Development of the in vitro Cecal Chicken ALIMEntary tRact mOdel-2 to Study Microbiota Composition and Function

Application of Artificial Gastrointestinal Tract Models in Veterinary Medicine

Artificial gastrointestinal tract models have become essential tools in veterinary medicine, providing alternatives to in vivo studies, which are labor-intensive, costly, and under certain circumstances even ethically challenging. These in vitro models facilitate the study of digestion, enable disease and host-pathogen interaction modeling, and allow for the investigation of nutrient absorption, microbiota, and pharmacokinetics. Considering the One Health concept, the application of gastrointestinal tract systems in investigations for animals can clearly reflect human health, and thus, it is pointing to the relevance of the adaptation of already existing models and the development of new models to meet the needs of veterinary and animal farming practices. This review explores and compares the various types of gastrointestinal tract models, including static and dynamic systems, and their applications across different animal species. Specific technical and methodological considerations are discussed for core animal-developed and -tested artificial systems and their integration with common 'omics' techniques. Dynamic models, such as RUSITEC and PolyFermS, more accurately simulate in vivo processes, including peristalsis, enzymatic activity, and microbial fermentation. The studies employing tools for 'omics' approaches have been conducted with more understanding analysis and comprehensive discussion and results.

Exposure of broiler chickens to deoxynivalenol and Campylobacter jejuni induces substantial changes in intestinal gene expression

The mycotoxin deoxynivalenol (DON) is of high importance among feed contaminants because of its frequent occurrence in toxicologically relevant concentrations worldwide. Cereal crops, the main component of chicken diet, are commonly contaminated with DON, resulting in frequent exposure of chickens to DON. Likewise, Campylobacter (C.), a pathogen of major public and animal health concern, is frequently found in chicken flocks and poses a threat to the One Health approach. Campylobacter colonizes the gastrointestinal (GI) tract of poultry with a high bacterial load in the caeca. However, the mechanism of C. jejuni colonization in chickens is still not understood albeit it is well known that C. jejuni resides primarily in the mucosal layer of the chicken intestine. Therefore, in the actual study we focused on the effect of exposure to DON and/or C. jejuni on expression profiles of intestinal mucins (MUC1, MUC2), β-defensins (Gallinacin (GAL) 10, 12), cytokines (Toll-like receptor 2 (TLR2), Interleukin (IL) 6, 8, Interferon-γ (IFN)-γ), inducible nitric oxide synthase 2 (iNOS2), as well as selected tight junction proteins (Claudin 5 (CLDN5), Occludin (OCLN), and zonula occludens-1 (ZO1) via RT-qPCR. For this, a total of 150 one-day-old Ross 308 broiler chickens were randomly allocated to six different groups (n = 25 with 5 replicates/group) and were fed for 5 weeks with either contaminated diets (5 or 10 mg DON/kg feed) or basal diets (control). Following oral infection of birds with C. jejuni NCTC 12744 at 14 days of age, several changes in gene expression patterns were demonstrated. A significant (P ≤ 0.05) downregulation of MUC2 mRNA expression was observed in birds fed DON5 and DON10 diet, as well as in birds co-exposed to DON5 and C. jejuni at 7 dpi. Furthermore, at 14 dpi, MUC2 mRNA expression was significantly (P ≤ 0.05) downregulated in birds fed DON (5 mg and 10 mg/kg diet) with and without C. jejuni and in birds infected solely with C. jejuni. The actual study also demonstrated that co-exposure of broiler chickens to DON and C. jejuni resulted in a decreased barrier function via downregulation of OCLD mRNA expression. In addition, Campylobacter infection induced an increased expression of the antimicrobial peptide GAL12 and the IL8 gene, indicating that C. jejuni can initiate an immune response in the chicken gut in a proinflammatory manner. Similarly, DON with and without C. jejuni induced upregulation of GAL10 and GAL12 mRNA expression at 7 dpi. Moreover, no change in iNOS2 mRNA expression was observed in both the jejunum and the cecum at either 7 dpi or 14 dpi, suggesting unchanged NO production during exposure/infection. In conclusion, we confirmed that DON contamination corresponding to the currently applicable EU guidance value of 5 mg DON/kg feed affects the intestinal gene expression profiles of broilers, mainly in a dose-independent manner. Furthermore, DON exposure interacted synergistically with C. jejuni challenge regarding mucins, innate immunity gene expression in either the jejunum or the cecum, suggesting immunomodulatory activity of both foodborne agents (DON and C. jejuni).

Co-exposure to polyethylene fiber and Salmonella enterica serovar Typhimurium alters microbiome and metabolome of in vitro chicken cecal mesocosms

Humans and animals encounter a summation of exposures during their lifetime (the exposome). In recent years, the scope of the exposome has begun to include microplastics. Microplastics (MPs) have increasingly been found in locations, including in animal gastrointestinal tracts, where there could be an interaction with Salmonella enterica serovar Typhimurium, one of the commonly isolated serovars from processed chicken. However, there is limited knowledge on how gut microbiomes are affected by microplastics and if an effect would be exacerbated by the presence of a pathogen. In this study, we aimed to determine if acute exposure to microplastics in vitro altered the gut microbiome membership and activity. The microbiota response to a 24 h co-exposure to Salmonella enterica serovar Typhimurium and/or low-density polyethylene (PE) microplastics in an in vitro broiler cecal model was determined using 16S rRNA amplicon sequencing (Illumina) and untargeted metabolomics. Community sequencing results indicated that PE fiber with and without S. Typhimurium yielded a lower Firmicutes/Bacteroides ratio compared with other treatment groups, which is associated with poor gut health, and overall had greater changes to the cecal microbial community composition. However, changes in the total metabolome were primarily driven by the presence of S. Typhimurium. Additionally, the co-exposure to PE fiber and S. Typhimurium caused greater cecal microbial community and metabolome changes than either exposure alone. Our results indicate that polymer shape is an important factor in effects resulting from exposure. It also demonstrates that microplastic-pathogen interactions cause metabolic alterations to the chicken cecal microbiome in an in vitro chicken cecal mesocosm.

IMPORTANCE

Researching the exposome, a summation of exposure to one's lifespan, will aid in determining the environmental factors that contribute to disease states. There is an emerging concern that microplastic-pathogen interactions in the gastrointestinal tract of broiler chickens may lead to an increase in Salmonella infection across flocks and eventually increased incidence of human salmonellosis cases. In this research article, we elucidated the effects of acute co-exposure to polyethylene microplastics and Salmonella enterica serovar Typhimurium on the ceca microbial community in vitro. Salmonella presence caused strong shifts in the cecal metabolome but not the microbiome. The inverse was true for polyethylene fiber. Polyethylene powder had almost no effect. The co-exposure had worse effects than either alone. This demonstrates that exposure effects to the gut microbial community are contaminant-specific. When combined, the interactions between exposures exacerbate changes to the gut environment, necessitating future experiments studying low-dose chronic exposure effects with in vivo model systems.

Modulation of Poultry Cecal Microbiota by a Phytogenic Blend and High Concentrations of Casein in a Validated In Vitro Cecal Chicken Alimentary Tract Model

Phytogenic blends (PBs) consist of various bioactive plant-derived compounds that are used as growth promoters for farm animals. Feed additives based on PBs have beneficial effects on farm animals' production performance, health, and overall well-being, as well as positive modulating effects on gut microbiota. In this study, we used a validated in vitro cecal chicken alimentary tract model (CALIMERO-2) to evaluate the effects of a PB (a mix of components found in rosemary, cinnamon, curcuma, oregano oil, and red pepper), alone or in combination with casein (control), on poultry cecal microbiota. Supplementation with the PB significantly increased the abundance of bacteria associated with energy metabolism (Monoglobus) and growth performance in poultry (Lachnospiraceae UCG-010). The PB also decreased the abundance of opportunistic pathogens (Escherichia-Shigella) and, most importantly, did not promote other opportunistic pathogens, which indicates the safety of this blend for poultry. In conclusion, the results of this study show promising perspectives on using PBs as feed additives for poultry, although further in vivo studies need to prove these data.

Response of laying hens fed diet supplemented with a mixture of olive, laurel, and rosemary leaf powders: Metabolic profile, oxidative status, intestinal histomorphology, and egg quality

This study aimed to evaluate the effects of a mixture of olive, laurel, and rosemary leaf powders, on the oxidative state, biochemical, immune, intestinal morphophysiological parameters, and egg quality of laying hens. One hundred Lohmann Brown hens (28 weeks old) were equally assigned to two groups (n. 50) corresponding to a basal control diet (CON) or the diet supplemented with 6 g/kg feed of leaf powder mixture (LPM) containing olive, laurel, and rosemary leaves (1:1:1), for 60 days. Oxidative status, biochemical indices, immune response, cecal short chain fatty acids (SCFAs), intestinal morphological characteristics, and some egg traits were evaluated at the end of the experiment. The results indicated that LPM improved (P < 0.05) the oxidative status (TOS, ROMs), the immune system (IL-6, IL-1β, and TNF-α), the total protein and HDL cholesterol content, whereas it decreased (P < 0.05) total cholesterol and LDL cholesterol. Aspartate aminotransferase (AST), alkaline phosphatase (ALP), and alanine aminotransferase were significantly (P < 0.05) lower in the LPM than in the CON group. A significant increase (P < 0.05) in SCFA content in the caecum, as well as in villi height and crypt depth in both duodenum and ileum of LPM-treated hens, was observed. Egg quality parameters were not influenced (P > 0.05) by LPM. These findings indicate that LPM can be considered a candidate as an antioxidant ingredient for functional food in laying hens.

An In Vitro Model of the Chicken Gastrointestinal Tract with Special Emphasis to the Cecal Microbiota

An in vitro model of the upper gastrointestinal tract as well as the chicken cecum was developed to have a predictive tool for estimating the production performance of animals by analyzing the feeding value of a certain diet. The upper gastrointestinal tract consists of a batch type model, whereas the cecal model is comprised of 4 semi-continuous connected vessels inoculated with cecal or fecal microbes. The upper gastrointestinal tract and cecal simulations were both run with a corn- and a wheat-based diet to simulate 2 typical feed types. Samples were collected after the 5-h cecal simulations and aliquots were frozen to assess inoculum stability. The microbiota was analyzed by 16S rRNA gene sequencing, whereas short chain fatty acids as microbial metabolites were analyzed by using gas chromatography. As expected, some significant differences in microbial abundance after simulation between the cecal and fecal slurry samples (P = 0.001) were detected, as well between the fresh and frozen status (P = 0.001), hence simulations inoculated with cecal and fresh samples being more diverse. For the measured metabolites, almost all of them increased (P < 0.05) significantly when comparing fresh and frozen inoculum. The present chicken intestinal in vitro model represents a rapid systematic screening system for studying dietary related microbial changes and reducing the need of animal sacrifice for experimentation.

Long-term hexavalent chromium exposure disturbs the gut microbial homeostasis of chickens

Industrial production, ore smelting and sewage disposal plant can discharge large amounts of heavy metals every year, which may contaminate soil, water and air, posing a great threat to ecological environment and animal production. Hexavalent chromium [Cr (VI)], a recognized metallic contaminant, has been shown to impair kidney, liver and gastrointestinal tract of many species, but little is known about the gut microbial characteristics of chickens exposed to Cr (VI). Herein, this study characterized the gut microbial alternations of chickens exposed to Cr (VI). Results indicated that the gut microbial alpha-diversity in chickens exposed to Cr (VI) decreased significantly, accompanied by a distinct shifts in taxonomic composition. Microbial taxonomic analysis demonstrated that the preponderant phyla (Firmicutes, Bacteroidetes, Proteobacteria and Epsilonbacteraeota) were the same in both groups, but different in types and relative abundances of dominant genera. Moreover, some bacterial taxa including 2 phyla and 47 genera significantly decreased, whereas 3 phyla and 17 genera significantly increased during Cr (VI) exposure. Among decreased taxa, 9 genera (Coprobacter, Ruminococcus_1, Faecalicoccus, Eubacterium_nodatum_group, Parasutterella, Slackia, Barnesiella, Family_XIII_UCG-001 and Collinsella) even cannot be detected. In conclusion, this study revealed that Cr (VI) exposure dramatically decrased the gut microbial diversity and altered microbial composition of chickens. Additionally, this study also provided a theoretical basis for relieving Cr (VI) poisoning from the perspective of gut microbiota.

In vitro Modeling of Chicken Cecal Microbiota Ecology and Metabolism Using the PolyFermS Platform

Continuous in vitro fermentation models provide a useful tool for a fast, reproducible, and direct assessment of treatment-related changes in microbiota metabolism and composition independent of the host. In this study, we used the PolyFermS model to mimic the conditions of the chicken cecum and evaluated three nutritive media for in vitro modeling of the chicken cecal microbiota ecology and metabolism. We observed that our model inoculated with immobilized cecal microbiota and fed with a modified Viande Levure medium (mVL-3) reached a high bacterial cell density of up to approximately 10.5 log cells per mL and stable microbiota composition, akin to the host, during 82 days of continuous operation. Relevant bacterial functional groups containing primary fibrolytic (Bacteroides, Bifidobacteriaceae, Ruminococcaceae), glycolytic (Enterococcus), mucolytic (Bacteroides), proteolytic (Bacteroides), and secondary acetate-utilizing butyrate-producing and propionate-producing (Lachnospiraceae) taxa were preserved in vitro. Besides, conserved metabolic and functional Kyoto Encyclopedia of Genes and Genomes pathways were observed between in vitro microbiota and cecal inoculum microbiota as predicted by functional metagenomics analysis. Furthermore, we demonstrated that the continuous inoculation provided by the inoculum reactor generated reproducible metabolic profiles in second-stage reactors comparable to the chicken cecum, allowing for the simultaneous investigation and direct comparison of different treatments with a control. In conclusion, we showed that PolyFermS is a suitable model for mimicking chicken cecal microbiota fermentation allowing ethical and ex vivo screening of environmental factors, such as dietary additives, on chicken cecal fermentation. We report here for the first time a fermentation medium (mVL-3) that closely mimics the substrate conditions in the chicken cecum and supports the growth and metabolic activity of the cecal bacterial akin to the host. Our PolyFermS chicken cecum model is a useful tool to study microbiota functionality and structure ex vivo.

The Interplay between Salmonella and Intestinal Innate Immune Cells in Chickens

Salmonellosis is a common infection in poultry, which results in huge economic losses in the poultry industry. At the same time, Salmonella infections are a threat to public health, since contaminated poultry products can lead to zoonotic infections. Antibiotics as feed additives have proven to be an effective prophylactic option to control Salmonella infections, but due to resistance issues in humans and animals, the use of antimicrobials in food animals has been banned in Europe. Hence, there is an urgent need to look for alternative strategies that can protect poultry against Salmonella infections. One such alternative could be to strengthen the innate immune system in young chickens in order to prevent early life infections. This can be achieved by administration of immune modulating molecules that target innate immune cells, for example via feed, or by in-ovo applications. We aimed to review the innate immune system in the chicken intestine; the main site of Salmonella entrance, and its responsiveness to Salmonella infection. Identifying the most important players in the innate immune response in the intestine is a first step in designing targeted approaches for immune modulation.