Chicken cecum immune response to Salmonella enterica serovars of different levels of invasiveness

Compensatory mechanisms in γδ T cell-deficient chickens following Salmonella infection

Avian γδ T lymphocytes are highly abundant in the intestinal mucosa and play a critical role in immune defense against infectious diseases in chickens. However, their specific contributions to infection control remain poorly understood. To investigate the role of γδ T cells and their possible compensation, we studied wild-type and γδ T cell knockout chickens following infection with Salmonella Enteritidis. Bacterial loads in the liver, cecal content, and cecal wall were quantified. Immune cell populations in blood, spleen, and cecum were analyzed using flow cytometry. Immune gene transcription in sorted γδ (TCR1+) and TCR1- cell subsets as well as cecal tissue was measured by RT-qPCR. Strikingly, chickens lacking γδ T cells had significantly higher bacterial loads in the liver and more extensive Salmonella invasion in the cecal wall during the early stages of infection compared to wild-type birds. In blood, infected γδ T cell knockout chickens displayed a significantly increased percentage of CD25+ NK-like cells. In both blood and tissue, infected wild-type chickens demonstrated an increased absolute number of CD8αα+hi γδ T cells (CD4-). Conversely, γδ T cell knockout chickens exhibited an augmented cell count of a CD8αα+hiCD4-TCR1- cell population after infection, which might include αβ T cells. At 7 days post infection (dpi), gene expression analysis revealed elevated transcription of the activation marker IL-2Rα and proinflammatory cytokines (IL-17A, IFN-γ) in CD8αα+hiCD4-TCR1- cells from γδ T cell knockout chickens compared to CD8αα+hi γδ T cells from wild-type birds. By 12 dpi, these differences diminished as transcription levels increased in γδ T cells of wild-type animals. Our findings demonstrate that γδ T cells play a role in early immune protection against Salmonella Enteritidis infection in chickens. In later stages of the infection, the γδ T cells and their functions appear to be replaced by other cells.

Age of challenge is important in Salmonella Enteritidis studies in pullets and hens: a systematic review

Nontyphoidal serovars of Salmonella enterica subsp enterica frequently colonize the intestinal tracts of chickens, creating risks of contamination of meat and egg food products. These serovars seldom cause disease in chickens over 3 weeks of age. Colonization is generally transient but can continue to circulate in a flock for many months. Vaccination of breeders and layers is the most effective method of control of infections with serovars Enteritidis and Typhimurium, and the development of these vaccines or other preventative treatments requires challenge studies to demonstrate efficacy. However, establishing a successful challenge model where the control birds are colonized to a sufficient extent to be able to demonstrate a statistically significant reduction from the vaccine or treatment is problematic. A meta-analysis of published S. Enteritidis challenge studies was performed to pursue the best challenge model conditions that provide consistent control colonization outcomes. Challenge at sexual maturity was significantly more effective in achieving at least 80% colonization of control hens.RESEARCH HIGHLIGHTSSalmonella challenge chicken models do not always achieve high colonization levels in controls.The age of hen is important in achieving good caecal colonization.Challenge around sexual maturity provides the best control colonization outcome.A challenge dose rate of 105 CFU/ bird is adequate in birds under 30 weeks of age.

Temporal transcriptome profiling in the response to Salmonella enterica serovar enteritidis infection in chicken cecum

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a common zoonotic pathogen that not only causes gastroenteritis or death of livestock and poultry but also poses a serious threat to human health, causing severe economic losses to the poultry industry and society. Herein, RNA-sequencing (RNA-seq) was used to analyze the transcriptome variation of chicken cecum at four different time points (1, 3, 7, and 14 days) following S. Enteritidis infection. There were 529, 1477, 476, and 432 differentially expressed genes (DEGs) in the cecum at four different days post-infection (dpi), respectively. The DEGs were significantly enriched in various immune-related pathways on 3 dpi and 7 dpi, such as cytokine-cytokine-receptor interaction and Toll-like receptor signaling pathway. DEGs were significantly enriched in several metabolic pathways on 14 dpi. Gene ontology (GO) enrichment of DEGs showed that up-regulated genes were significantly enriched in immune-related terms on 3 and 7 dpi. On 14 dpi, up-regulated genes were mainly enriched in the signaling-related terms, while the down-regulated genes were primarily enriched in the metabolic-related terms. Based on weighted gene co-expression network analysis (WGCNA), the key modules related to energy, non-coding processes, immunity, and development-related functions were identified at 1, 3, 7, and 14 dpi, respectively, and 5, 8, 6, and 5 hub genes were screened out, respectively. This study demonstrated that the chicken cecal transcriptome regulation responding to S. Enteritidis infection is time-dependent. The regulation of S. Enteritidis infection in chickens is coordinated by multiple systems, mainly involving immunity, metabolism, and signal transduction. Both 3 and 7 dpi are key time points for immune response. As the infection progresses, metabolism-related pathways were increasingly identified. This change reflects the dynamic adjustment between immune response and metabolism in Jining Bairi chickens following S. Enteritidis infection. These results suggested that starting from 3 dpi, the chickens gradually transition from an immune response triggered by S. Enteritidis infection to a state where they adapt to the infection by modulating their metabolism.

A temporary cholesterol-rich diet and bacterial extracellular matrix factors favor Salmonella spp. biofilm formation in the cecum

Asymptomatic chronic carriers occur in approximately 5% of humans infected with Salmonella enterica serovar Typhi (S. Typhi) and represent a critical reservoir for bacterial dissemination. While chronic carriage primarily occurs in the gallbladder (GB) through biofilms on gallstones, additional anatomic sites have been suggested that could also harbor Salmonella. S. Typhimurium, orally infected 129 × 1/SvJ mice were pre-treated with a cholesterol-rich diet as a gallstone model for chronic carriage. We observed S. Typhimurium in feces and the cecum during early and persistent infection. Furthermore, bacterial biofilm-like aggregates were associated with the cecum epithelium at 7 and 21 days post-infection (DPI) in mice on a lithogenic diet (Ld) and correlated with an increase in cecal cholesterol at 21 DPI. Salmonella's extracellular matrix (ECM) was demonstrated as important in colonizing the cecum, as survival and aggregate formation significantly decreased when mice were infected with a quadruple ECM mutant strain. Gallbladder Salmonella counts were low at 36 DPI while cecal Salmonella were high, suggesting that gallbladder colonization was likely not responsible for the high cecal burden. All cecum phenotypes were significantly diminished in mice fed a normal diet (Nd). Finally, we examined the capability of S. Typhi to colonize the cecum and showed S. Typhi in feces and in aggregates in the cecum up to 7 DPI, with slightly higher counts in mice fed a Ld compared to Nd. Our findings suggest that the cecum, particularly under cholesterol-rich conditions, serves as an adaptative niche for Salmonella spp. aggregates/biofilms and is a putative site for long-term infection.IMPORTANCETyphoid fever is a systemic infectious disease triggered by the gastrointestinal dissemination of Salmonella Typhi and Paratyphi in humans. Three to five percent of infected individuals become chronic carriers, a state in which gallstone biofilm formation facilitates spread of the bacteria in feces. Notably, surgical removal of the gallbladder (GB) in some chronic carriers (22%) does not guarantee the elimination of the bacteria, and the rationale for this remains poorly understood. This study is significant as it explores other tissues associated with the chronic carrier state. It highlights not only a cholesterol-rich diet as an important etiological factor for Salmonella colonization but also identifies the cecum as a crucial tissue promoting fecal shedding. Additionally, we determined that biofilm matrix components of Salmonella are key factors contributing to these effects. A greater understanding of these mechanisms will allow the formulation of new therapeutic strategies specifically targeted at preventing typhoid fever dissemination from chronic carriers.

A Two Bacteriocinogenic Ligilactobacillus Strain Association Inhibits Growth, Adhesion, and Invasion of Salmonella in a Simulated Chicken Gut Environment

In this study, we aimed to develop a protective probiotic coculture to inhibit the growth of Salmonella enterica serovar Typhimurium in the simulated chicken gut environment. Bacterial strains were isolated from the digestive mucosa of broilers and screened in vitro against Salmonella Typhimurium ATCC 14028. A biocompatibility coculture test was performed, which identified two biocompatible strains, Ligilactobacillus salivarius UO.C109 and Ligilactobacillus saerimneri UO.C121 with high inhibitory activity against Salmonella. The cell-free supernatant (CFS) of the selected isolates exhibited dose-dependent effects, and the inhibitory agents were confirmed to be proteinaceous by enzymatic and thermal treatments. Proteome and genome analyses revealed the presence of known bacteriocins in the CFS of L. salivarius UO.C109, but unknown for L. saerimneri UO.C121. The addition of these selected probiotic candidates altered the bacterial community structure, increased the diversity of the chicken gut microbiota challenged with Salmonella, and significantly reduced the abundances of Enterobacteriaceae, Parasutterlla, Phascolarctobacterium, Enterococcus, and Megamonas. It also modulated microbiome production of short-chain fatty acids (SCFAs) with increased levels of acetic and propionic acids after 12 and 24 h of incubation compared to the microbiome challenged with S. Typhimurium. Furthermore, the selected probiotic candidates reduced the adhesion and invasion of Salmonella to Caco-2 cells by 37-39% and 51%, respectively, after 3 h of incubation, compared to the control. These results suggest that the developed coculture probiotic strains has protective activity and could be an effective strategy to control Salmonella infections in poultry.

Dynamic Changes in the Intraepithelial Lymphocyte Numbers Following Salmonella Typhimurium Infection in Broiler Chickens

At day 21 of age, Ross-308 broilers were orally gavaged with 7.5 × 106 CFU/mL S. Typhimurium (n = 30), and another 30 birds were kept as the control. The body weight of birds was recorded on days 0, 2, 7, and 14 days post-infection (dpi) to calculate body weight gains (BWGs). At each time point, seven birds per group were euthanized for sample collection to acquire IELs and lymphocytes from the ileum and spleen for flow cytometric analysis. A reduction in BWGs of the infected groups compared to the control group was observed only at 2 dpi. Additionally, there were no changes in the expression of IFN-γ, IL-1β, and TNF-α in the ileum at 2 and 7 dpi. The number of IELs increased significantly following Salmonella infection in the ileum at 2 and 7 dpi without any changes in spleen lymphocytes. The increase in the total number of IELs was derived from the elevated numbers of conventional CD8αβ+TCRαβ+ and natural IEL populations (CD4-CD8-TCRαβ+, CD8αα+TCRαβ+, TCRγδ+, non-T cells (TCRneg, and iCD8α cells)). The increase in regulatory IELs and the stable expression of proinflammatory cytokine genes during the first week of infection suggests the potential role of IELs in modulating intestinal inflammation.

Emergence of Salmonella Infantis carrying the pESI-like plasmid from eggs in egg grading and packing plants in Korea

The plasmid of emerging S. Infantis (pESI) or pESI-like plasmid in Salmonella enterica Infantis are consistently reported in poultry and humans worldwide. However, there has been limited research on these plasmids of S. Infantis isolated from eggs. Therefore, this study aimed to analyze the prevalence and characteristics of S. Infantis carrying the pESI-like plasmid from eggs in egg grading and packing plants. In this study, the pESI-like plasmid was only detected in 18 (78.3%) of 23 S. Infantis isolates, and it was absent in the other 9 Salmonella serovars. In particular, S. Infantis isolates carrying the pESI-like plasmid showed the significantly higher resistance to β-lactams, phenicols, cephams, aminoglycosides, quinolones, sulfonamides, and tetracyclines than Salmonella isolates without the pESI-like plasmid (p < 0.05). Moreover, all S. Infantis isolates carrying the pESI-like plasmid were identified as extended-spectrum β-lactamase (ESBL) producer, harboring the blaCTX-M-65 and blaTEM-1 genes, and carried non-β-lactamase resistance genes (ant(3'')-Ia, aph(4)-Ia, aac(3)-IVa, aph(3')-Ic, sul1, tetA, dfrA14, and floR) against five antimicrobial classes. However, all isolates without the pESI-like plasmid only carried the blaTEM-1 gene among the β-lactamase genes, and either had no non-β-lactamase resistance genes or harbored non-β-lactamase resistance genes against one or two antimicrobial classes. Furthermore, all S. Infantis isolates carrying the pESI-like plasmid carried class 1 and 2 integrons and the aadA1 gene cassette, but none of the other isolates without the pESI-like plasmid harbored integrons. In particular, D87Y substitution in the gyrA gene and IncP replicon type were observed in all the S. Infantis isolates carrying the pESI-like plasmid but not in the S. Infantis isolates without the pESI-like plasmid. The distribution of pulsotypes between pESI-positive and pESI-negative S. Infantis isolates was clearly distinguished, but all S. Infantis isolates were classified as sequence type 32, regardless of whether they carried the pESI-like plasmid. This study is the first to report the characteristics of S. Infantis carrying the pESI-like plasmid isolated from eggs and can provide valuable information for formulating strategies to control the spread of Salmonella in the egg industry worldwide.

Structure and biological activity in vitro of Flagellin and its mutants from Escherichia coli Nissle 1917

Bacterial flagellin is a potent immunomodulatory agent. Previously, we successfully obtained flagellin from Escherichia coli Nissle 1917 (FliCEcN) and constructed two mutants with varying degrees of deletion in its highly variable regions (HVRs). We found that there was a difference in immune stimulation levels between the two mutants, with the mutant lacking the D2-D3 domain pair of FliCEcN having a better adjuvant effect. Therefore, this study further analyzed the structural characteristics of the aforementioned FliCEcN and its two mutants and measured their levels of Caco-2 cell stimulation to explore the impact of different domains in the HVRs of FliCEcN on its structure and immune efficacy. This study utilized AlphaFold2, SERS (Surface-enhanced Raman spectroscopy), and CD (circular dichroism) techniques to analyze the structural characteristics of FliCEcN and its mutants, FliCΔ174-506 and FliCΔ274-406, and tested their immune effects by stimulating Caco-2 cells in vitro. The results indicate that the D2 and D3 domains of FliCEcN have more complex interactions compared to the D1-D2 domain pair., and these domains also play a role in molecular docking with TLR5 (Toll-like receptor 5). Furthermore, FliCΔ274-406 has more missing side chain and characteristic amino acid peaks than FliCΔ174-506. The FliCEcN group was found to stimulate higher levels of IL-10 (interleukin 10) secretion, while the FliCΔ174-506 and FliCΔ274-406 groups had higher levels of IL-6 (interleukin 6) and TNF-α (tumor necrosis factor-α) secretion. In summary, the deletion of different domains in the HVRs of FliCEcN affects its structural characteristics, its interaction with TLR5, and the secretion of immune factors by Caco-2 cells.

Emergence of Salmonella Infantis carrying the pESI megaplasmid in commercial farms of five major integrated broiler operations in Korea

Considering Salmonella transmission occurs through several routes in integrated broiler operations, control of nontyphoidal Salmonella in commercial farms is essential. This study aimed to compare the distribution of persistent Salmonella serovars in environments and dead chickens between 5 major integrated broiler operations in Korea. The prevalence of Salmonella-positive farms in dust prior to placement by operations was 0 to 25%, but the prevalence in dust and feces at the time of depletion was increased to 16.7 to 41.7% and 16.7 to 66.7%, respectively. Moreover, the prevalence of farms with Salmonella in chickens that died within 1 week old and at 4 to 5 weeks old ranged from 8.3 to 58.3% and 16.7 to 41.7%, respectively. The prevalence of Salmonella enterica serovar Infantis-positive farms in dust prior to placement and in chickens that died within 1 week old was 5.2 and 3.4%, respectively, but the prevalence in dust and feces at the time of depletion and in chickens that died at 4 to 5 weeks old was significantly increased to 27.6, 41.4, and 20.7%, respectively (P < 0.05). Interestingly, the plasmid of emerging S. Infantis (pESI) was only identified in S. Infantis, and the prevalence of multidrug-resistance was significantly higher in pESI-positive S. Infantis (99.2%) than in pESI-negative S. Infantis (6.7%) (P < 0.05). The distribution of pulsotypes between pESI-positive and pESI-negative S. Infantis were varied, but a majority of S. Infantis were clustered only 2 pulsotypes. Moreover, pESI-positive S. Infantis harbored more virulence factors than pESI-negative S. Infantis. This study is the first report on characteristics of S. Infantis carrying the pESI plasmid in commercial broiler farms in Korea.

Effects of Salmonella Outer Membrane Vesicles on Intestinal Microbiota and Intestinal Barrier Function

Salmonella enterica is one of the most important zoonotic pathogens causing foodborne gastroenteritis worldwide. Outer membrane vesicles (OMVs) are lipid-bilayer vesicles produced by Gram-negative bacteria, which contain biologically active components. We hypothesized that OMVs are an important weapon of S. enterica to initiate enteric diseases pathologies. In this study, the effects of S. enterica OMVs (SeOMVs) on intestinal microbiota and intestinal barrier function were investigated. In vitro fecal culture experiments showed that alpha diversity indexes and microbiota composition were altered by SeOMV supplementation. SeOMV supplementation showed an increase of pH, a decrease of OD630 and total short chain fatty acid (SCFA) concentrations. In vitro IPEC-J2 cells culture experiments showed that SeOMV supplementation did not affect the IPEC-J2 cell viability and the indicated genes expression. In vivo experiments in mice showed that SeOMVs had adverse effects on average daily gain (p < 0.05) and feed:gain ratio (p < 0.05), and had a tendency to decrease the final body weight (p = 0.073) in mice. SeOMV administration decreased serum interleukin-10 level (p < 0.05), decreased the relative abundance of bacteria belonging to the genera BacC-u-018 and Akkermansia (p < 0.05). Furthermore, SeOMV administration damaged the ileum mucosa (p < 0.05). These findings suggest that SeOMVs play an important role in the activation of intestinal inflammatory response induced by S. enterica, and downregulation of SCFA-producing bacteria is a possible mechanism.

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

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

Salmonella Gallinarum mgtC mutant shows a delayed fowl typhoid progression in chicken

Salmonella Gallinarum (SG) provokes fowl typhoid, an infectious disease of acute clinical course that affects gallinaceous of any age and leads to high mortality rates. During the typhoid-like systemic infection of S. Typhimurium (STM) in mice, the bacterium expresses the mgtC gene, which is encoded in the Salmonella Pathogenecity Island - 3 (SPI-3). In this serovar, the function is linked to bacterial replication within macrophages, and its absence attenuates the pathogen. We hypothesized that deleting mgtC from SG genome would alter the microorganism pathogenicity in susceptible commercial poultry in a similar manner. Thus, the present study sought to elucidate the importance of mgtC on SG pathogenicity. For this, a mgtC-mutant lacking S. Gallinarum mutant was constructed (SG ΔmgtC). Its ability to replicate in medium that mimicries the mgtC-related intracellular environment of macrophages as well as in primary macrophages from chicken was evaluated. Moreover, the infection of susceptible chickens was performed to elucidate its pathogenicity and the elicited immune responses by measuring key interleukins by qRT-PCR and the population of macrophages and lymphocytes T CD4+ and CD8+ by means of immunohistochemistry. It was observed that mgtC was required for S. Gallinarum replication in acidified low-Mg2+ media and survival within macrophages. However, unlike its requirement for initial phase of STM infection in mice, lower bacterial counts were only observed at the late stage of macrophage infection without affecting the citotoxicity. Experiments showed that knocking-out the mgtC gene neither altered bacterial uptake by macrophages nor affects bacterial counts in liver and spleen and total chicken mortality. However, plotting a survival curve and analyzing the clinical-pathologic conditions, it was observed a slower progression of the disease in chickens infected by SG ΔmgtC compared to those challenged by the wild-type strain. Furthermore, the mRNA expression of IFN-γ and LITAF were similar between the infected chickens, but higher than in the uninfected group. The same was observed in macrophages and lymphocytes T CD4+ populations. On the other hand, the presence of lymphocytes T CD8+ was increased in the initial phase of the disease provoked by the wild-type strain over the mutant strain. We concluded that the role of mgtC in Fowl Typhoid in susceptible chickens differs from the role in typhoid-like infections in mammals. Thus, the deletion of mgtC gene from S. Gallinarum genome does not affect the overall pathogenicity, but slightly alters the pathogenesis.

Transcriptional responses of cytokines, immunoglobulin A, and nitric oxide genes in 1-day-old chicks post Salmonella typhimurium infection: An experimental study

Background

Salmonella has become one of the hazards prevalent foodborne pathogens causing different diseases in chickens. However, Salmonella typhimurium (ST), a nonhost-specific serovar, is a major avian agent that causes severe disturbance in young chicken wellness.

Aim

The occurrence of Salmonella in chickens and their antimicrobial resistance were explored in this study. In addition, the immune response of 1-day-old broiler chicks, against multidrug resistant (MDR) ST infection, was also assessed at 4 and 24 hours post infection (pi) in the cecum and spleen, representing their mucosal and systemic immune responses, respectively.

Methods

A total of 375 samples from 130 diseased and apparently healthy broiler and layer chickens were randomly collected for Salmonella isolation, identification, and resistance profile evaluation, from farms and different clinical laboratories. The immune response of 1-day-old broiler chicks, Ross 308, against in-vivo ST infection was ascertained through the evaluation of heterophile phagocytosis and s expression of cytokines, immunoglobulin A and other immune-regulating genes in the cecum and spleen. Twenty-four, 1-day-old nonvaccinated broiler chicks were used and divided into two groups. The chicks in the infected group were orally inoculated with 0.5 ml of 2 × 108 colony forming units (CFU)/ml of MDR ST suspension, while those in the control group were taken nutrient broth.

Results

Seven out of 130 (5.38%) examined chickens were positive for Salmonella. All isolates (100%) were resistant to amoxicillin-clavulanic acid (AMC), cefazolin (CZ), cefoxitin (FOX), ciprofloxacin (CIP), nalidixic acid (NA), tetracycline (TE), fosfomycin (FOS), and colistin (CT) with multiple antimicrobial resistances (MARs) index range of 0.72-0.83, where none of them was resistant to meropenem (MEM). The results of immune response revealed that chicks infected with ST showed significantly different phagocytosis percentages and index values compared to controls. According to the real-time quantitative polymerase chain reaction (RT-qPCR) results, the transcription of IL-8, iNOS, IL-18, IgA, and IFN-γ for chicks infected by ST showed a significantly increased trend (p < 0.01) with increasing chicken age and was higher in the cecum than spleen compared to controls (p < 0.05) during 24 hours after infection.

Conclusion

The findings indicated a strong mucosal immune response in the chicks after the ST challenge, which reflects humoral and cellular responses. Our insight recommended the occurrence of a natural immune response stimulator at 1 day age to face the infection, and this can prevent the resistance transfer, with efficient control measures.

Evaluation of Virulence of Salmonella Infantis and Salmonella Enteritidis with In Vitro and In Vivo Models

Salmonella Infantis and Enteritidis serovars have been reported as important causes of salmonellosis in humans worldwide. However, the virulence of these two serovars has yet to be compared. To evaluate the virulence of Salmonella Infantis (n = 23) and Salmonella Enteritidis (n = 7), we used two models: the Caco2 cells model (in vitro) and the Galleria mellonella model (in vivo). Additionally, the virulence genes of all tested strains were contrasted with phenotypic outcomes. Results showed that adhesion means were 18.2% for Salmonella Enteritidis and 38.2% for Salmonella Infantis strains. Invasion means were 77.1% for Salmonella Enteritidis and 56.2% for Salmonella Infantis strains. Significant differences were found between serovars in adherence and invasion assays. Mortality rates (58% for Salmonella Enteritidis and 62.6% for Salmonella Infantis) were not significantly different between serotypes. The distribution of virulence genes showed that genes fae (fimbrial adherence determinants) and shdA (nonfimbrial adherence determinants) were only found in Salmonella Infantis strains. On the other hand, the rck gene (invasion) and Plasmid-encoded fimbriae genes (pef A, B, C, D) were present in Salmonella Enteritidis exclusively. In conclusion, this study shows that Salmonella Enteritidis has a higher virulence potential under experimental conditions than Salmonella Infantis. However, more studies are needed to determine the risk that Salmonella Infantis could represent compared with Salmonella Enteritidis. Moreover, other in vivo models should be considered to assess the virulence of these serovars.

Differential Salmonella Typhimurium intracellular replication and host cell responses in caecal and ileal organoids derived from chicken

Chicken infection with Salmonella Typhimurium is an important source of foodborne human diseases. Salmonella colonizes the avian intestinal tract and more particularly the caecum, without causing symptoms. This thus poses a challenge for the prevention of foodborne transmission. Until now, studies on the interaction of Salmonella with the avian gut intestine have been limited by the absence of in vitro intestinal culture models. Here, we established intestinal crypt-derived chicken organoids to better decipher the impact of Salmonella intracellular replication on avian intestinal epithelium. Using a 3D organoid model, we observed a significantly higher replication rate of the intracellular bacteria in caecal organoids than in ileal organoids. Our model thus recreates intracellular environment, allowing Salmonella replication of avian epithelium according to the intestinal segment. Moreover, an inhibition of the cellular proliferation was observed in infected ileal and caecal organoids compared to uninfected organoids. This appears with a higher effect in ileal organoids, as well as a higher cytokine and signaling molecule response in infected ileal organoids at 3 h post-infection (hpi) than in caecal organoids that could explain the lower replication rate of Salmonella observed later at 24 hpi. To conclude, this study demonstrates that the 3D organoid is a model allowing to decipher the intracellular impact of Salmonella on the intestinal epithelium cell response and illustrates the importance of the gut segment used to purify stem cells and derive organoids to specifically study epithelial cell -Salmonella interaction.

Influence of Live Attenuated Salmonella Vaccines on Cecal Microbiome Composition and Microbiota Abundances in Young Broiler Chickens

Salmonellosis is a global food safety challenge caused by Salmonella, a gram-negative bacterium of zoonotic importance. Poultry is considered a major reservoir for the pathogen, and humans are exposed through consumption of raw or undercooked products derived from them. Prophylaxis of Salmonella in poultry farms generally mainly involves biosecurity measures, flock testing and culling, use of antibiotics, and vaccination programs. For decades, the use of antibiotics has been a common practice to limit poultry contamination with important pathogenic bacteria such as Salmonella at the farm level. However, due to an increasing prevalence of resistance, non-therapeutic use of antibiotics in animal production has been banned in many parts of the world. This has prompted the search for non-antimicrobial alternatives. Live vaccines are among the developed and currently used methods for Salmonella control. However, their mechanism of action, particularly the effect they might have on commensal gut microbiota, is not well understood. In this study, three different commercial live attenuated Salmonella vaccines (AviPro^® Salmonella Vac T, AviPro^® Salmonella DUO, and AviPro^® Salmonella Vac E) were used to orally vaccinate broiler chickens, and cecal contents were collected for microbiomes analysis by 16S rRNA next generation sequencing. Quantitative real-time PCR (qPCR) was used to study the cecal immune-related genes expression in the treatment groups, while Salmonella-specific antibodies were analyzed from sera and cecal extracts by enzyme-linked immunosorbent assay (ELISA). We show that vaccination with live attenuated Salmonella vaccines had a significant influence on the variability of the broiler cecal microbiota (p = 0.016). Furthermore, the vaccines AviPro^® Salmonella Vac T and AviPro^® Salmonella DUO, but not AviPro^® Salmonella Vac E, had a significant effect (p = 0.024) on microbiota composition. This suggests that the live vaccine type used can differently alter the microbiota profiles, driving the gut colonization resistance and immune responses to pathogenic bacteria, and might impact the overall chicken health and productivity. Further investigation is, however, required to confirm this.

Effects of embryonic thermal manipulation on the immune response to post-hatch Escherichia coli challenge in broiler chicken

Background and Aim

Thermal manipulation (TM), exposure to mild heat shock during embryogenesis, which is a critical developmental period of broiler chickens, improves tissue stability, oxidative stress response, and immune response during heat stress. Thermal manipulation could be more cost-effective than other methods to boost the immune response. This study aimed to evaluate the impact of TM during embryogenesis, concomitant with an Escherichia coli challenge, on body weight (BW), body temperature (Tb), and splenic mRNA expression of cytokines (Interleukin [IL]-1β, IL-2, IL-6, IL-8, IL-12, IL-15, IL-16, IL-18, and interferon [IFN]-γ) in poultry.

Materials and Methods

A total of 740 fertile eggs were procured from a certified Ross broiler breeder. The eggs were divided into two incubation groups: the control and TM groups. The eggs in the control group were kept at 37.8°C air temperature and 56% relative humidity (RH) during incubation; eggs of the TM group were incubated under standard conditions, except for embryonic days 10-18, during which they were incubated at 39°C and 65% RH for 18 h daily. On the 7th day of incubation, eggs with dead embryos were excluded. After hatching was complete, each group was further subdivided into saline-treated or E. coli-challenged groups. The E. coli (serotype 078 with the dose of 1.5 × 105 colony-forming unit/mL) challenge was performed when the birds were 20 days old. Body weight and Tb measurements were taken on post-hatch days 20, 21, 23, and 25. Splenic mRNA expression of cytokines (IL-1β, IL-2, IL-6, IL-8, IL-12, IL-15, IL-16, IL-18, and IFN-γ) was analyzed by real-time quantitative polymerase chain reaction.

Results

Following the E. coli challenge, the TM-treated group's body performance parameters (BW and Tb) were significantly increased compared with the control group. Body weight was higher in the TM group than in the control group (p < 0.05); Tb was lower in the TM group than in the control group (p < 0.05). The mRNA levels of IL and IFN-γ were more stable and moderately induced in the TM group compared with the control group. Thermal manipulation altered the basal mRNA levels of ILs and IFN-γ and changed their expression dynamics after the E. coli challenge.

Conclusion

Thermal manipulation during embryogenesis could boost the immune system response to E. coli.

Identification of key transcription factors and their functional role involved in Salmonella typhimurium infection in chicken using integrated transcriptome analysis and bioinformatics approach

Salmonella enterica serovar typhimurium is the cause of significant morbidity and mortality worldwide that causes economic losses to poultry and is able to cause infection in humans. Indigenous chicken breeds are a potential source of animal protein and have the added advantage of being disease resistant. An indigenous chicken, Kashmir favorella and commercial broiler were selected for understanding the mechanism of disease resistance. Following infection in Kashmir favorella, three differentially expressed genes Nuclear Factor Kappa B (NF-κB1), Forkhead Box Protein O3 (FOXO3) and Paired box 5 (Pax5) were identified. FOXO3, a transcriptional activator, is the potential marker of host resistance in Salmonella infection. NF-κB1 is an inducible transcription factor which lays the foundation for studying gene network of the innate immune response of Salmonella infection in chicken. Pax5 is essential for differentiation of pre-B cells into mature B cell. The real time PCR analysis showed that in response to Salmonella Typhimurium infection a remarkable increase of NF-κB1 (P˂0.01)_, FOXO3 (P˂0.01) gene expression in liver and Pax5 (P˂0.01) gene expression in spleen of Kashmir favorella was observed. The protein-protein interaction (PPI) and protein-TF interaction network by STRINGDB analysis suggests that FOXO3 is a hub gene in the network and is closely related to Salmonella infection along with NF-κB1. All the three differentially expressed genes (NF-κB1, FOXO3 and PaX5) showed their influence on 12 interacting proteins and 16 TFs, where cyclic adenosine monophosphate Response Element Binding protein (CREBBP), erythroblast transformation-specific (ETSI), Tumour-protein 53(TP53I), IKKBK, lymphoid enhancer-binding factor-1 (LEF1), and interferon regulatory factor-4 (IRF4) play role in immune responses. This study shall pave the way for newer strategies for treatment and prevention of Salmonella infection and may help in increasing the innate disease resistance.

Effects of Lactobacillus fermentum Administration on Intestinal Morphometry and Antibody Serum Levels in Salmonella-Infantis-Challenged Chickens

There are no studies reporting the effects of Salmonella enterica subsp. enterica serovar Infantis (S. Infantis) on intestinal architecture and immunoglobulin serum levels in chickens. Here, we measured these parameters and hypothesized whether probiotic administration could modulate the observed outcomes. Two-hundred 1-day-old COBB 500 male chicks were allocated into four groups: (I) the control, (II) the group treated with L. fermentum, (III) the group exposed to S. Infantis, and (IV) the group inoculated with both bacteria. At 11 days post infection, blood was gathered from animals which were then euthanized, and samples from the small intestine were collected. Intestinal conditions, as well as IgA and IgM serum levels, were assessed. S. Infantis reduced villus-height-to-crypt-depth (VH:CD) ratios in duodenal, jejunal, and ileal sections compared to control conditions, although no differences were found regarding the number of goblet cells, muc-2 expression, and immunoglobulin concentration. L. fermentum improved intestinal measurements compared to the control; this effect was also evidenced in birds infected with S. Infantis. IgM serum levels augmented in response to the probiotic in infected animals. Certainly, the application of L. fermentum elicited positive outcomes in S. Infantis-challenged chickens and thus must be considered for developing novel treatments designed to reduce unwanted infections.

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.

Infection dynamics of Salmonella Infantis vary considerably between chicken lines

AbstractSalmonella (S.) Infantis is the most common serovar in broilers and broiler meat in the European Union. In the field, fast-growing broilers are reported to be more affected than slow-growing and layer birds. The present study investigated the infection dynamics and immunological response of four chicken lines in the course of a S. Infantis infection. Two commercial chicken lines, Ross 308 and Hubbard ISA-JA-757, and two experimentally chicken lines, specific pathogen free (SPF) layers and broilers, were infected at 2 days of age. Investigations focused on faecal shedding, bacterial colonisation, humoral and cellular immune response in the blood. Ross and SPF broilers were mainly attributed as high shedders followed by Hubbard. SPF layers showed the least shedding. This is in agreement with the caecal colonisation, SPF layers harboured significant less bacteria. Systemic spread of S. Infantis to liver and spleen was highest in Ross being statistically significant at 7 days of age compared to the other lines. Spread of infection to in-contact birds, was noticed 5 days post infection in every line. Antibody response occurred in every chicken line from day 21 of age onwards. In contrast to the other chicken lines, significant differences in T cell subsets and monocytes/macrophages were found between infected and negative Hubbard birds at 7 days of age. Uninfected SPF birds had significant higher immune cell counts (T cell subsets, B cells and monocytes /macrophages) compared to uninfected commercial birds, a fact important for future experimental settings. The results illustrate that the infection dynamics of S. Infantis is influenced by the chicken line resulting in a higher risk of transmission to humans from fast-growing broilers.

Immunization of Broiler Chickens With a Killed Chitosan Nanoparticle Salmonella Vaccine Decreases Salmonella Enterica Serovar Enteritidis Load

There is a critical need for an oral-killed Salmonella vaccine for broilers. Chitosan nanoparticle (CNP) vaccines can be used to deliver Salmonella antigens orally. We investigated the efficacy of a killed Salmonella CNP vaccine on broilers. CNP vaccine was synthesized using Salmonella enterica serovar Enteritidis (S. Enteritidis) outer membrane and flagella proteins. CNP was stable at acidic conditions by releasing 14% of proteins at pH 5.5. At 17 h post-incubation, the cumulative protein release for CNP was 75% at pH 7.4. Two hundred microliters of PBS with chicken red blood cells incubated with 20 μg/ml CNP released 0% hemoglobin. Three hundred chicks were allocated into 1) Control, 2) Challenge, 3) Vaccine + Challenge. At d1 of age, chicks were spray-vaccinated with PBS or 40 mg CNP. At d7 of age, chicks were orally-vaccinated with PBS or 20 μg CNP/bird. At d14 of age, birds were orally-challenged with PBS or 1 × 107 CFU/bird of S. Enteritidis. The CNP-vaccinated birds had higher antigen-specific IgY/IgA and lymphocyte-proliferation against flagellin (p &lt; 0.05). At 14 days post-infection, CNP-vaccinated birds reversed the loss in gut permeability by 13% (p &lt; 0.05). At 21 days post-infection, the CNP-vaccinated birds decreased S. Enteritidis in the ceca and spleen by 2 Log10 CFU/g, and in the small intestine by 0.6 Log10 CFU/g (p &lt; 0.05). We conclude that the CNP vaccine is a viable alternative to conventional Salmonella poultry vaccines.

Chicken-Specific Kinome Analysis of Early Host Immune Signaling Pathways in the Cecum of Newly Hatched Chickens Infected With Salmonella enterica Serovar Enteritidis

Poultry is a major source of human foodborne illness caused by broad host range Salmonella serovars (paratyphoid), and developing cost-effective, pre-harvest interventions to reduce these pathogens would be valuable to the industry and consumer. Host responses to infectious agents are often regulated through phosphorylation. However, proteomic mechanisms of Salmonella acute infection biology and host responses to the bacteria have been limited concentrating predominately on the genomic responses of the host to infection. Our recent development of chicken-specific peptide arrays for kinome analysis of host phosphorylation-based cellular signaling responses provided us with the opportunity to develop a more detailed understanding of the early (4-24 h post-infection) host-pathogen interactions during the initial colonization of the cecum by Salmonella. Using the chicken-specific kinomic immune peptide array, biological pathway analysis showed infection with S. Enteritidis increased signaling related to the innate immune response, relative to the non-infected control ceca. Notably, the acute innate immune signaling pathways were characterized by increased peptide phosphorylation (activation) of the Toll-like receptor and NOD-like receptor signaling pathways, the activation of the chemokine signaling pathway, and the activation of the apoptosis signaling pathways. In addition, Salmonella infection induced a dramatic alteration in the phosphorylation events of the JAK-STAT signaling pathway. Lastly, there is also significant activation of the T cell receptor signaling pathway demonstrating the initiation of the acquired immune response to Salmonella infection. Based on the individual phosphorylation events altered by the early Salmonella infection of the cecum, certain conclusions can be drawn: (1) Salmonella was recognized by both TLR and NOD receptors that initiated the innate immune response; (2) activation of the PPRs induced the production of chemokines CXCLi2 (IL-8) and cytokines IL-2, IL-6, IFN-α, and IFN-γ; (3) Salmonella infection targeted the JAK-STAT pathway as a means of evading the host response by targeting the dephosphorylation of JAK1 and TYK2 and STAT1,2,3,4, and 6; (4) apoptosis appears to be a host defense mechanism where the infection with Salmonella induced both the intrinsic and extrinsic apoptotic pathways; and (5) the T cell receptor signaling pathway activates the AP-1 and NF-κB transcription factor cascades, but not NFAT.

Pathogenesis-Related Gene Expression in Response to Trachyspermum ammi Supplementation Along With Probiotics in Chicken Salmonellosis and Insights in Drug Therapeutics

Salmonella enterica serovar typhimurium (S. typhimurium) is the leading cause of foodborne illness. Since Salmonella continues to have a detrimental effect on public health, there is an ongoing need to develop more advanced methods for combating Salmonellosis in foods before they reach consumers. In addition, the quest for alternative natural products has recently intensified due to increasingly stringent regulations regarding the use of antibiotics as growth promoters and consumer demand for antibiotic-free poultry products. This study evaluated the effect of Ajwain extract (AJE) on immune response and antioxidant status in broiler chicks challenged with Salmonella typhimurium. The chicks were infected with S. typhimurium and were divided into the different groups, except for the control group (CON). The challenged chicks received different treatments with 3 × 109 colony-forming unit (CFU) AciproTM-WS probiotic (PRO), 200 mg/kg Ajwain extract (AJE), 200 mg/100 kg of enrofloxacin (ENR), and a combination of 3 × 109 CFU AciproTM-WS probiotic and 200 mg/kg Ajwain extract (COM). Five days posttreatment, the tissue samples (liver and spleen) were analyzed. The results showed that basal diet supplemented with Ajwain extract (AJE) and a combination of probiotic and Ajwain extract (COM) significantly (P &lt; 0.0.5) reduced the cytokine expression in broiler chicks challenged with S. typhimurium. Our findings suggest that AJE can clear the bacterial infection, improve antioxidant status, and suppress the inflammation response. Additionally, AJE supplementation significantly mitigated the S. typhimurium-induced increase in the interleukin-6 (IL-6) (liver and spleen), interleukin-8 (IL-8) (liver and spleen), interleukin-17A (IL-17A) (liver and spleen), and inducible nitric oxide (iNOS) (spleen and liver) levels (P &lt; 0.05). We conclude that Ajwain is an efficient feed additive with antioxidant and anti-inflammatory properties. The interaction networks developed in this study provide a novel lead that could be targeted for anti-inflammatory and antioxidant properties.

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

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

Infection dynamics of Salmonella Infantis strains displaying different genetic backgrounds - with or without pESI-like plasmid - vary considerably

Food-borne infections with Salmonella are among the most common causes of human diseases worldwide, and infections with the serovar Infantis are becoming increasingly important. So far, diverse phenotypes and genotypes of S. Infantis have been reported. Therefore, the present study aimed to investigate the infection dynamics of two different S. Infantis strains in broilers. For this purpose, 15 birds were infected on day 2 of life with 108 CFU/ml of a pESI+ or a pESI- S. Infantis strain, respectively. Ten uninfected birds served as in-contact birds to monitor transmission. In both groups, an increase of infection was observed from 7 days of age onwards, reaching its peak at 28 days. However, the pESI+ strain proved significantly more virulent being re-isolated from most cloacal swabs and organs by direct plating. In contrast, the pESI- strain could be re-isolated from cloacal swabs and caeca only when enrichment was applied. Although the excretion of this strain was limited, the transmission level to in-contact birds was similar to the pESI+ strain. Differences in infection dynamics were also reflected in the antibody response: whereas the pESI+ strain provoked a significant increase in antibodies, antibody levels following infection with the pESI- strain remained in the range of negative control birds. The actual findings provide for the first time evidence of S. Infantis strain-specific infectivity in broilers and confirm previous observations in the field regarding differences in persistence on farms and resistance against disinfectants.

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.

Revisiting Persistent Salmonella Infection and the Carrier State: What Do We Know?

One characteristic of the few Salmonella enterica serovars that produce typhoid-like infections is that disease-free persistent infection can occur for months or years in a small number of individuals post-convalescence. The bacteria continue to be shed intermittently which is a key component of the epidemiology of these infections. Persistent chronic infection occurs despite high levels of circulating specific IgG. We have reviewed the information on the basis for persistence in S. Typhi, S. Dublin, S. Gallinarum, S. Pullorum, S. Abortusovis and also S. Typhimurium in mice as a model of persistence. Persistence appears to occur in macrophages in the spleen and liver with shedding either from the gall bladder and gut or the reproductive tract. The involvement of host genetic background in defining persistence is clear from studies with the mouse but less so with human and poultry infections. There is increasing evidence that the organisms (i) modulate the host response away from the typical Th1-type response normally associated with immune clearance of an acute infection to Th2-type or an anti-inflammatory response, and that (ii) the bacteria modulate transformation of macrophage from M1 to M2 type. The bacterial factors involved in this are not yet fully understood. There are early indications that it might be possible to remodulate the response back towards a Th1 response by using cytokine therapy.

Interaction of Salmonella Gallinarum and Salmonella Enteritidis with peripheral leucocytes of hens with different laying performance

Salmonella enterica ssp. enterica serovars Enteritidis (SE) and Gallinarum (SG) cause different diseases in chickens. However, both are able to reach the blood stream where heterophils and monocytes are potentially able to phagocytose and kill the pathogens. Using an ex vivo chicken whole blood infection model, we compared the complex interactions of the differentially host-adapted SE and SG with immune cells in blood samples of two White Leghorn chicken lines showing different laying performance (WLA: high producer; R11: low producer). In order to examine the dynamic interaction between peripheral blood leucocytes and the Salmonella serovars, we performed flow cytometric analyses and survival assays measuring (i) leucocyte numbers, (ii) pathogen association with immune cells, (iii) Salmonella viability and (iv) immune gene transcription in infected whole blood over a four-hour co-culture period. Inoculation of blood from the two chicken lines with Salmonella led primarily to an interaction of the bacteria with monocytes, followed by heterophils and thrombocytes. We found higher proportions of monocytes associated with SE than with SG. In blood samples of high producing chickens, a decrease in the numbers of both heterophils and Salmonella was observed. The Salmonella challenge induced transcription of interleukin-8 (IL-8) which was more pronounced in SG- than SE-inoculated blood of R11. In conclusion, the stronger interaction of monocytes with SE than SG and the better survivability of Salmonella in blood of low-producer chickens shows that the host-pathogen interaction and the strength of the immune defence depend on both the Salmonella serovar and the chicken line.

A Novel Approach against Salmonella: A Review of Polymeric Nanoparticle Vaccines for Broilers and Layers

This work discusses the present-day limitations of current commercial Salmonella vaccines for broilers and layers and explores a novel approach towards poultry vaccination using biodegradable nanoparticle vaccines against Salmonella. With the increasing global population and poultry production and consumption, Salmonella is a potential health risk for humans. The oral administration of killed or inactivated vaccines would provide a better alternative to the currently commercially available Salmonella vaccines for poultry. However, there are currently no commercial oral killed-vaccines against Salmonella for use in broilers or layers. There is a need for novel and effective interventions in the poultry industry. Polymeric nanoparticles could give way to an effective mass-administered mucosal vaccination method for Salmonella. The scope of this work is limited to polymeric nanoparticles against Salmonella for use in broilers and layers. This review is based on the information available at the time of the investigation.

Intra- and inter-breed variation in immune response to acute and sub-chronic Salmonella infection and commercial immune-stimulant in two-layer breeds

Salmonella is one of the most hazardous diseases in poultry farms. Markedly, the application of active immunostimulants is illustrated as potential protective agents against infection in poultry farms. Thus, this work aimed to explore inter- and intra-breed variation in response to acute and subchronic Salmonella enteritidis infection in two-layer breeds (one commercial [Hy-line strain] and another native [Fayoumi breed]). Besides exploring the possible protective effect of a commercial immune modulator (STIMULAN) on the two breeds during the acute infection. The ELISA antibody titer in sub-chronic infections and the expression analysis of some selected genes (IL-1β, LITAF, TGF-β, HSP90 and HSP70) are used as the clinical signs for acute infections to assess the possible protective role of a commercial immunomodulator (STIMULAN). Five groups were used during the acute experiment: G1-control; G2a-susceptible; G2b-resistant birds, G3-which received STIMULAN and G4-which received the infection + STIMULAN. The groups with sub-chronic infections include G1 (control), G2 (high antibody titer) and G3 (low antibody titer). The gene expressions among the susceptible birds during acute infection of both breeds are nearly similar. They only differ in the expression of HSP90 in the Fayoumi breed. However, the resistant birds vary in their gene expression profile. The effect of STIMULAN as a feed additive in non-infected birds was an up-regulation of LITAF, TGF-β, HSP90 in Fayoumi. Moreover, a powerful stimulatory role was observed when both breeds were infected. Both breeds were asymptomatic during the sub-chronic infection. Although, the increased expression of inflammatory-related genes in the Hy-line was considered as an indication of infection persistence. Fayoumi is capable of immune clearance for this infection. Thus, the Fayoumi breed is more resistant to acute Salmonella infection. HSP90 plays a vital role in its resistance. We recommend the use of STIMULAN as an immunomodulator during Salmonella infection.

Characteristics of systemic infection and host responses in chickens experimentally infected with Salmonella enterica serovar Gallinarum biovar Gallinarum

Salmonella enterica serovar Gallinarum biovar Gallinarum (S. Gallinarum) is a host-specific pathogen causing systemic infection in poultry, which leads to significant economic losses due to high mortality. However, little is known about the dynamic process of systemic infection and pathogenic characteristics of S. Gallinarum in chickens. In the present study, we developed an oral infection model that reproduces the pathology of S. Gallinarum and clarified the host immune response of the infected chickens. Chickens at 20 days of age orally inoculated at a dose of 10⁸ colony forming unit (CFU) showed typical clinical signs of fowl typhoid and died between 6 and 10 days post infection. The inoculated S. Gallinarum rapidly disseminated to multple organs and the bacterial counts increased in the liver and spleen at 3 days post infection. Pathological changes associated wirh inflammation in the liver and spleen became apparent at 4 days post infection, and increased expression of interferon (IFN)-γ and interleuikin (IL)-12 in the liver and spleen did not observed until 3 days post infection. These results indicate that S. Gallinarum rapidly spread to entire body through intestine, and the low-level of inflammatory responses in the liver during the early stage of infection may contribute to rapid, systemic dissemination of the bacteria. Our infection model and findings will contribute to the better understanding of the pathogenic mechanism of S. Gallinarum, and provide new insights into the prevention and control of fowl typhoid.

Modernization of Control of Pathogenic Micro-Organisms in the Food-Chain Requires a Durable Role for Immunoaffinity-Based Detection Methodology-A Review

Food microbiology is deluged by a vastly growing plethora of analytical methods. This review endeavors to color the context into which methodology has to fit and underlines the importance of sampling and sample treatment. The context is that the highest risk of food contamination is through the animal and human fecal route with a majority of foodborne infections originating from sources in mass and domestic kitchens at the end of the food-chain. Containment requires easy-to-use, failsafe, single-use tests giving an overall risk score in situ. Conversely, progressive food-safety systems are relying increasingly on early assessment of batches and groups involving risk-based sampling, monitoring environment and herd/flock health status, and (historic) food-chain information. Accordingly, responsible field laboratories prefer specificity, multi-analyte, and high-throughput procedures. Under certain etiological and epidemiological circumstances, indirect antigen immunoaffinity assays outperform the diagnostic sensitivity and diagnostic specificity of e.g., nucleic acid sequence-based assays. The current bulk of testing involves therefore ante- and post-mortem probing of humoral response to several pathogens. In this review, the inclusion of immunoglobulins against additional invasive micro-organisms indicating the level of hygiene and ergo public health risks in tests is advocated. Immunomagnetic separation, immunochromatography, immunosensor, microsphere array, lab-on-a-chip/disc platforms increasingly in combination with nanotechnologies, are discussed. The heuristic development of portable and ambulant microfluidic devices is intriguing and promising. Tant pis, many new platforms seem unattainable as the industry standard. Comparability of results with those of reference methods hinders the implementation of new technologies. Whatever the scientific and technological excellence and incentives, the decision-maker determines this implementation after weighing mainly costs and business risks.

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.

Transcriptional response of blood leukocytes from turkeys challenged with Salmonella enterica serovar Typhimurium UK1

Non-typhoidal Salmonella is one of the most common causes of bacterial foodborne disease and consumption of contaminated poultry products, including turkey, is one source of exposure. Minimizing Salmonella colonization of commercial turkeys could decrease the incidence of Salmonella-associated human foodborne illness. Understanding host responses to these bacteria is critical in developing strategies to minimize colonization and reduce food safety risk. In this study, we evaluated bacterial load and blood leukocyte transcriptomic responses of 3-week-old turkeys challenged with the Salmonella enterica serovar Typhimurium (S. Typhimurium) UK1 strain. Turkeys (n = 8/dose) were inoculated by oral gavage with 10⁸ or 10¹⁰ colony forming units (CFU) of S. Typhimurium UK1, and fecal shedding and tissue colonization were measured across multiple days post-inoculation (dpi). Fecal shedding was 1-2 log₁₀ higher in the 10¹⁰ CFU group than the 10⁸ CFU group, but both doses effectively colonized the crop, spleen, ileum, cecum, colon, bursa of Fabricius and cloaca without causing any detectable clinical signs in either group of birds. Blood leukocytes were isolated from a subset of the birds (n = 3-4/dpi) both pre-inoculation (0 dpi) and 2 dpi with 10¹⁰ CFU and their transcriptomic responses assayed by RNA-sequencing (RNA-seq). At 2 dpi, 647 genes had significant differential expression (DE), including large increases in expression of immune genes such as CCAH221, IL4I1, LYZ, IL13RA2, IL22RA2, and ACOD1. IL1β was predicted as a major regulator of DE in the leukocytes, which was predicted to activate cell migration, phagocytosis and proliferation, and to impact the STAT3 and toll-like receptor pathways. These analyses revealed genes and pathways by which turkey blood leukocytes responded to the pathogen and can provide potential targets for developing intervention strategies or diagnostic assays to mitigate S. Typhimurium colonization in turkeys.

Challenges in Vaccinating Layer Hens against Salmonella Typhimurium

Salmonella Typhimurium is among the most common causes of bacterial foodborne gastrointestinal disease in humans. Food items containing raw or undercooked eggs are frequently identified during traceback investigation as the source of the bacteria. Layer hens can become persistently infected with Salmonella Typhimurium and intermittently shed the bacteria over the course of their productive lifetime. Eggs laid in a contaminated environment are at risk of potential exposure to bacteria. Thus, mitigating the bacterial load on farms aids in the protection of the food supply chain. Layer hen producers use a multifaceted approach for reducing Salmonella on farms, including the all-in-all-out management strategy, strict biosecurity, sanitization, and vaccination. The use of live attenuated Salmonella vaccines is favored because they elicit a broader host immune response than killed or inactivated vaccines that have been demonstrated to provide cross-protection against multiple serovars. Depending on the vaccine, two to three doses of Salmonella Typhimurium vaccines are generally administered to layer hens within the first few weeks. The productive life of a layer hen, however, can exceed 70 weeks and it is unclear whether current vaccination regimens are effective for that extended period. The objective of this review is to highlight layer hen specific challenges that may affect vaccine efficacy.

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

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

Live Bacterial Prophylactics in Modern Poultry

Commercial poultry farms frequently use live bacterial prophylactics like vaccines and probiotics to prevent bacterial infections. Due to the emergence of antibiotic-resistant bacteria in poultry animals, a closer examination into the health benefits and limitations of commercial, live prophylactics as an alternative to antibiotics is urgently needed. In this review, we summarize the peer-reviewed literature of several commercial live bacterial vaccines and probiotics. Per our estimation, there is a paucity of peer-reviewed published research regarding these products, making repeatability, product-comparison, and understanding biological mechanisms difficult. Furthermore, we briefly-outline significant issues such as probiotic-label accuracy, lack of commercially available live bacterial vaccines for major poultry-related bacteria such as Campylobacter and Clostridium perfringens, as well research gaps (i.e., probiotic-mediated vaccine adjuvancy, gut-brain-microbiota axis). Increased emphasis on these areas would open several avenues for research, ranging from improving protection against bacterial pathogens to using these prophylactics to modulate animal behavior.

Yeast cell wall product enhanced intestinal IgA response and changed cecum microflora species after oral vaccination in chickens

The study was designed to explore the effect of a commercial yeast cell wall product (YP) on chicken intestinal IgA response and cecum microbiome after oral vaccination. Chickens were fed with YP during the experiments and orally immunized with live Newcastle disease virus (NDV) vaccine at 2 wk of age. Then, the animals were sacrificed, and samples were collected to measure the indicators of hemagglutination inhibition (HI), IgA response, IgA + cells, and cecum microbiome populations. The results showed that supplement of YP significantly enhanced serum NDV HI titer, intestinal NDV-specific secretory IgA, and intestinal IgA + cells. The sequencing results revealed that obviously increased relative abundance of Ruminococcaceae and decreased population of Bacteroidaceae in cecum were found in YP group. In summary, YP supplementation in diet enhanced intestinal IgA response to NDV vaccination by oral route and modulated the cecum microbiota to the advantage of the host in chickens.

Transcriptome profiling analysis of caeca in chicks challenged with Salmonella Typhimurium reveals differential expression of genes involved in host mucosal immune response

Temporal regulation of global gene expression in the caeca of chickens infected with Salmonella Typhimurium has not been investigated previously. In this study, we performed the transcriptome analysis of the caeca of Salmonella Typhimurium challenged chicks to understand the regulation of the mucosal immune system in a temporal manner. The Salmonella infection resulted in the activation of the caecal immune system by the upregulation of the differentially expressed genes (DEGs; false discovery rate (FDR) < 0.05; log₂ fold change > 1) involved in biological pathways such as Toll-like receptor signaling pathway, Salmonella infection, cytokine-cytokine receptor interaction, phagosome, apoptosis and intestinal immune network for IgA production. The activation of biological pathways such as RIG-I-like receptor signaling pathway, ErbB signaling pathway and cellular senescence showed a time-dependent response of the host immune system. A 49% increase in the DEGs on day 7 compared with day 3 post-infection (p.i.) suggested a time-dependent role of multiple genes such as AvBD1, AvBD2, AvBD7, IL2, IL10, IL21, SIVA1, CD5, CD14 and GPR142 in the regulation of the immune system. Nested network analysis of the individual biological pathways showed that IL6 played a significant role in the immune system regulation by activating the pathways, including Toll-like receptor signaling pathway, Salmonella infection, intestinal immune network for IgA production and C-type lectin receptor signaling pathway. The downregulated DEGs (FDR < 0.05; log₂ fold change < -1) showed that Salmonella challenge affected the functions of pathways, such as tryptophan metabolism, retinol metabolism, folate biosynthesis and pentose and glucoronate interconversions, suggesting the disruption of cellular mechanisms involved in nutrient synthesis, absorption and metabolism. Overall, the immune response was temporally regulated through the activation of Toll-like signaling receptor pathway, cytokine-cytokine interactions and Salmonella infection, where IL6 played a significant role in the modulation of caecal immune system against Salmonella Typhimurium. KEY POINTS: • The immune response to Salmonella Typhimurium challenge was temporally regulated in the caeca of chickens. • Many newly identified genes have been shown to be involved in the activation of the immune system. • Toll-like receptors and interleukins played a key role in immune system regulation.

The Contribution of Eimeria Coinfection and Intestinal Inflammation to Cecal Colonization and Systemic Spread of Salmonella Typhimurium Deficient in Tetrathionate Reductase or Type III Secretion Systems Salmonella Pathogenicity Island 1 or 2

Intestinal inflammation may provide a growth advantage for Salmonella and enhance its systemic spread in chickens. Salmonella triggers intestinal inflammation in the host by using type III secretion systems (T3SS) and produces the inflammatory end product tetrathionate. In mice, tetrathionate respiration confers a growth advantage for Salmonella Typhimurium over the competitive microbiome in the inflamed intestine. Coccidia also promote intestinal inflammation and enhance Salmonella intestinal growth and systemic spread in chickens. The objective of this study was to evaluate the contribution of inflammation, induced by Eimeria spp. or Salmonella Typhimurium, to Salmonella colonization and dissemination in chickens. In addition, the fitness costs associated with defects in tetrathionate reductase and T3SS associated with Salmonella Pathogenicity Island 1 or 2 (SPI-1 or SPI-2) were evaluated in in vivo competition experiments with wild-type Salmonella strain, with or without Eimeria coinfection. One-day-old specific-pathogen-free chickens were orally inoculated with a sham inoculum or with 4 × 10² Eimeria oocysts cocktail of Eimeria tenella, Eimeria acervulina, Eimeria maxima, and Eimeria mitis. At 6 days of age, birds were orally administered a 1:1 ratio of Salmonella Typhimurium wild-type and mutant deficient in tetrathionate reductase, SPI-1, or SPI-2 (10⁸ colony forming units/bird). Ceca, livers, and drumsticks were collected at 3, 7, 14, and 42 days after Salmonella infection, for bacteriology. Intestinal inflammation was scored by histology. Significantly higher intestinal inflammation was observed in challenge groups compared with the control. However, there were no significant differences in intestinal inflammation scores between groups coinfected with both Eimeria spp. and Salmonella Typhimurium and birds infected with Salmonella alone, and Eimeria coinfection did not increase Salmonella prevalence or abundance. Contrary to mouse studies, tetrathionate reductase did not enhance Salmonella Typhimurium cecal colonization or systemic spread in chickens. SPI-1 and SPI-2 played a significant role in Salmonella dissemination and cecal colonization in chickens, respectively.

Impact of Dietary Manganese on Intestinal Barrier and Inflammatory Response in Broilers Challenged with Salmonella Typhimurium

Growing concern for public health and food safety has prompted a special interest in developing nutritional strategies for removing waterborne and foodborne pathogens, including Salmonella. Strong links between manganese (Mn) and intestinal barrier or immune function hint that dietary Mn supplementation is likely to be a promising approach to limit the loads of pathogens in broilers. Here, we provide evidence that Salmonella Typhimurium (S. Typhimurium, 4 × 10⁸ CFUs) challenge-induced intestinal injury along with systemic Mn redistribution in broilers. Further examining of the effect of dietary Mn treatments (a basal diet plus additional 0, 40, or 100 mg Mn/kg for corresponding to Mn-deficient, control, or Mn-surfeit diet, respectively) on intestinal barrier and inflammation status of broilers infected with S. Typhimurium revealed that birds fed the control and Mn-surfeit diets exhibited improved intestinal tight junctions and microbiota composition. Even without Salmonella infection, dietary Mn deficiency alone increased intestinal permeability by impairing intestinal tight junctions. In addition, when fed the control and Mn-surfeit diets, birds showed decreased Salmonella burdens in cecal content and spleen, with a concomitant increase in inflammatory cytokine levels in spleen. Furthermore, the dietary Mn-supplementation-mediated induction of cytokine production was probably associated with the nuclear factor kappa-B (NF-κB)/hydrogen peroxide (H₂O₂) pathway, as judged by the enhanced manganese superoxide dismutase activity and the increased H₂O₂ level in mitochondria, together with the increased mRNA level of NF-κB in spleen. Ingenuity-pathway analysis indicated that acute-phase response pathways, T helper type 1 pathway, and dendritic cell maturation were significantly activated by the dietary Mn supplementation. Our data suggest that dietary Mn supplementation could enhance intestinal barrier and splenic inflammatory response to fight against Salmonella infection in broilers.

Interleukin 4 inducible 1 gene (IL4I1) is induced in chicken phagocytes by Salmonella Enteritidis infection

In attempt to identify genes that are induced in chickens by Salmonella Enteritidis we identified a new highly inducible gene, interleukin 4 induced 1 gene (IL4I1). IL4I1 reached its peak expression (458× induction) in the cecum of newly hatched chickens 4 days post-infection and remained upregulated for an additional 10 days. IL4I1 was expressed and induced in macrophages and granulocytes, both at the mRNA and protein level. IL4I1 was expressed and induced also in CD4 and γδ T-lymphocytes though at a 50-fold lower level than in phagocytes. Expression of IL4I1 was not detected in CD8 T lymphocytes or B lymphocytes. Mutation of IL4I1 in chicken HD11 macrophages did not affect their bactericidal capacity against S. Enteritidis but negatively affected their oxidative burst after PMA stimulation. We therefore propose that IL4I1 is not directly involved in bactericidal activity of phagocytes and, instead, it is likely involved in the control of inflammatory response and signaling to T and B lymphocytes.

Dynamic Interplay of Host and Pathogens in an Avian Whole-Blood Model

Microbial survival in blood is an essential step toward the development of disseminated diseases and blood stream infections. For poultry, however, little is known about the interactions of host cells and pathogens in blood. We established an ex vivo chicken whole-blood infection assay as a tool to analyze interactions between host cells and three model pathogens, Escherichia coli, Staphylococcus aureus, and Candida albicans. Following a systems biology approach, we complemented the experimental measurements with functional and quantitative immune characteristics by virtual infection modeling. All three pathogens were killed in whole blood, but each to a different extent and with different kinetics. Monocytes, and to a lesser extent heterophils, associated with pathogens. Both association with host cells and transcriptional activation of genes encoding immune-associated functions differed depending on both the pathogen and the genetic background of the chickens. Our results provide first insights into quantitative interactions of three model pathogens with different immune cell populations in avian blood, demonstrating a broad spectrum of different characteristics during the immune response that depends on the pathogen and the chicken line.

Interaction of Salmonella enterica with Bovine Epithelial Cells Demonstrates Serovar-Specific Association and Invasion Patterns

Dairy cows are known reservoirs of Salmonella enterica and human salmonellosis has been attributed to the consumption of contaminated dairy and beef products as well as poultry meat and eggs. Although many S. enterica serovars are known to colonize the gastrointestinal tract of cattle, the interactions between dairy commensal (or persistent) and transient Salmonella serovars with bovine epithelial cells are not well understood. Association-invasion assays were used to characterize the interactions of 26 S. enterica strains from bovine origins, comprising serovars Anatum, Cerro, Dublin, Give, Kentucky, Mbandaka, Meleagridis, Montevideo, Muenster, Newport, Oranienburg, Senftenberg, and Typhimurium, with cultured bovine epithelial cells. There were significant differences in the association with and invasion of bovine epithelial cells within and across Salmonella serovars (Tukey's Honestly Significant Difference test, p < 0.05). Salmonella enterica serovar Dublin strains were the most invasive, whereas Kentucky, Mbandaka, Cerro, and Give strains were the least invasive (p < 0.05). Significant differences in motility on semisolid medium were also observed between strains from different serovars. Findings from this study demonstrate an underappreciated level of phenotypic diversity among Salmonella strains within and across serovars and serve as a baseline for future studies that may identify the molecular mechanisms of asymptomatic Salmonella carriage and bovine salmonellosis.

Dynamics and Outcome of Macrophage Interaction Between Salmonella Gallinarum, Salmonella Typhimurium, and Salmonella Dublin and Macrophages From Chicken and Cattle

Salmonella Gallinarum only infects avian species, where it causes a severe systemic infection in birds of all ages. It is generally accepted that interaction with phagocytic cells plays an important role in the development of systemic, host-specific Salmonella infections. The current study detailed the interaction of S. Gallinarum with macrophages derived from chicken (HD11) and cattle (Bomac) compared to interaction of the broad host range serovar, Salmonella Typhimurium and the cattle adapted serovar Salmonella Dublin. Results showed a weaker invading ability of S. Gallinarum in both kinds of macrophages, regardless whether the bacteria were opsonized or not before infections. However, opsonization of S. Gallinarum by chicken serum increased its intracellular survival rate in chicken macrophages. No significant induction of nitrogen oxide was observed in the infected HD11 cells within the first 6 h, and levels of reactive oxygen species (ROS) were similar among the three serovars. S. Gallinarum infection was associated with low cell deaths in both chicken and cattle macrophages, whereas S. Dublin only induced a comparable high level of cell death in chicken macrophages, but not in macrophages of its preferred host species (Bomac) compared to host generalist S. Typhimurium. S. Gallinarum-infected HD11 macrophages exhibited low induction of pro-inflammation genes [interleukin (IL)1β, CXCLi1, and CXCLi2] compared to the two other serovars, and contrary to the other serovars, it did not induce significant downregulation of Toll-like receptor (TLR)2, TLR4, and TLR5. In in vivo infection of 1-week-old chicken, a significant upregulation of the TLR4 and TLR5 genes in the spleen was observed in S. Gallinarum-infected chickens, but not in S. Typhimurium-infected chicken at 5 days post-infections. Taken together, results show that S. Gallinarum infection of macrophages was characterized by low uptake and low cytotoxicity, possibly allowing long-term persistence in the intracellular environment, and it caused a low induction of pro-inflammatory responses.

Serum amyloid A (SAA) mRNA expression in chicken and quails in response to bacterial stress

Monitoring of acute phase proteins such as serum amyloid A at gene expression level may provide quick information about immune status of the host and its susceptibility towards common infections. Present study was carried out to evaluate and compare the mRNA expression of SAA gene in Rhode Island Red chicken (RIR) and Japanese quails using real time PCR analysis in response to inactivated Salmonella gallinarum culture. The results showed that expression of SAA gene was approximately 17-33 folds higher in case of birds administered with bacterial culture when compared to un-inoculated controls and expression was higher and quicker in case of quails than RIR chicken. The SAA genes from chicken and quail were cloned and upon sequence analysis it was observed that deduced amino acid sequence of SAA from chicken and quails were having approximately seven percent variation which might have significance in function of this protein in these species.

Development of innate immunity in chicken embryos and newly hatched chicks: a disease control perspective

Newly hatched chickens are confronted by a wide array of pathogenic microbes because their adaptive immune defences have limited capabilities to control these pathogens. In such circumstances, and within this age group, innate responses provide a degree of protection. Moreover, as the adaptive immune system is relatively naïve to foreign antigens, synergy with innate defences is critical. This review presents knowledge on the ontogeny of innate immunity in chickens pre-hatch and early post-hatch and provides insights into possible interventions to modulate innate responses early in the life of the bird. As in other vertebrate species, the chicken innate immune system which include cellular mediators, cytokine and chemokine repertoires and molecules involved in antigen detection, develop early in life. Comparison of innate immune systems in newly hatched chickens and mature birds has revealed differences in magnitude and quality, but responses in younger chickens can be boosted using innate immune system modulators. Functional expression of pattern recognition receptors and several defence molecules by innate immune system cells of embryos and newly hatched chicks suggests that innate responses can be modulated at this stage of development to combat pathogens. Improved understanding of innate immune system ontogeny and functionality in chickens is critical for the implementation of sound and safe interventions to provide long-term protection against pathogens. Next-generation tools for studying genetic and epigenetic regulation of genes, functional metagenomics and gene knockouts can be used in the future to explore and dissect the contributions of signalling pathways of innate immunity and to devise more efficacious disease control strategies.

The Effect of Prebiotic Administration in the Diet at Unusual Times on Fecal Shedding of Salmonella enteritidis and Meat Characteristics of Broilers

Background: One of the most important foodborne pathogen which causes enteritis is Salmonella enteritidis (SE). Human cases are mostly associated with the consumption of eggs and poultry meat. Objective: An experiment has been carried out to evaluate the impacts of a yeast product as liquid prebiotic on bacterial shedding, performance indices, and some breast meat characteristics of broiler chickens challenged with SE. Materials and Methods: A total of 90 one-day-old male broiler chicks (Ross 308) were randomly assigned to three different groups with three replicates for each treatment. The treatments were as follows: (1) CONT: birds were not challenged, (2) SE: birds were challenged with SE and fed with a control diet without prebiotic, and (3) SE+PREB: birds were challenged with SE and fed with liquid prebiotic. The challenge with SE was performed on birds in groups 2 and 3 at 28 days of age. Performance parameters and Salmonella shedding were determined on days 7 and 14 post infection. Twelve birds per treatment were sampled at the end of the trial for evaluating characteristics of breast meat. Results: The challenged birds which received prebiotic showed significantly higher body weight gain, lower feed intake, and lower SE shedding than SE group (P<0.05). No significant differences were seen in meat characteristics. Conclusion: Prebiotics can have beneficial effects even if they are used in the diet at an unusual time. The supplementation of yeast product can improve some performance parameters and reduce bacterial shedding in SE challenged chicken.