Effects of Salmonella Enteritidis infection on TLRs gene expression and microbial diversity in cecum of laying hens

Differential expression of Toll-like receptors and associated cytokines in the bursa of Eimeria tenella infected chickens

Chicken coccidiosis, caused by Eimeria spp., is an economically important disease of commercial poultry. Innate immunity ensures an immediate response to invading parasites, and Toll-like receptors (TLRs) are major components of the innate immune system. However, few systematic studies have been reported on the roles of TLRs in chickens infected with Eimeria. In the present study, 14-day-old chickens were infected orally with 50,000 E. tenella oocysts and the bursa of Fabricius was dissected at different time points. Expression profiles of 10 chicken TLRs (chTLRs) and associated cytokines were determined by quantitative real-time PCR. The results showed that chTLR1a and chTLR2a peaked significantly at 3 h post-infection (p < 0.05), while other chTLRs displayed different expression profiles; chTLR1b, chTLR2b, chTLR5, and chTLR15 peaked at 48 h post-infection, while chTLR4, chTLR7, and chTLR21 peaked at 144 h post-infection. ChTLR3 expression was the highest among chTLRs, peaking at 96 h post-infection (p < 0.05). For cytokines, interleukin (IL)-6, IL-12, IL-17, and interferon-γ peaked at 12 h post-infection, while IL-4 peaked at 24 h post-infection. The results provide a valuable overview of the expression profiles of innate immune molecules during E. tenella infection in chicken bursa, and indicate that innate immune responses may mediate resistance to chicken coccidiosis.

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.

Dietary bile acids supplementation protects against Salmonella Typhimurium infection via improving intestinal mucosal barrier and gut microbiota composition in broilers

BACKGROUND

Salmonella Typhimurium (S. Typhimurium) is a common pathogenic microorganism and poses a threat to the efficiency of poultry farms. As signaling molecules regulating the interaction between the host and gut microbiota, bile acids (BAs) play a protective role in maintaining gut homeostasis. However, the antibacterial effect of BAs on Salmonella infection in broilers has remained unexplored. Therefore, the aim of this study was to investigate the potential role of feeding BAs in protecting against S. Typhimurium infection in broilers.

METHODS

A total of 144 1-day-old Arbor Acres male broilers were randomly assigned to 4 groups, including non-challenged birds fed a basal diet (CON), S. Typhimurium-challenged birds (ST), S. Typhimurium-challenged birds treated with 0.15 g/kg antibiotic after infection (ST-ANT), and S. Typhimurium-challenged birds fed a basal diet supplemented with 350 mg/kg of BAs (ST-BA).

RESULTS

BAs supplementation ameliorated weight loss induced by S. Typhimurium infection and reduced the colonization of Salmonella in the liver and small intestine in broilers (P < 0.05). Compared to the ST group, broilers in ST-BA group had a higher ileal mucosal thickness and villus height, and BAs also ameliorated the increase of diamine oxidase (DAO) level in serum (P < 0.05). It was observed that the mucus layer thickness and the number of villous and cryptic goblet cells (GCs) were increased in the ST-BA group, consistent with the upregulation of MUC2 gene expression in the ileal mucosa (P < 0.05). Moreover, the mRNA expressions of Toll-like receptor 5 (TLR5), Toll-like receptor 4 (TLR4), and interleukin 1 beta (IL1b) were downregulated in the ileum by BAs treatment (P < 0.05). 16S rDNA sequencing analysis revealed that, compared to ST group, BAs ameliorated the decreases in Bacteroidota, Bacteroidaceae and Bacteroides abundances, which were negatively correlated with serum DAO activity, and the increases in Campylobacterota, Campylobacteraceae and Campylobacter abundances, which were negatively correlated with body weight but positively correlated with serum D-lactic acid (D-LA) levels (P < 0.05).

CONCLUSIONS

Dietary BAs supplementation strengthens the intestinal mucosal barrier and reverses dysbiosis of gut microbiota, which eventually relieves the damage to the intestinal barrier and weight loss induced by S. Typhimurium infection in broilers.

Tackling salmonellosis: A comprehensive exploration of risks factors, impacts, and solutions

Salmonellosis, caused by Salmonella species, is one of the most common foodborne illnesses worldwide with an estimated 93.8 million cases and about 155,00 fatalities. In both industrialized and developing nations, Salmonellosis has been reported to be one of the most prevalent foodborne zoonoses and is linked with arrays of illness syndromes such as acute and chronic enteritis, and septicaemia. The two major and most common Salmonella species implicated in both warm-blooded and cold-blooded animals are Salmonella bongori and Salmonella enterica. To date, more than 2400 S. enterica serovars which affect both humans and animals have been identified. Salmonella is further classified into serotypes based on three primary antigenic determinants: somatic (O), flagella (H), and capsular (K). The capacity of nearly all Salmonella species to infect, multiply, and survive in human host cells with the aid of their pathogenic and virulence arsenals makes them deadly and important public health pathogens. Primarily, food-producing animals such as poultry, swine, cattle, and their products have been identified as important sources of salmonellosis. Additionally, raw fruits and vegetables are among other food types that have been linked to the spread of Salmonella spp. Based on the clinical manifestation of human salmonellosis, Salmonella strains can be categorized as either non-typhoidal Salmonella (NTS) and typhoidal Salmonella. The detection of aseptically collected Salmonella in necropsies, environmental samples, feedstuffs, rectal swabs, and food products serves as the basis for diagnosis. In developing nations, typhoid fever due to Salmonella Typhi typically results in the death of 5%-30% of those affected. The World Health Organization (WHO) calculated that there are between 16 and 17 million typhoid cases worldwide each year, with scaring 600,000 deaths as a result. The contagiousness of a Salmonella outbreak depends on the bacterial strain, serovar, growth environment, and host susceptibility. Risk factors for Salmonella infection include a variety of foods; for example, contaminated chicken, beef, and pork. Globally, there is a growing incidence and emergence of life-threatening clinical cases, especially due to multidrug-resistant (MDR) Salmonella spp, including strains exhibiting resistance to important antimicrobials such as beta-lactams, fluoroquinolones, and third-generation cephalosporins. In extreme cases, especially in situations involving very difficult-to-treat strains, death usually results. The severity of the infections resulting from Salmonella pathogens is dependent on the serovar type, host susceptibility, the type of bacterial strains, and growth environment. This review therefore aims to detail the nomenclature, etiology, history, pathogenesis, reservoir, clinical manifestations, diagnosis, epidemiology, transmission, risk factors, antimicrobial resistance, public health importance, economic impact, treatment, and control of salmonellosis.

Expression of Toll-like receptors and host defence peptides in the cecum of chicken challenged with Eimeria tenella

Chicken coccidiosis, caused by Eimeria protozoa, affects poultry farming. Toll-like receptors (TLRs) and host defence peptides (HDPs) help host innate immune responses to eliminate invading pathogens, but their roles in Eimeria tenella infection remain poorly understood. Herein, 14-day-old chickens were treated orally with 50,000 E. tenella oocysts and the cecum was dissected at different timepoints. mRNA expression of 10 chicken TLRs (chTLRs) and five HDPs was measured by quantitative real-time PCR. chTLR7 and chTLR15 were upregulated significantly at 3 h post-infection while other chTLRs were downregulated (p < .05). chTLR1a, chTLR1b, chTLR2b and chTLR4 peaked at 36 h post-infection, chTLR3, chTLR5 and chTLR15 peaked at 72 h post-infection and chTLR21 expression was highest among chTLRs, peaking at 48 h post-infection (p < 0.05). For HDPs, cathelicidin (CATH) 1 to 3 and B1 peaked at 48 h post-infection, liver-expressed antimicrobial peptide 2 peaked at 96 h post-infection, and CATH 2 expression was highest among HDPs. CATH2 and CATH3 were markedly upregulated at 3 h post-infection (p < .05). The results provide insight into innate immune molecules during E. tenella infection in chicken, and indicate that innate immune responses may mediate resistance to chicken coccidiosis.