Salmonella carrier state in chicken: comparison of expression of immune response genes between susceptible and resistant animals

Adaptive evolution in asymptomatic host confers MDR Salmonella with enhanced environmental persistence and virulence

As a common cause for food-borne diseases, the Salmonella spp. are generally prevalent among livestock, whereby they are likely to be transmitted to human via environmental contamination. To explore the potential mechanism for prevalence of MDR Salmonella and its risk for dissemination via contaminated environments, we profiled the colonization dynamics of MDR Salmonella in chicken, herein we found that an adaptive evolution, driven by mutagenesis in a small protein-encoding gene (STM14_1829), conferred the multidrug resistant (MDR) Salmonella with increased fitness in asymptomatic host. Then the mechanistic study demonstrated that only one amino acid substitution in small protein STM14_1829 rendered MDR Salmonella capable to better invade and persist in phagocytotic cells by modulating bacterial flagella overexpression. Concerningly, the evolved Salmonella was also more resilient to the potential stressors generally found in environments and food processing, including heat, cold, adverse pH and oxidations. It implied that the evolved subpopulations are plausibly more persistent in environments once they contaminated through animal manure or human excreta. Moreover, the evolution promoted the pathogenesis caused by MDR Salmonella in susceptible hosts, resulting in higher risk for dissemination of pathogens via contaminated environments. Together, our data provided the novel insights into that in vivo adaptive evolution benefits Salmonella colonization, persistence and pathogenesis, by promoting bacterial tolerance via modulating flagella expression. These findings may explain the rationale behind the increasing prevalence of certain MDR Salmonella clones in livestock and associated environment, and underscoring the need for advanced strategies to tackle the possible evolution of such zoonotic pathogens.

Impact of feed additives and host-related factors on bacterial metabolites, mucosal integrity and immune response in the ileum of broilers

The present study aimed to investigate the effect of age, breed, and sex of broilers, as well as a probiotic or phytobiotic product on mucosal morphology, bacterial metabolites, and immune traits in the ileum of broilers. A total of 2,880 one-day-old male and female broiler chicks from two breeds (Ross308® and Cobb500®) were randomly assigned to 72 pens. Broilers were offered a wheat-soybean diet without (CO), or with either a probiotic (PO; 2.4 × 109 CFU/kg of Bacillus subtilis DSM32324 and DSM32325 and B. amyloliquefaciens DSM25840) or a phytobiotic (PY; grape extract, 165 ppm procyanidin and 585 ppm polyphenols of the diet) product. The trial was conducted with a 3 × 2 × 2 factorial arrangement of diet, breed, and sex in a completely randomized design (6 replicate-pens per treatment). At day 7, 21, and 35, one chicken per pen was slaughtered for collecting ileal tissue to evaluate of histomorphology and mRNA expression, as well as ileal digesta to measure bacterial metabolites. Data were subjected to ANOVA (the main factors; age, diet, breed, and sex) and Four-Way ANOVA (interactions) using GLM procedure. Overall, the concentration of acetate and total short chain fatty acids reached the peak and lactate decreased to its lowest on day 21, but their concentrations at day 7 and 35 were similar (p > 0.05). Spermine, spermidine, and ammonia decreased after day 7, while putrescine and cadaverine increased after day 21 (p < 0.05). mRNA expression of cytokines, mucin 2 (MUC2) and claudin 5 (CLDN5) was similar; increased from day 7 to 21 and decreased afterward (p < 0.05). Villus height, crypt depth and villus surface area increased with age (p < 0.05). Acidic goblet cells (GC) number and density increased after day 21 (p < 0.05). Ross broilers showed higher D-lactate concentration and IFN-γ expression, while Cobb broilers had greater IL-4, IL-6 and TNF-α expression and higher total GC number (p < 0.05). Female displayed higher villus height and GC number and density (mixed and total GC) than male (p < 0.05). The effect of dietary treatment was not found on any investigated variables (p > 0.05). In conclusion, aging of broilers affected ileal histomorphology, cytokine expression, and barrier integrity, as well as bacterial activity. These observed impacts could be attributed to host-microbiota interaction and the direct effects of bacterial metabolites on intestinal cells and immune system.

Quantifying Enteropathogen Contamination along Chicken Value Chains in Maputo, Mozambique: A Multidisciplinary and Mixed-Methods Approach to Identifying High Exposure Settings

BACKGROUND

Small-scale poultry production is widespread and increasing in low- and middle-income countries (LMICs). Exposure to enteropathogens in poultry feces increases the hazard of human infection and related sequela, and the burden of disease due to enteric infection in children < 5 y in particular is substantial. Yet, the containment and management of poultry-associated fecal waste in informal settings in LMICs is largely unregulated.

OBJECTIVES

To improve the understanding of potential exposures to enteropathogens carried by chickens, we used mixed methods to map and quantify microbial hazards along production value chains among broiler, layer, and indigenous chickens in Maputo, Mozambique.

METHODS

To map and describe the value chains, we conducted 77 interviews with key informants working in locations where chickens and related products are sold, raised, and butchered. To quantify microbial hazards, we collected chicken carcasses (n = 75 ) and fecal samples (n = 136 ) from chickens along the value chain and assayed them by qPCR for the chicken-associated bacterial enteropathogens C. jejuni/coli and Salmonella spp.

RESULTS

We identified critical hazard points along the chicken value chains and identified management and food hygiene practices that contribute to potential exposures to chicken-sourced enteropathogens. We detected C. jejuni/coli in 84 (76%) of fecal samples and 52 (84%) of carcass rinses and Salmonella spp. in 13 (11%) of fecal samples and 16 (21%) of carcass rinses. Prevalence and level of contamination increased as chickens progressed along the value chain, from no contamination of broiler chicken feces at the start of the value chain to 100% contamination of carcasses with C. jejuni/coli at informal markets. Few hazard mitigation strategies were found in the informal sector.

DISCUSSION

High prevalence and concentration of C. jejuni/coli and Salmonella spp. contamination along chicken value chains suggests a high potential for exposure to these enteropathogens associated with chicken production and marketing processes in the informal sector in our study setting. We identified critical control points, such as the carcass rinse step and storage of raw chicken meat, that could be intervened in to mitigate risk, but regulation and enforcement pose challenges. This mixed-methods approach can also provide a model to understand animal value chains, sanitary risks, and associated exposures in other settings. https://doi.org/10.1289/EHP11761.

Phenotype Alterations in the Cecal Ecosystem Involved in the Asymptomatic Intestinal Persistence of Paratyphoid Salmonella in Chickens

The gastrointestinal ecosystem involves interactions between the host, gut microbiota, and external environment. To colonize the gut of poultry, Salmonella must surmount barriers levied by the intestine including mucosal innate immune responses and microbiota-mediated niche restrictions. Accordingly, comprehending Salmonella intestinal colonization in poultry requires an understanding of how the pathogen interacts with the intestinal ecosystem. In chickens, the paratyphoid Salmonella have evolved the capacity to survive the initial immune response and persist in the avian ceca for months without triggering clinical signs. The persistence of a Salmonella infection in the avian host involves both host defenses and tolerogenic defense strategies. The initial phase of the Salmonella-gut ecosystem interaction is characteristically an innate pro-inflammatory response that controls bacterial invasion. The second phase is initiated by an expansion of the T regulatory cell population in the cecum of Salmonella-infected chickens accompanied by well-defined shifts in the enteric neuro-immunometabolic pathways that changes the local phenotype from pro-inflammatory to an anti-inflammatory environment. Thus, paratyphoid Salmonella in chickens have evolved a unique survival strategy that minimizes the inflammatory response (disease resistance) during the initial infection and then induces an immunometabolic reprogramming in the cecum that alters the host defense to disease tolerance that provides an environment conducive to drive asymptomatic carriage of the bacterial pathogen.

Suppressive modulation of host immune responses by Dermanyssus gallinae infestation

The poultry red mite (Dermanyssus gallinae, PRM) is a blood-sucking ectoparasite in chickens and is one of the most serious threats to poultry farms. Mass infestation with PRMs causes various health problems in chickens, resulting in significant productivity reduction in the poultry industry. Infestation with hematophagous ectoparasites, such as ticks, induces host inflammatory and hemostatic reactions. On the other hand, several studies have reported that hematophagous ectoparasites secrete various immunosuppressants from their saliva to suppress host immune responses to maintain blood sucking. Here, we examined the expression of cytokines in peripheral blood cells to investigate whether PRM infestation affects immunological states in chickens. In PRM-infested chickens, anti-inflammatory cytokines, IL-10 and TGF-β1, and immune checkpoint molecules, CTLA-4 and PD-1, were highly expressed compared to noninfested chickens. PRM-derived soluble mite extracts (SME) upregulated the gene expression of IL-10 in peripheral blood cells and HD-11 chicken macrophages. In addition, SME suppressed the expression of interferons and inflammatory cytokines in HD-11 chicken macrophages. Moreover, SME induces the polarization of macrophages into anti-inflammatory phenotypes. Collectively, PRM infestation could affect host immune responses, especially suppress the inflammatory responses. Further studies are warranted to fully understand the influence of PRM infestation on host immunity.

Alterations in bacterial metabolites, cytokines, and mucosal integrity in the caecum of broilers caused by feed additives and host-related factors

A total of 2,880 one-day-old male and female broiler chicks from two breeds, Ross308 and Cobb500 were randomly assigned to 72 pens. Broilers were offered three diets: a wheat-soybean diet without (CO), or with either a probiotic (probiotic; 2.4 x 10⁹ CFU/kg diet of Bacillus subtilis DSM32324 and DSM32325 and B. amyloliquefaciens DSM25840) or a phytobiotic (phytobiotic; grape extract with 165 ppm procyanidin and 585 ppm polyphenol) product. The trial was conducted with a 3 × 2 × 2 factorial arrangement of diet, breed and sex in a completely randomized design and consisted of 6 replicate-pens per treatment (40 birds per pen). At day 7, 21, and 35, one chicken per pen was slaughtered for caecal sampling to quantify bacterial metabolites (digesta) as well as evaluate mRNA abundance and histomorphology (tissue). Data were subjected to ANOVA using GLM procedure to evaluate age, diet, breed and sex and their interactions. Spearman’s correlation (r) was analyzed between metabolite concentration and mRNA abundance. Overall, the concentration of short chain fatty acids increased with age, while lactate decreased from day 7 to 21 (p < 0.05). The mRNA abundance of IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-17α, IL-18, IFN-γ and TGF-β2 increased with age but IL-1β and TNF-α increased in abundance from day 7 to 21 and then decreased (p < 0.05). Abundance of MUC2 and CLDN5 increased after day 21 (p < 0.05). Caecal crypt depth increased with age (p < 0.05). Acidic goblet cell (GC) number peaked at day 21 (p < 0.05), while mixed GC number was not affected by age. A few impacts of breed, diet and interactions on the investigated variables showed no meaningful biological pattern. Propionate positively correlated with all cytokines investigated (r = 0.150–0.548), except TNF-α. Lactate negatively correlated with pro-inflammatory cytokines like IL-1β (r = −0.324). Aging affected caecal histomorphology, bacterial activity and genes responsible for barrier integrity and inflammatory response. This effect could be attributed to the interaction between gut microbiota and immune system as well as the direct effect of metabolites on gut histomorphology and cytokine mRNA abundance.

Comparative analysis of the caecal tonsil transcriptome in two chicken lines experimentally infected with Salmonella Enteritidis

Managing Salmonella enterica Enteritidis (SE) carriage in chicken is necessary to ensure human food safety and enhance the economic, social and environmental sustainability of chicken breeding. Salmonella can contaminate poultry products, causing human foodborne disease and economic losses for farmers. Both genetic selection for a decreased carriage and gut microbiota modulation strategies could reduce Salmonella propagation in farms. Two-hundred and twenty animals from the White Leghorn inbred lines N and 61 were raised together on floor, infected by SE at 7 days of age, transferred into isolators to prevent oro-fecal recontamination and euthanized at 12 days post-infection. Caecal content DNA was used to measure individual Salmonella counts (ISC) by droplet digital PCR. A RNA sequencing approach was used to measure gene expression levels in caecal tonsils after infection of 48 chicks with low or high ISC. The analysis between lines identified 7516 differentially expressed genes (DEGs) corresponding to 62 enriched Gene Ontology (GO) Biological Processes (BP) terms. A comparison between low and high carriers allowed us to identify 97 DEGs and 23 enriched GO BP terms within line 61, and 1034 DEGs and 288 enriched GO BP terms within line N. Among these genes, we identified several candidate genes based on their putative functions, including FUT2 or MUC4, which could be involved in the control of SE infection, maybe through interactions with commensal bacteria. Altogether, we were able to identify several genes and pathways associated with differences in SE carriage level. These results are discussed in relation to individual caecal microbiota compositions, obtained for the same animals in a previous study, which may interact with host gene expression levels for the control of the caecal SE load.

Two In Vivo Models to Study Salmonella Asymptomatic Carrier State in Chicks

In chicken, Salmonella Enteritidis and Salmonella Typhimurium, the two main serotypes isolated in human infections, can persist in the host organism for many weeks and up to many years without causing any symptoms. This persistence generally occurs after a short systemic infection that may either lead to death of very young birds or develop into cecal asymptomatic persistence, which is often accompanied by a high level of bacterial excretion, facilitating Salmonella transmission to counterparts. Here we describe two models of chick infection. The first model reproduces well the poultry infection in farm flocks. Numerous reinfections and animal-animal recontaminations occur leading to a high level of cecal colonization and fecal excretion in all chicks in the flock, over several weeks. In the second model, these animal reinfections and recontaminations are hampered leading to heterogeneity of infection characterized by the presence of low and super-shedders. This model allows for more mechanistic studies of Salmonella/chicks interactions as animal recontaminations are lowered.

Effects of Salmonella enterica ser. Enteritidis and Heidelberg on host CD4+CD25+ regulatory T cell suppressive immune responses in chickens

Poultry infected with Salmonella mount an immune response initially, however the immune responses eventually disappear leading the bird to be a carrier of Salmonella. The hypothesis of this study is that Salmonella infection induces T regulatory cell numbers and cytokine production and suppress host T cells locally in the gut to escape the host immune responses. An experiment was conducted to comparatively analyze the effect of S. enterica ser. Enteritidis (S. Enteritidis) and S. enterica ser. Heidelberg (S. Heidelberg) infection on CD4⁺CD25⁺ T regulatory cell properties in chickens. A total of 144 broiler chicks were randomly distributed into three experimental groups of non-infected control, S. Enteritidis infected and S. Heidelberg infected groups. Chickens were orally inoculated with PBS (control) or 5x10⁶ CFU/mL of either S. Enteritidis or S. Heidelberg at 3 d of age. Each group was replicated in six pens with eight chickens per pen. Chickens infected with S. Enteritidis had 6.2, 5.4, and 3.8 log₁₀ CFU/g, and chickens infected with S. Heidelberg had 7.1, 4.8, and 4.1 log₁₀ CFU/g Salmonella in the cecal contents at 4, 11, and 32 dpi, respectively. Both S. Enteritidis and S. Heidelberg were recovered from the liver and spleen 4 dpi. At 4, 11, and 32 dpi, chickens infected with S. Enteritidis and S. Heidelberg had increased CD4⁺CD25⁺ cell numbers as well as IL-10 mRNA transcription of CD4⁺CD25⁺ cells compared to that in the control group. CD4⁺CD25⁺ cells from S. Enteritidis- and S. Heidelberg-infected chickens and restimulated with 1 μg antigen in vitro, had higher (P < 0.05) IL-10 mRNA transcription than the CD4⁺CD25⁺ cells from the non-infected controls Though at 4dpi, chickens infected with S. Enteritidis and S. Heidelberg had a significant (P < 0.05) increase in CD4⁺CD25^- IL-2, IL-1β, and IFNγ mRNA transcription, the CD4⁺CD25^- IL-2, IL-1β, and IFNγ mRNA transcription, were comparable to that in the control group at 11 and 32dpi identifying that the host inflammatory response against Salmonella disappears at 11 dpi. It can be concluded that S. Enteritidis and S. Heidelberg infection at 3 d of age induces a persistent infection through inducing CD4⁺CD25⁺ cells and altering the IL-10 mRNA transcription of CD4⁺CD25⁺ cell numbers and cytokine production in chickens between 3 to 32 dpi allowing chickens to become asymptomatic carriers of Salmonella after 18 dpi.

Effects of Essential Oils-Based Supplement and Salmonella Infection on Gene Expression, Blood Parameters, Cecal Microbiome, and Egg Production in Laying Hens

One of the main roles in poultry resistance to infections caused by Salmonella is attributed to host immunity and intestinal microbiota. We conducted an experiment that involved challenging Lohmann White laying hens with Salmonella Enteritidis (SE), feeding them a diet supplemented with an EOs-based phytobiotic Intebio^®. At 1 and 7 days post-inoculation, the expression profiles of eight genes related to immunity, transport of nutrients in the intestine, and metabolism were examined. Cecal microbiome composition and blood biochemical/immunological indices were also explored and egg production traits recorded. As a result, the SE challenge of laying hens and Intebio^® administration had either a suppressive or activating effect on the expression level of the studied genes (e.g., IL6 and BPIFB3), the latter echoing mammalian/human tissue-specific expression. There were also effects of the pathogen challenge and phytobiotic intake on the cecal microbiome profiles and blood biochemical/immunological parameters, including those reflecting the activity of the birds' immune systems (e.g., serum bactericidal activity, β-lysine content, and immunoglobulin levels). Significant differences between control and experimental subgroups in egg performance traits (i.e., egg weight/number/mass) were also found. The phytobiotic administration suggested a positive effect on the welfare and productivity of poultry.

Gut microbiota composition before infection determines the Salmonella super- and low-shedder phenotypes in chicken

Heterogeneity of infection and extreme shedding patterns are common features of animal infectious diseases. Individual hosts that are super-shedders are key targets for control strategies. Nevertheless, the mechanisms associated with the emergence of super-shedders remain largely unknown. During chicken salmonellosis, a high heterogeneity of infection is observed when animal-to-animal cross-contaminations and reinfections are reduced. We hypothesized that unlike super-shedders, low-shedders would be able to block the first Salmonella colonization thanks to a different gut microbiota. The present study demonstrates that (i) axenic and antibiotic-treated chicks are more prone to become super-shedders; (ii) super or low-shedder phenotypes can be acquired through microbiota transfer; (iii) specific gut microbiota taxonomic features determine whether the chicks develop a low- and super-shedder phenotype after Salmonella infection in isolator; (iv) partial protection can be conferred by inoculation of four commensal bacteria prior to Salmonella infection. This study demonstrates the key role plays by gut microbiota composition in the heterogeneity of infection and pave the way for developing predictive biomarkers and protective probiotics.

Dietary supplementation with vitamin C ameliorates the adverse effects of Salmonella Enteritidis-challenge in broilers by shaping intestinal microbiota

Salmonella Enteritidis (SE) infection is not only a leading cause of poor production performance and compromised animal welfare in broilers but also a potential threat to public health. Two experiments were conducted to evaluate the effects of dietary supplemental vitamin C (VC) on SE challenged-broilers. In experiment 1, one hundred eighty 1-day-old Arbor Acre broilers were randomly allocated into 3 treatments, with 0, 500, or 1,000 mg/kg VC included in the diet. In experiment 2, dietary VC at 0 or 500 mg/kg, with or without SE challenge was applied in a 2 × 2 factorial arrangement in 6 randomized complete blocks. In experiment 1, addition with 500 mg/kg VC increased BW and infectious bursal disease (IBD) titer of broilers on 35 D (P < 0.05), whereas 1,000 mg/kg VC had no effects on the IBD titer (P > 0.05) compared with the control group. In experiment 2, SE challenge depressed BW on 11 and 21 D (P < 0.05 and P = 0.088, respectively), whereas increased mortality and hepatic bacterial translocation (P < 0.05) on 21 D. Further, SE challenge resulted in lower villus height in jejunum, lower microbial richness, and diversity, whereas higher abundance of Enterobacteriaceae in cecum (P < 0.05). Importantly, supplementation with VC increased BW on both 21 and 35 D (P < 0.05 and P = 0.088, respectively) and enhanced the intestinal health by improving villus morphology and microbial structure as indicated by higher cecal microbial richness and Firmicutes to Bacteroidetes ratio, while lower abundance of Enterobacteriaceae (P < 0.05). In addition, birds fed with 500 mg/kg VC in the diet had significantly increased jejunal secretory immunoglobulin A levels, T lymphocytes stimulation index, and serum total antioxidant capability compared with groups without VC (P < 0.05). In conclusion, SE challenge induced lower production performance and higher mortality in broilers. However, dietary supplementation with VC ameliorated SE-caused damage in broilers by improving the intestinal health, partly mediated by shaping the structure of cecal microbiota.

Evaluation of in-vivo anti-Salmonella activity of Uvaria chamae, Lantana camara and Phyllantus amarus used in Benin, West Africa

BACKGROUND

Uvaria chamae (Annonaceae), Phyllantus amarus (Phyllantaceae) and Lantana camara (Verbenaceae) are empirically alleged to be used as Beninese medicinal plants in the treatment of salmonellosis. This study aimed to produce scientific data on in vitro and in vivo efficacy of Uvaria chamae, Lantana camara and Phyllantus amarus on multiresistant Salmonella spp isolated in Benin.

RESULTS

After performing in vitro tests on aqueous and ethanolic extracts of these plants, only the aqueous extract of Uvaria chamae (leaves) showed the best anti-Salmonella's activity and was used for this in vivo experiment. The induction of salmonellosis revealed 9 × 108 CFU/ml was the optimal concentration triggering and maintaining symptoms in chicks. This infective concentration was used for in vivo assessment. Twenty-four hours post inoculation, the symptoms of salmonellosis (wet cloaca, diarrhea stools and somnolence) were observed in infected groups. After 7 days of treatment, the reduction of bacterial load at 100 mg/L, 200 mg/L, 400 mg/L of the extract was respectively 85%, 52.38% and 98% for Uvaria chamae, Phyllantus amarus and Lantana camara in the chick's groups infected with Salmonella Typhimurium ATCC 14028. On the other hand, colistin completely cancelled the bacterial load (reduction rate of 100%). With the groups infected with Salmonella spp (virulent strain), the reduction rate of bacterial load at 100 mg/L, 200 mg/L, 400 mg/L of extract was 0%, 98.66%, and 99.33%. The extracts at 200 and 400 mg/L were more active than colistin, which reduced the bacterial load by 33.33%. The toxicity tests did not show any negative effect of Colistin and the Uvaria chamae's extract on the biochemical and hematological parameters of the chicks.

CONCLUSION

The aqueous extract of Uvaria chamae is active in vitro and in vivo on multiresistant strains of Salmonella enterica. This plant is a good candidate for the development of an improved traditional medicine for the management of salmonellosis.

Research Note: Correlation analysis of interleukin-6, interleukin-8, and C-C motif chemokine ligand 2 gene expression in chicken spleen and cecal tissues after Eimeria tenella infection in vivo

IL-6, IL-8, and C-C motif chemokine ligand 2 (CCLi2) are important factors in inflammatory and immune responses. To investigate their relationships in the spleen and cecum and between coccidiosis-infected and uninfected states, we performed quantitative real-time PCR to compare the relative expression difference of IL-6, IL-8, and CCLi2 in the same tissues between the infection and control groups. In addition, the correlations of the relative expression levels of these 3 genes were determined in the same and different tissues within the same group. The results showed that the expression levels of IL-6, IL-8, and CCLi2 in the spleen and cecum of the infected group were all higher than those of the uninfected group (P < 0.05). The correlation coefficients among the IL-6, IL-8, and CCLi2 expression levels in the spleen or cecum were all positive in both the infection and control groups. In the spleen tissues, CCLi2 expression was strongly correlated with IL-6 and IL-8 in the uninfected group (P < 0.01), and the correlation coefficients reached 0.853 (R² = 0.728) and 0.996 (R² = 0.992), respectively. The expression of CCLi2 was also strongly correlated with IL-8 (R reached 0.890, R² = 0.792) in the infected group. In the cecal tissues, the expression levels of the 3 genes were all extremely significantly correlated in the uninfected group (P < 0.01), and the correlation coefficients ranged from 0.498 to 0.765, indicating moderate correlations. The expression of IL-6 was extremely significantly positively correlated with IL-8 and CCLi2 in the infected group (P < 0.01), with moderate correlations (R ranged from 0.469–0.639). In addition, the expression levels of the 3 genes were not significantly correlated (P > 0.05) between the spleen and cecum tissues in either the infection group or the control group. These results indicate that IL-6, IL-8, and CCLi2 were correlated and play an important role in coccidiosis infection of Jinghai yellow chicken. Our data also provide a basis for further exploring the role of these 3 genes in genetic breeding for coccidiosis resistance.

In Ovo Administration of Innate Immune Stimulants and Protection from Early Chick Mortalities due to Yolk Sac Infection

Omphalitis or yolk sac infection (YSI) and colibacillosis are the most common infectious diseases that lead to high rates of early chick mortalities (ECMs) in young chicks. Out of numerous microbial causes, avian pathogenic Escherichia coli (APEC) or extraintestinal pathogenic E. coli infections are considered the most common cause of these conditions. YSI causes deterioration and decomposition of yolk, leading to deficiency of necessary nutrients and maternal antibodies, retarded growth, poor carcass quality, and increased susceptibility to other infections, including omphalitis, colibacillosis, and respiratory tract infection. Presently, in ovo injection of antibiotics, heavy culling, or after hatch use of antibiotics is practiced to manage ECM. However, increased antibiotic resistance and emergence of "super bugs" associated with use or misuse of antibiotics in the animal industry have raised serious concerns. These concerns urgently require a focus on host-driven nonantibiotic approaches for stimulation of protective antimicrobial immunity. Using an experimental YSI model in newborn chicks, we evaluated the prophylactic potential of three in ovo-administered innate immune stimulants and immune adjuvants for protection from ECM due to YSI. Our data have shown >80%, 65%, and 60% survival with in ovo use of cytosine-phosphodiester-guanine (CpG) oligodeoxynucleotides (ODN), polyinosinic:polycytidylic acid, and polyphosphazene, respectively. In conclusion, data from these studies suggest that in ovo administration of CpG ODN may serve as a potential candidate for replacement of antibiotics for the prevention and control of ECM due to YSI in young chicks.

Evaluation of different live Salmonella enteritidis vaccine schedules administered during layer hen rearing to reduce excretion, organ colonization, and egg contamination

Salmonellosis caused by Salmonella Enteritidis is a widespread zoonosis and poultry products are an important source of infection. This study was carried out to evaluate the protection of different vaccination schedules in layers using a live commercial attenuated Salmonella Enteritidis vaccine based on strain Sm24/Rif12/Ssq (AviPro® Salmonella Vac E, ELANCO) during rearing and egg production. Three hundred and fifty Salmonella-free chickens were distributed into 7 vaccinated groups and 1 unvaccinated group. Different vaccination schedules were performed combining either 1, 2, or 3 oral gavage doses. Chickens from Group A, B, and C were vaccinated once, either at the first day, at 7 or 16 wk old, respectively. Chickens from Group D were vaccinated twice-at the first day and 7 wk old. Chickens from Group E were vaccinated twice-at the first day and 16 wk old. Chickens from Group F were vaccinated twice-at 7 and 16 wk old. Chickens from Group G were vaccinated 3 times, following the manufacturer's recommendation: at the first day, 7 and 16 wk old. Chickens from Group H remained unvaccinated. Five challenge trials numbered 1 to 5 were carried out at 8, 12, 16, 29, and 55 wk old, respectively. After challenge, chickens were sampled by cloacal swabbing and, after euthanasia, livers, ovaries, spleens, and cecal contents were cultured to isolate S. Enteritidis. Additionally, eggs were collected after challenge and cultured to isolate S. Enteritidis on egg shells (Trials 4 and 5). Protection against experimental infection with a virulent nalidixic acid resistant S. Enteritidis strain K285/94, was evaluated by measuring reduction of excretion, colonization, invasion into organs, eggshell contamination, and egg production. The live S. Enteritidis vaccine protected the hens by reducing S. Enteritidis excretion, isolation from organs, and egg contamination. Higher protection throughout laying period was afforded after administration of three vaccine doses during rearing period.

The effects of the supplementation of multi-strain probiotics on intestinal microbiota, metabolites and inflammation of young SPF chickens challenged with Salmonella enterica subsp. enterica

This study assessed the effect of probiotics on cecal microbiota, cecal short-chain fatty acids (SCFAs), and the gene expression of cytokines in young specific-pathogen-free (SPF) chickens infected with S. enterica subsp. enterica. One-day-old SPF chickens (n = 105) were randomly assigned to one of the three treatment groups: control (Cont) group, Salmonella-infected (Sal) group, and a Salmonella-infected group treated with multi-strain probiotics (ProSal group). All chickens except those in the Cont group were challenged orally with 1 × 10⁸  cfu/ml of Salmonella 4 days after hatching. Chickens in the Sal group exhibited more abundance of Proteobacteria than those in the Cont and ProSal groups. At the genus level, chickens in ProSal group exhibited increased numbers of Lactobacillus and Oscillospira compared with those in the other groups. Chickens in the ProSal group exhibited a significant increase of cecal SCFAs compared with chickens in the Sal group. Chickens in the ProSal group exhibited increased gene expression of anti-inflammatory cytokines, IL-10 and TGF-β4, and decreased expression of the proinflammatory cytokine, IFN-γ, in the cecal tonsil compared with those in the Sal group. The results of this study indicated that the administration of probiotics can modulate microbiota, SCFAs, and immunomodulatory activity in SPF chickens.

Deciphering desirable immune responses from disease models with resistant and susceptible chickens

Coccidiosis and necrotic enteritis (NE) are among the most significant diseases affecting the poultry industry. These diseases have become more prominent in the wake of policies to reduce the use of antibiotics in animal production. This has led to more research focused on better understanding the immune system and its responses to pathogen challenge, and thus developing informed strategies to exploit immune responses that can support enhanced disease resistance and growth performance. Some chicken breeds and lines show greater resistance or susceptibility to various diseases, and thus these birds maybe able to shed light on immune processes or pathways that contribute to the more resistant/susceptible state. This review attempts to identify potentially important genes that show some consistency in (relative) up or downregulation in key tissues between the resistant and susceptible chickens. For coccidiosis and NE, relative downregulation of IL-10 and (slightly less consistently) upregulation of IFN-γ appear to be features of more resistant birds. Data for IFN-α, IL-12, and IL-17D are currently less consistent. Gene expression data from NE studies have identified some potentially interesting, perhaps less well understood, immune-related genes (e.g., TCF12, BCL2, IRF2, TRAF3, TAB3, etc.,) that maybe associated with the resistant and/or susceptible phenotype. Salmonella and Campylobacter are important foodborne pathogens harbored by the chicken intestinal tract, while infectious bursal disease and infectious bronchitis are also important viral diseases of poultry. We, therefore, consider whether there are consistent features from resistant/susceptible disease models with these pathogens that relate to findings from the coccidiosis and NE studies. It is not anticipated that ideal immune responses to these pathogens will be identical but rather that consistent elements maybe identified that could help inform breeding or alternative strategies to support general disease resistance and enhanced (and efficient) flock productivity.

Dose-dependent differential resistance of inbred chicken lines to avian pathogenic Escherichia coli challenge

Avian pathogenic E. coli (APEC) cause severe respiratory and systemic disease. To address the genetic and immunological basis of resistance, inbred chicken lines were used to establish a model of differential resistance to APEC, using strain O1 of serotype O1:K1:H7. Inbred lines 7₂, 15I and C.B12 and the outbred line Novogen Brown were inoculated via the airsac with a high dose (10⁷ colony-forming units, CFU) or low dose (10⁵ CFU) of APEC O1. Clinical signs, colibacillosis lesion score and bacterial colonization of tissues after high dose challenge were significantly higher in line 15I and C.B12 birds. The majority of the 15I and C.B12 birds succumbed to the infection by 14 h post-infection, whilst none of the line 7₂ and the Novogen Brown birds developed clinical signs. No difference was observed after low dose challenge. In a repeat study, inbred lines 7₂ and 15I were inoculated with low, intermediate or high doses of APEC O1 ranging from 10⁵ to 10⁷ CFU. The colonization of lung was highest in line 15I after high dose challenge and birds developed clinical signs; however, colonization of blood and spleen, clinical signs and lesion score were not different between lines. No difference was observed after intermediate or low dose challenge. Ex vivo, the phagocytic and bactericidal activity of lung leukocytes from line 7₂ and 15I birds did not differ. Our data suggest that although differential resistance of inbred lines 7₂, 15I and C.B12 to APEC O1 challenge is apparent, it is dependent on the infectious dose. Research Highlights Lines 15I and C.B12 are more susceptible than line 7₂ to a high dose of APEC O1. Differential resistance is dose-dependent in lines 15I and 7₂. Phagocytic and bactericidal activity is similar and dose independent.

Effect of dietary Bacillus coagulans supplementation on growth performance and immune responses of broiler chickens challenged by Salmonella enteritidis

This study was conducted to evaluate the protective efficacy of dietary Bacillus coagulans (B. coagulans) supplementation in birds receiving Salmonella enteritidis (SE). Two hundred and forty 1-day-old Cobb broilers were randomly assigned to 2 × 2 factorial arrangements of treatments with 2 levels of dietary B. coagulans (0 or 400 mg/kg) and 2 levels of SE challenge (0 or 1 × 109 SE between d 9 to 11). Results showed that SE infection did not affect growth performance, but caused intestinal inflammation and barrier function impairment by reducing intestinal goblet cells and beneficial bacteria numbers, increasing cecal Salmonella colonization and liver Salmonella invasion, downregulating jejunal mucin-2 (at 7 and 17 d post-infection, DPI), TLR2 (at 7 and 17 DPI), TLR4 (at 17 DPI), TNFSF15 (at 7 and 17 DPI) gene mRNA levels, and upregulating jejunal IFN-γ mRNA levels (at 17 DPI) compared to uninfected birds. Moreover, SE infection also elevated the concentration of jejunal anti-Salmonella IgA and sera anti-Salmonella IgG compared to uninfected birds. However, chickens received B. coagulans diets showed significant increase in body weight gain and weight gain to feed intake ratio from d 15 to 21, alkaline phosphatase activity (at 7 DPI), cecal Lactobacilli and Bifidobacterium numbers (at 7 DPI; at 17 DPI), villous height: crypt ratio (at 17 DPI), and goblet cell numbers (at 7 and 17 DPI), whereas exhibiting reduced jejunal crypt depth (at 17 DPI), cecal Escherichia coli (at 7, 17, and 31 DPI), and Salmonella (at 7 and 17 DPI) levels compared with the non-supplemented birds, regardless of SE infection. In addition, B. coagulans supplement upregulated lysozyme mRNA levels (at 17 DPI), downregulated IFN-γ mRNA levels (at 7 and 17 DPI), showed an increased trend in Fowlicidin-2 mRNA levels (at 7 DPI) and a reduced trend in liver Salmonella load compared to the non-supplemented control. These data indicated that B. coagulans has a protective effect in SE infected broilers.

Role of systemic infection, cross contaminations and super-shedders in Salmonella carrier state in chicken

Carriage of Salmonella is often associated with a high level of bacterial excretion and generally occurs after a short systemic infection. However, we do not know whether this systemic infection is required or whether the carrier-state corresponds to continuous reinfection or real persistence in caecal tissue. The use of a Salmonella Enteritidis bamB mutant demonstrated that a carrier-state could be obtained in chicken in the absence of systemic infection. The development of a new infection model in isolator showed that a marked decrease in animal reinfection and host-to-host transmission between chicks led to a heterogeneity of S. Enteritidis excretion and colonization contrary to what was observed in cages. This heterogeneity of infection was characterized by the presence of super-shedders, which constantly disseminated Salmonella to the low-shedder chicks, mainly through airborne movements of contaminated dust particles. The presence of super-shedders, in the absence of host-to-host transmission, demonstrated that constant reinfection was not required to induce a carrier-state. Finally, our results suggest that low-shedder chicks do not have a higher capability to destroy Salmonella but instead can block initial Salmonella colonization. This new paradigm opens new avenues to improve understanding of the carrier-state mechanisms and to define new strategies to control Salmonella infections.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.

Differential Levels of Cecal Colonization by Salmonella Enteritidis in Chickens Triggers Distinct Immune Kinome Profiles

Salmonella enterica serovar Enteritidis are facultative intracellular bacteria that cause disease in numerous species. Salmonella-related infections originating from poultry and/or poultry products are a major cause of human foodborne illness with S. Enteritidis the leading cause worldwide. Despite the importance of Salmonella to human health and chickens being a reservoir, little is known of the response to infection within the chicken gastrointestinal tract. Using chicken-specific kinome immune peptide arrays we compared a detailed kinomic analysis of the chicken jejunal immune response in a single line of birds with high and low Salmonella loads. Four-day-old chicks were challenged with S. Enteritidis (10⁵ cfu) and cecal content and a section of jejunum collected at three times: early [4-7 days post-infection (dpi)], middle (10-17 dpi), and late (24-37 dpi). Salmonella colonization was enumerated and birds with the highest (n = 4) and lowest (n = 4) loads at each time were selected for kinomic analyses. Key biological processes associated with lower loads of Salmonella clustered around immune responses, including cell surface receptor signaling pathway, positive regulation of cellular processes, defense response, innate immune response, regulation of immune response, immune system process, and regulation of signaling. Further evaluation showed specific pathways including chemokine, Jak-Stat, mitogen activated protein kinase, and T cell receptor signaling pathways were also associated with increased resistance. Collectively, these findings demonstrate that it is possible to identify key mechanisms and pathways that are associated with increased resistance against S. Enteritidis cecal colonization in chickens. Therefore, providing a foundation for future studies to identify specific proteins within these pathways that are associated with resistance, which could provide breeders additional biomarkers to identify birds naturally more resistant to this important foodborne pathogen.

Effect of feeding soybean meal and differently processed peas on the gut mucosal immune system of broilers

Peas are traditionally used as a protein source for poultry. However, peas contain antinutritional factors (ANF), which are associated with the initiation of local and systemic immune reactions. The current study examined the effect of feeding raw or differently processed peas in comparison with feeding a soybean meal (SBM) based control diet (C) on the gut mucosal immune system of broilers in a 35 day feeding trial. In six replicates, a total of 360 one-day-old male broilers were randomly allocated to four different groups receiving C, or three treatment diets containing raw, fermented, and enzymatically pre-digested peas, each supplying 30% of required crude protein. After slaughtering, jejunal samples were taken for immunohistochemical, flow cytometric, and gene expression analyses. Investigations were focused on the topological distribution of intraepithelial leukocytes (villus tip, villus mid, and crypt region) as well as on the further characterization of the different intraepithelial lymphocytes (IEL) and concomitant pro- and anti-inflammatory cytokines. Broilers receiving the raw or processed pea diets had higher numbers of intraepithelial CD45+ leukocytes in the tip (P = 0.004) and mid region (P < 0.001) of villi than birds fed C. Higher numbers of intraepithelial CD3+ lymphocytes were found in the villus tip (P = 0.002) and mid region (P = 0.003) of birds fed raw or processed pea containing diets in comparison with those fed C. The flow cytometric phenotyping showed a similar relative distribution of IEL among the feeding groups. The expression of intestinal pro- and anti-inflammatory cytokines was affected by feeding the different diets only to a minor extent. To conclude, feeding of diets formulated with raw and processed peas in comparison with feeding a SBM control diet initiated mucosal immune responses in the jejunum of broilers indicated by a quantitative increase of intraepithelial T cells. Further research is needed in order to ascertain the specific factors which are responsible for observed local immune reactions and how these local reactions might affect the immune status and health of broilers.

Genetic differences in ChTLR15 gene polymorphism and expression involved in Salmonella enterica natural and artificial infection respectively, of Chinese native chicken breeds, with a focus on sexual dimorphism

Chicken Toll-like receptor 15 (ChTLR15) has been shown to participate in immune activation in response to various pathogens and in the innate defence against infection. Two genetically distinct Chinese breeds of chicken (Qinyuan Partridge and Baier breeds) were used to study the correlation between ChTLR15 single nucleotide polymorphisms and the natural infection status of salmonella in hens, and also to examine genetic and sex-specific effects on ChTLR15 mRNA expression in heterophils and spleen during acute infection with Salmonella enterica serovar Enteritidis (SE) from 1 to 10 days after experimental infection. Three single-nucleotide polymorphisms (G168A, C726T and A1166G) in a single exon of ChTLR15 were identified in the two breeds, but only C726T showed a significant association with salmonella infection. Compared with layer-type Baier chicks, meat-type Qingyuan chicks showed a higher tolerance for capture stress and (SE) infection, as measured, respectively, by the modified body weight of chicks in the control group and in the infection group. Meanwhile, ChTLR15 down-regulation in heterophils and up-regulation in spleen were involved in the response to pathogenic SE colonization during the acute infection period. These significant genetic effects in females led to greater differences in both innate and adaptive immune responses than those exhibited in males. These results suggest that genetics, time and gender play important roles in the modulation of ChTLR15 mRNA level elicited by the SE-mediated immune response differentially in the two genetically distinct breeds, with a focus on sexual dimorphism.

Immunometabolic Phenotype Alterations Associated with the Induction of Disease Tolerance and Persistent Asymptomatic Infection of Salmonella in the Chicken Intestine

The adaptation of Salmonella enterica to the eukaryotic host is a key process that enables the bacterium to survive in a hostile environment. Salmonella have evolved an intimate relationship with its host that extends to their cellular and molecular levels. Colonization, invasion, and replication of the bacteria in an appropriate host suggest that modification of host functions is central to pathogenesis. Intuitively, this subversion of the cell must be a complex process, since hosts are not inherently programmed to provide an environment conducive to pathogens. Hosts have evolved countermeasures to pathogen invasion, establishment, and replication through two types of defenses: resistance and tolerance. Resistance functions to control pathogen invasion and reduce or eliminate the invading pathogen. Research has primarily concentrated on resistance mechanisms that are mediated by the immune system. On the other hand, tolerance is mediated by different mechanisms that limit the damage caused by a pathogen’s growth without affecting or reducing pathogen numbers or loads. The mechanisms of tolerance appear to be separated into those that protect host tissues from the virulence factors of a pathogen and those that limit or reduce the damage caused by the host immune and inflammatory responses to the pathogen. Some pathogens, such as Salmonella, have evolved the capacity to survive the initial robust immune response and persist. The persistent phase of a Salmonella infection in the avian host usually involves a complex balance of protective immunity and immunopathology. Salmonella is able to stay in the avian ceca for months without triggering clinical signs. Chronic colonization of the intestinal tract is an important aspect of persistent Salmonella infection because it results in a silent propagation of bacteria in poultry stocks due to the impossibility to isolate contaminated animals. Data from our lab promote the hypothesis that Salmonella have evolved a unique survival strategy in poultry that minimizes host defenses (disease resistance) during the initial infection and then exploits and/or induces a dramatic immunometabolic reprogramming in the cecum that alters the host defense to disease tolerance. Unfortunately, this disease tolerance results in the ongoing human food safety dilemma.

Chicken-Specific Kinome Array Reveals that Salmonella enterica Serovar Enteritidis Modulates Host Immune Signaling Pathways in the Cecum to Establish a Persistence Infection

Non-typhoidal Salmonella enterica induces an early, short-lived pro-inflammatory response in chickens that is asymptomatic of clinical disease and results in a persistent colonization of the gastrointestinal (GI) tract that transmits infections to naïve hosts via fecal shedding of bacteria. The underlying mechanisms that control this persistent colonization of the ceca of chickens by Salmonella are only beginning to be elucidated. We hypothesize that alteration of host signaling pathways mediate the induction of a tolerance response. Using chicken-specific kinomic immune peptide arrays and quantitative RT-PCR of infected cecal tissue, we have previously evaluated the development of disease tolerance in chickens infected with Salmonella enterica serovar Enteritidis (S. Enteritidis) in a persistent infection model (4-14 days post infection). Here, we have further outlined the induction of an tolerance defense strategy in the cecum of chickens infected with S. Enteritidis beginning around four days post-primary infection. The response is characterized by alterations in the activation of T cell signaling mediated by the dephosphorylation of phospholipase c-γ1 (PLCG1) that inhibits NF-κB signaling and activates nuclear factor of activated T-cells (NFAT) signaling and blockage of interferon-γ (IFN-γ) production through the disruption of the JAK-STAT signaling pathway (dephosphorylation of JAK2, JAK3, and STAT4). Further, we measured a significant down-regulation reduction in IFN-γ mRNA expression. These studies, combined with our previous findings, describe global phenotypic changes in the avian cecum of Salmonella Enteritidis-infected chickens that decreases the host responsiveness resulting in the establishment of persistent colonization. The identified tissue protein kinases also represent potential targets for future antimicrobial compounds for decreasing Salmonella loads in the intestines of food animals before going to market.

Upregulation of NRAMP1 mRNA confirms its role in enhanced host immunity in post-artificial infections of Salmonella enteritidis in chicks

1. Salmonella enteritidis (SE) is reported as the most common food-borne pathogen transmitted through poultry products. The natural resistance-associated macrophage protein 1 (NRAMP1) is a candidate gene associated with SE-mediated immune response and is related to the phagocytosis of SE. In this study, the classical single-nucleotide polymorphism (SNP) G2357A in exon 8 of the NRAMP1 gene was detected. The expression of NRAMP1 mRNA was first investigated in heterophil granulocytes and spleen in chicks from two different Chinese native breeds at 1, 3 and 10 d post-infection. In addition, the association with the effect of SE challenge was identified. 2. The G2357A SNP showed no significant association with Salmonella natural infection in birds from two different Chinese native breeds. 3. The upregulation of NRAMP1 mRNA in heterophils and spleen was involved in the response to pathogenic SE colonisation during the acute infection period in chicks. The results suggest that genetics, age, gender and interactions among these factors play important roles in the modulation of NRAMP1 mRNA expression and copy number by SE-mediated immune response in different Chinese chickens. 4. In conclusion, the enhancement of host immunity mediated by the upregulation of NRAMP1 mRNA in heterophil granulocytes and spleen might be more obvious and earlier in the chicks resistant to infections with SE than in susceptible chicks.

Effect of Salmonella infection on cecal tonsil regulatory T cell properties in chickens

Two studies were conducted to study regulatory T cell [Treg (CD4⁺CD25⁺)] properties during the establishment of a persistent intestinal infection in broiler chickens. Four-day-old broiler chicks were orally gavaged with 5 × 10⁶ CFU/mL Salmonella enteritidis (S. enteritidis) or sterile PBS (control). Samples were collected at 4, 7, 10, and 14 d postinfection. There was a significant (P < 0.05) increase in the number of CD4⁺CD25⁺ cells by d 4 postinfection that increased steadily throughout the course of the 14-d infection, whereas the number of CD4⁺CD25⁺ cells in the noninfected controls remained steady throughout the study. CD4⁺CD25⁺ cells from cecal tonsils of S. enteritidis-infected birds had a higher (P < 0.05) IL-10 mRNA content than CD4⁺CD25⁺ cells from the noninfected controls at all time-points studied. The amount of IL-2 mRNA content in the cecal tonsil CD4⁺CD25⁻ cells from the infected birds did not differ (P > 0.05) when compared to that of noninfected control birds. At a lower effector/responder cell ratio of 0.25:1, CD4⁺CD25⁺ cells from cecal tonsils of Salmonella-infected birds suppressed T cell proliferation at d 7 and 14 post-S. enteritidis infection, while CD4⁺CD25⁺ cells from noninfected control groups did not suppress T cell proliferation. In the second studu, 1-day-old chickens were orally gavaged with PBS (control) or 1.25 × 10⁸ CFU/bird S. enteritidis. At 7 and 21 d post-Salmonella infection, CD25⁺ cells collected from cecal tonsils of S. enteritidis-infected birds and restimulated in vitro with Salmonella antigen had higher (P < 0.05) IL-10 mRNA content compared to those in the control group. Spleen CD4⁺CD25⁺, CD4⁺, and CD8⁺ cell percentage did not differ (P > 0.05) between the Salmonella-infected and control birds. In conclusion, a persistent intestinal S. enteritidis infection increased the Treg percentage, suppressive properties, and IL-10 mRNA amounts in the cecal tonsils of broiler birds.

Salmonella Enteritidis infection slows steroidogenesis and impedes cell growth in hen granulosa cells

Infection by Salmonella Enteritidis (SE) causes decreased egg production in laying hens. Immunoresponse, steroidogenesis, and cell proliferation by chicken granulosa cells (cGCs) are of particular interest because these changes are involved in follicular growth, atresia, and ovulation. To elucidate the possible mechanisms underlying these changes, transcriptional alterations in cGCs at distinct stages of follicular maturity were studied. Luteinizing hormone (LH)-and follicle-stimulating hormone (FSH) were applied to the cGCs isolated from hierarchical and prehierarchical follicles, respectively, to imitate the effects of gonadotropin during in vitro SE infection. Results showed that the expression of Toll-like receptor 15 was dependent on the follicular maturity, with mature cells having a more significant and progressively stronger immunoresponse. Attenuated responses to LH and FSH as well as retardant steroidogenesis due to down-regulated LH receptor, FSH receptor, and the P450 side-chain cleavage system were observed and may have led to delayed hierarchical follicular growth. Deteriorated cell viability of prehierarchical follicles may occur, as the proliferation of stimulator heparin-binding epidermal growth factor was reduced significantly. Furthermore, the infection led to a higher probability of cGCs from the smaller follicles undergoing apoptosis than those from F1 follicles. Collectively, the data provide evidence of a tendency toward pathogen elimination in F1 follicles by induction of a strong immune response and cell apoptosis in smaller follicles to avoid bacterial transovarian infection. It is our speculation that slowed steroidogenesis and impeded follicular growth may play essential roles in decreased ovulation rate as well as further decreased egg production during SE infection.

Cytokines Expression and Nitric Oxide Production under Induced Infection to Salmonella Typhimurium in Chicken Lines Divergently Selected for Cutaneous Hypersensitivity

In the present study, the impact of Salmonella Typhimurium on cell-mediated immunity (CMI) was investigated in 5 week-old immuno divergent broiler lines selected for the high and low response to phytohemagglutinin-P. The immune response was assessed in peripheral-blood mononuclear cells (PBMCs) induced with Salmonella Typhimurium at different time intervals (0 h, 0.5 h, 2 h, 4 h, 6 h, 12 h and 24 h). The differential mRNA expression patterns of IFN-γ, IL-2 and iNOS were evaluated by quantitative real time PCR. In-vitro production of nitric oxide (NO) was also estimated in the culture supernatant and correlated with iNOS mRNA expression. Present study showed higher production of NO in the high cell-mediated line (HCMI) as compared to the low cell-mediated line (LCMI) upon stimulation with Salmonella Typhimurium. Correspondingly, higher mRNA expression of iNOS and IFN-γ were observed in high response birds (HCMI); but IL-2 was down regulated in this line compared to the low response birds (LCMI). Significantly (p<0.05) higher expression of iNOS, IFN-γ and higher production of NO in high line indicated that the selection for PHA-P response might be employed for increasing the immune competence against Salmonella Typhimurium in chicken flocks.

Selection for pro-inflammatory mediators yields chickens with increased resistance against Salmonella enterica serovar Enteritidis

Salmonella is a leading cause of foodborne illness and can be transmitted through consumption of contaminated poultry; therefore, increasing a flock's natural resistance to Salmonella could improve food safety. Previously, we characterized the heterophil-mediated innate immune response of 2 parental broiler lines and F1 reciprocal crosses and showed that increased heterophil function and expression of pro-inflammatory mediators corresponds with increased resistance against diverse pathogens. A preliminary selection trial showed that individual sires had varying inherent levels of pro-inflammatory mediators and selection based on a high or low phenotype was passed onto progeny. Based on these results, we hypothesized selection of broilers for higher levels of the pro-inflammatory mediators IL-6, CXCLi2, and CCLi2 would produce progeny with increased resistance against Salmonella Enteritidis. Peripheral blood leukocytes were isolated from 75 commercial broiler sires, screened, and 10 naturally high and low expressing sires were selected and mated to randomly selected dams to produce the first generation of "high" and "low" progeny. The mRNA expression of CXCLi2 and CCLi2 were significantly (P ≤ 0.02) higher in the high progeny and were more resistant to liver and spleen organ invasion by Salmonella Enteritidis compared with low progeny. Production of the second generation yielded progeny that had differences (P ≤ 0.03) in all 3 mediators and further improved resistance against Salmonella Enteritidis. Feed conversion ratio and percent breast meat yield were calculated and were equal, whereas the high birds weighed slightly, but significantly, less than the low birds. These data clearly demonstrate that selection based on a higher phenotype of key pro-inflammatory mediators is a novel means to produce broilers that are naturally more resistant to Salmonella, one of the most important foodborne pathogens affecting the poultry industry.

Susceptibility to Salmonella carrier-state: a possible Th2 response in susceptible chicks

Infection of chicken with Salmonella may lead to a carrier-state characterized by the persistence of bacteria in the ceca for a long period of time and result in their excretion in feces. This excretion is the source of contamination of their congeners and food. During infection, enterocytes are the primary target cells for Salmonella, the producers of soluble factors which launch immune response and cells which are reciprocally responsive to surrounding immune cells. This study used microarrays to compare the gene expression profile during carrier-state of enterocytes purified from infected and control chicks which are either resistant or susceptible to Salmonella Enteritidis carrier-state. In total, we identified 271 genes significantly differentially expressed with an absolute fold change greater than 1.5. A global analysis determined interaction networks between differentially regulated genes. Using an a priori approach, our analyses focused on differentially expressed genes which were transcriptionally linked to cytokines playing a major role in the fate of the immune response. The expression of genes transcriptionally linked to type I interferon and TGF-β was down-regulated in infected chicks from both lines. Gene expression linked to the Th1 axis suggests the latter is inhibited in both lines. Finally, the expression of genes linked to IL-4, IL-5 and IL-13 indicates that susceptibility to carrier-state could be associated with a Th2 bias. Overall, these results highlight that the response to Salmonella during the acute phase and carrier-state is different and that enterocytes play a central role in this response.

Antibody response toSalmonella: its induction and role in protection against avian enteric salmonellosis

Human enteritis resulting from the consumption of poultry products contaminated with serovars of Salmonella enterica remains a major public-health concern. Reducing food contamination by preventing or controlling infection in the chicken during rearing is an attractive solution. An accurate understanding of the mechanisms of immunity to Salmonella infection in the chicken will help to focus the development of vaccines for birds and prevent contaminated products from entering the human food chain. Infection is primarily restricted to the intestinal lumen when chickens are infected with S. enterica serovars Typhimurium or Enteritidis, where they persist for many weeks. High titers of Salmonella-specific antibodies are observed following infection and demonstrate a high degree of cross-reactivity against other serovars. However, depletion of B cells and, therefore, removal of the capacity for antibody production in the chicken does not exacerbate the infection following either primary or secondary challenge.

In vitro rapid clearance of infectious bursal disease virus in peripheral blood mononuclear cells of chicken lines divergent for antibody response might be related to the enhanced expression of proinflammatory cytokines

Infectious bursal disease (IBD) is an acute and highly contagious viral disease of young chickens caused by infectious bursal disease virus (IBDV). An effective way to control IBDV would be to breed chickens with a reduced susceptibility to IBDV infection. In the present work, we used chickens selected for high and low specific responses to sheep red blood cells (SRBC) (H and L, respectively) to assess the susceptibility of differential immune competent animals to IBDV infection. The peripheral blood mononuclear cells (PBMCs) of high SRBC line (HL) and low SRBC line (LL) were infected with IBDV and viral RNA loads were determined at different time post-IBDV infection. Chicken orthologues of the T helper 1 (Th1) cytokines, interferon-γ (IFN-γ) and interleukin-2 (IL-2); a Th2 cytokine, IL-10; a pro inflammatory cytokine, IL-6; the CCL chemokines, chCCLi2, chCCLi4 and chCCLi7; colony stimulating factor, GM-CSF; and a anti-inflammatory cytokine, transforming growth factor β-2 (TGFβ-2) were quantified. The expression of chCCLi2, chCCLi4 and chCCLi7 was significantly higher in L line as compared to H line. However, in H line the viral RNA loads were significantly lower than in L line. Therefore, the upregulated chemokines might be associated with the susceptibility to IBDV. The expression of IFN-γ, IL-2 and IL-6 was significantly higher in H line as compared to L line. We assume that the higher proinflammatory cytokines expression in H line might be related to the rapid clearance of virus from PBMCs. Significantly higher levels of IL-10 and TGFβ-2 mRNAs in L line might be related to the pathogenesis of IBDV. In conclusion, selection for antibody responses appears to influence the expression profiles of chemokines and cytokines against IBDV. Further, the selection for high SRBC response might improve the immuno-competence of chickens against IBDV.

Avian CD4(+)CD25(+) regulatory T cells: properties and therapeutic applications

Regulatory T cells (Tregs) are a subset of T cells that specialize in immune suppression. CD4(+)CD25(+)FoxP3(+) T cells have been characterized as Tregs and extensively studied in mammals. In the absence of a putative FoxP3 ortholog in avians, CD4(+)CD25(+) cells is characterized as Tregs in avians. Avian CD4(+)CD25(+) cells produce high amounts of IL-10, TGF-β, CTLA-4, and LAG-3 mRNA; lack IL-2 mRNA; and suppress T cell proliferation in vitro through both contact-dependent and -independent pathways. Depleting avian CD4(+)CD25(+) cells increases the proliferation of, IL-2 amount, and IFNγ mRNA amount of CD4(+)CD25(-) cells. Avian CD4(+)CD25(+) cells lose their suppressive properties immediately after inflammation and acquire supersuppressive properties once inflammation subsides. Although Treg activity could be beneficial to the host, Tregs simultaneously inhibit host immunity and cause persistent infections of certain pathogens. Therapy targeted toward alleviating Treg mediated immune suppression can improve host immunity against those persistent pathogens and benefit poultry production.

Genetic differ in TLR4 gene polymorphisms and expression involved in Salmonella natural and artificial infection respectively in Chinese native chicken breeds

Salmonella enteritidis (SE) is a foodborne pathogen that negatively affects both animal and human health. Genetic variations in response to pathogenic SE colonization or to SE vaccination were measured in chicken resource populations. Toll-like receptor 4 (TLR4) is part of a group of evolutionarily conserved pattern recognition receptors involved in the activation of the immune system in response to various pathogens and in the innate defense against infection. In this study, TLR4 was investigated the association of TLR4 gene polymorphisms with Salmonella natural infection situation of birds from two distinct Chinese genetic breeds. One SNP G1894C in the second intron of chicken TLR4 (chTLR4) was scanned in the two hens breed, which showed significant association with Salmonella natural infection situation (P<0.05). Genetic variations in response to pathogenic SE colonization also existed in distinct Chinese chicken resource population. In this study, mRNA expression of TLR4 was detected to investigate the association with the effect of artificial SE challenge in heterophil granulocytes and spleen of chicks from two distinct Chinese genetic breeds at 1, 3 and 10 day post-infection during the acute infection period. It clearly showed that young chicks' response to SE infection was regulated by TLR4 mRNA expression. The results suggest that genetics, time, gender, and interactions among these factors, play important roles in TLR4 mRNA basic values and copies modulation of SE mediated immune response in distinct Chinese chickens.

Infection cycle of Salmonella enterica serovar Enteritidis in latent carrier mice 1The work was carried out at the Microbial Biotechnology Laboratory of Universidade Estadual de Santa Cruz, Ilhéus, Bahia State, Brazil

This work reports the distribution of an oral dose of Salmonella enterica serovar Enteritidis (SE) in C57Bl/6-Bcgr mice, to study its pathogenesis in a latent carrier animal. Mice orally inoculated with a high dose of SE developed a latent infection characterized by the absence of clinical symptoms in which the cecum is functioning as a “strategic site” of SE proliferation, releasing bacteria into feces intermittently over the 4-week study. A sequence of disruptions occurred in the small intestine at 1 day postinculation (PI). The microvilli exhibited different degrees of degeneration, which were reversible as the cells became vacuolated. From 2 days PI, SE was detected in the mononuclear phagocytic system, and an exponential growth of the remaining bacteria in tissues was observed until 4 days PI. The production of interferon gamma from 3 days PI is restricting the SE growth, and a plateau phase was observed from 4 to 15 days PI. A recurrence of the bacterial growth in tissue occurred from 15 to 28 days PI, especially in the cecum. Increasing our knowledge about the host–pathogen interaction of adapted pathogens with the ability to develop latency is essential for the development of an efficient strategy for Salmonella control.

Quantification of interferon, interleukin, and Toll-like receptor 7 mRNA in quail splenocytes using real-time PCR

Japanese quail (Coturnix japonica) are farmed worldwide as poultry. Quail have been used as experimental animals in various scientific fields, but their immunological characteristics have not been well characterized. In this study, to develop a method for analyzing the innate immune response of quail to infectious pathogens, we determined the nucleotide sequences of major interleukins (IL) and Toll-like receptor (TLR)-7 of quail and developed quantitative real-time PCR assays. The nucleotide sequences of quail IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12a, IL-12b, IL-13, IL-18, and TLR-7 were determined based on the sequences of the chicken genes. Specific primers for each of these genes and previously reported interferon (IFN)-α, IFN-γ, and IL-2 genes were designed for quantitative real-time PCR. Standard curves for quantification were established using serial dilutions of external standard plasmids containing real-time PCR products. Then, real-time PCR was performed to monitor the kinetics of quail immune-related gene expression induced in splenocytes stimulated with concanavalin A. After amplification, the r(2) values of the standard curves for all target genes were above 0.980. Melting analysis of real-time PCR revealed specific amplification of each gene that could be visualized clearly as a single peak of melting temperature in a melt peak chart. These data show that the mRNA expressions of quail immune-related genes can be accurately quantified using this real-time PCR assay. In this study, we showed the nucleotide sequences of several quail cytokine mRNA and constructed the quantitative real-time PCR for quail immune-related genes.

Oral administration of a combination of select lactic acid bacteria strains to reduce the Salmonella invasion and inflammation of broiler chicks

One-day-old chicks are susceptible to infection by strains of Salmonella enterica subspecies. Because multistrain probiotics are suggested to be more effective than monostrain probiotics due to the additive and synergistic effects, in this study, we prepared a multistrain formula A (MFA) consisting of 4 lactic acid bacteria (LAB) strains selected by enhancing the TNF-α production for mouse macrophage 264.7 cells. The antagonistic effect of this MFA against the cecal colonization, viscera invasiveness, as well as the inflammation of 1-d-old chicks challenged with Salmonella Typhimurium were then assayed. One-day-old chicks were fed with MFA from d 1 to d 3, and on d 4, chicks were challenged with Salmonella Typhimurium (200 μL, 10(6) cfu/mL). The livers, spleens, and cecal tonsils of chicks were then removed on d 3 and 6 postinfection. Compared with the multistrain formula B (MFB) which consisted of LAB strains selected at random, the efficacy of MFA to reduce the Salmonella counts recovered from the cecal tonsils, spleens, and livers of chicks were significantly higher. Moreover, when the levels of proinflammatory cytokines, such as IL-1β, IL-6, interferon (IFN)-γ, and anti-inflmmatory cytokine, that is, IL-10, in cecal tonsils were measured by reverse-transcription real-time quantitative PCR; it was found that chicks fed with MFA for 3 d had lower levels of IL-1β, IL-6, IFN-γ and a higher level of IL-10 in the cecal tonsils of chicks as compared with those of the chicks fed with MFB or without LAB. These results suggest that multistrain probiotics consisting of LAB strains selected by immunomodulatory activity and adherence are more effective than those consisting of strains selected at random in antagonistic effect against Salmonella colonization, invasion, and the induced inflammation.