flocks, on broiler meat and in human foodborne illness cases. In the current study, the efficacy of oral administration of a live monovalent Salmonella Enteritidis and a live bivalent Salmonella Enteritidis/Typhimurium vaccine, against a Salmonella Enteritidis and Infantis infection, was determined. Oral administration of the live vaccines to day-old chickens caused a decrease in caecal colonization by Salmonella Enteritidis, but not Infantis, at day 7, when challenged at day 2. Vaccination with the bivalent vaccine at day 1 resulted in a decreased spleen colonization by both Salmonella Infantis and Enteritidis. Twice (at day 1 and week 6) and thrice vaccination (at day 1, week 6 and 16) of laying hens with the bivalent vaccine resulted in a decreased caecal colonization by Salmonella Enteritidis and Infantis, and significantly lower oviduct colonization levels by Salmonella Enteritidis. These data show cross-protection against Salmonella Infantis by oral administration of live vaccine strains belonging to other serogroups.

An Attenuated Salmonella enterica Serovar Typhimurium Strain and Galacto-Oligosaccharides Accelerate Clearance of Salmonella Infections in Poultry through Modifications to the Gut Microbiome

Salmonella is estimated to cause one million foodborne illnesses in the United States every year. Salmonella-contaminated poultry products are one of the major sources of salmonellosis. Given the critical role of the gut microbiota in Salmonella transmission, a manipulation of the chicken intestinal microenvironment could prevent animal colonization by the pathogen. In Salmonella, the global regulator gene fnr (fumarate nitrate reduction) regulates anaerobic metabolism and is essential for adapting to the gut environment. This study tested the hypothesis that an attenuated Fnr mutant of Salmonella enterica serovar Typhimurium (attST) or prebiotic galacto-oligosaccharides (GOS) could improve resistance to wild-type Salmonella via modifications to the structure of the chicken gut microbiome. Intestinal samples from a total of 273 animals were collected weekly for 9 weeks to evaluate the impact of attST or prebiotic supplementation on microbial species of the cecum, duodenum, jejunum, and ileum. We next analyzed changes to the gut microbiome induced by challenging the animals with a wild-type Salmonella serovar 4,[5],12:r:- (Nal^r) strain and determined the clearance rate of the virulent strain in the treated and control groups. Both GOS and the attenuated Salmonella strain modified the gut microbiome but elicited alterations of different taxonomic groups. The attST produced significant increases of Alistipes and undefined Lactobacillus, while GOS increased Christensenellaceae and Lactobacillus reuteri The microbiome structural changes induced by both treatments resulted in a faster clearance after a Salmonella challenge.IMPORTANCE With an average annual incidence of 13.1 cases/100,000 individuals, salmonellosis has been deemed a nationally notifiable condition in the United States by the Centers for Disease Control and Prevention (CDC). Earlier studies demonstrated that Salmonella is transmitted by a subset of animals (supershedders). The supershedder phenotype can be induced by antibiotics, ascertaining an essential role for the gut microbiota in Salmonella transmission. Consequently, modulation of the gut microbiota and modification of the intestinal microenvironment could assist in preventing animal colonization by the pathogen. Our study demonstrated that a manipulation of the chicken gut microbiota by the administration of an attenuated Salmonella strain or prebiotic galacto-oligosaccharides (GOS) can promote resistance to Salmonella colonization via increases of beneficial microorganisms that translate into a less hospitable gut microenvironment.

Salmonella Enteritidis with double deletion in phoP fliC and a competitive exclusion culture elicit substantial additive protective effects against Salmonella exposure in newly hatched chicks

A live Salmonella Enteritidis vaccine (SE147N ΔphoP fliC), able to express both a homologous intestinal colonisation-inhibition effect and a systemic invasion-inhibition effect, was tested for its potential to generate a postulated additive protective effect in case of combined application with a competitive exclusion (CE) culture against Salmonella exposure in very young chicks. Both, SE147N ΔphoP fliC and the CE culture alone were highly protective against systemic and intestinal colonisation of the challenge strain in case of moderate Salmonella exposure, consequently, additive protective effects in combined use could not be detected. However, in case of high Salmonella Enteritidis challenge with 10⁶ cfu/bird at day 3 of life the combination of the ΔphoP fliC vaccine and the CE culture resulted in a protective effect much more pronounced than either of the single preparations and most substantial compared to untreated control birds. The term additive protective effects reflects the recognition that exclusion effects by gut flora cultures and inhibition effects by Salmonella vaccines are caused by different mechanisms.