Human Intestinal In Vitro Organ Culture as a Model for Investigation of Bacteria–Host Interactions

The Game for Three: Salmonella–Host–Microbiota Interaction Models

Colonization of the gastrointestinal (GI) tract by enteric pathogens occurs in a context strongly determined by host-specific gut microbiota, which can significantly affect the outcome of infection. The complex gameplay between the trillions of microbes that inhabit the GI tract, the host, and the infecting pathogen defines a specific triangle of interaction; therefore, a complete model of infection should consider all of these elements. Many different infection models have been developed to explain the complexity of these interactions. This review sheds light on current knowledge, along with the strengths and limitations of in vitro and in vivo models utilized in the study of Salmonella–host–microbiome interactions. These models range from the simplest experiment simulating environmental conditions using dedicated growth media through in vitro interaction with cell lines and 3-D organoid structure, and sophisticated “gut on a chip” systems, ending in various animal models. Finally, the challenges facing this field of research and the important future directions are outlined.

Development of a 3D printed device to support long term intestinal culture as an alternative to hyperoxic chamber methods

Background

Most interactions between pathogenic microorganisms and their target host occur on mucosal surfaces of internal organs such as the intestine. In vitro organ culture (IVOC) provides an unique tool for studying host-pathogen interactions in a controlled environment. However, this technique requires a complex laboratory setup and specialized apparatus. In addition, issues arise when anaerobic pathogens are exposed to the hyperoxic environment required for intestinal culture. The objective of this study was to develop an accessible 3D–printed device that would allow manipulation of the gas mixture used to supply the tissue culture media separately from the gas mixture exposed to the mucosal side of explants.

Results

Porcine colon explants from 2 pigs were prepared (n = 20) and cultured for 0h, 8h, 18h and 24h using the device. After the culture period, explants were fixed in formalin and H&E stained sections were evaluated for histological defects of the mucosa. At 8h, 66% of samples displayed no histological abnormalities, whereas samples collected at 18h and 24h displayed progressively increasing rates of superficial epithelial erosion and epithelial metaplasia.

Conclusions

The 3D–design reported here allows investigators to setup intestinal culture explants while manipulating the gas media explants are exposed to, to support tissue viability for a minimal of 8h. The amount of media necessary and tissue contamination are potential issues associated with this apparatus.

Electronic supplementary material

The online version of this article (10.1186/s41205-017-0018-z) contains supplementary material, which is available to authorized users.

Intestinal organoid as an in vitro model in studying host-microbial interactions

Background

Organoid is an in vitro three-dimensional organ-bud that shows realistic microanatomy and physiologic relevance. The progress in generating organoids that faithfully recapitulate human in vivo tissue composition has extended organoid applications from being just a basic research tool to a translational platform with a wide range of uses. Study of host-microbial interactions relies on model systems to mimic the in vivo infection. Researchers have developed various experimental models in vitro and in vivo to examine the dynamic host-microbial interactions. For some infectious pathogens, model systems are lacking whereas some of the used systems are far from optimal.

Objective

In the present work, we will review the brief history and recent findings using organoids for studying host-microbial interactions.

Methods

A systematic literature search was performed using the PubMed search engine. We also shared our data and research contribution to the field.

Results

we summarize the brief history of 3D organoids. We discuss the feasibility of using organoids in studying host-microbial interactions, focusing on the development of intestinal organoids and gastric organoids. We highlight the advantage and challenges of the new experimental models. Further, we discuss the future direction in using organoids in studying host-microbial interactions and its potential application in biomedical studies.

Conclusion

In combination with genetic, transcriptome and proteomic profiling, both murine- and human-derived organoids have revealed crucial aspects of development, homeostasis and diseases. Specifically, human organoids from susceptible host will be used to test their responses to pathogens, probiotics, and drugs. Organoid system is an exciting tool for studying infectious disease, microbiome, and therapy.

Nanoparticles for oral delivery: Design, evaluation and state-of-the-art

The oral route is a preferred method of drug administration, though achieving effective drug delivery and minimizing off-target side effects is often challenging. Formulation into nanoparticles can improve drug stability in the harsh gastrointestinal (GI) tract environment, providing opportunities for targeting specific sites in the GI tract, increasing drug solubility and bioavailability, and providing sustained release in the GI tract. However, the unique and diverse physiology throughout the GI tract, including wide variation in pH, mucus that varies in thickness and structure, numerous cell types, and various physiological functions are both a barrier to effective delivery and an opportunity for nanoparticle design. Here, nanoparticle design aspects to improve delivery to particular sites in the GI tract are discussed. We then review new methods for evaluating oral nanoparticle formulations, including a short commentary on data interpretation and translation. Finally, the state-of-the-art in preclinical targeted nanoparticle design is reviewed.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.