Research in a time of enteroids and organoids: how the human gut model has transformed the study of enteric bacterial pathogens

Organoids in gastrointestinal diseases: from bench to clinic

The etiology of gastrointestinal (GI) diseases is intricate and multifactorial, encompassing complex interactions between genetic predisposition and gut microbiota. The cell fate change, immune function regulation, and microenvironment composition in diseased tissues are governed by microorganisms and mutated genes either independently or through synergistic interactions. A comprehensive understanding of GI disease etiology is imperative for developing precise prevention and treatment strategies. However, the existing models used for studying the microenvironment in GI diseases-whether cancer cell lines or mouse models-exhibit significant limitations, which leads to the prosperity of organoids models. This review first describes the development history of organoids models, followed by a detailed demonstration of organoids application from bench to clinic. As for bench utilization, we present a layer-by-layer elucidation of organoid simulation on host-microbial interactions, as well as the application in molecular mechanism analysis. As for clinical adhibition, we provide a generalized interpretation of organoid application in GI disease simulation from inflammatory disorders to malignancy diseases, as well as in GI disease treatment including drug screening, immunotherapy, and microbial-targeting and screening treatment. This review draws a comprehensive and systematical depiction of organoids models, providing a novel insight into the utilization of organoids models from bench to clinic.

Colonization factors of human and animal-specific enterotoxigenic Escherichia coli (ETEC)

Colonization factors (CFs) are major virulence factors of enterotoxigenic Escherichia coli (ETEC). This pathogen is among the most common causes of bacterial diarrhea in children in low- and middle-income countries, travelers, and livestock. CFs are major candidate antigens in vaccines under development as preventive measures against ETEC infections in humans and livestock. Recent molecular studies have indicated that newly identified CFs on human ETEC are closely related to animal ETEC CFs. Increased knowledge of pathogenic mechanisms, immunogenicity, regulation, and expression of ETEC CFs, as well as the possible spread of animal ETEC to humans, may facilitate the future development of ETEC vaccines for humans and animals. Here, we present an updated review of CFs in ETEC.

Advancements in understanding bacterial enteritis pathogenesis through organoids

Bacterial enteritis has a substantial role in contributing to a large portion of the global disease burden and serves as a major cause of newborn mortality. Despite advancements gained from current animal and cell models in improving our understanding of pathogens, their widespread application is hindered by apparent drawbacks. Therefore, more precise models are imperatively required to develop more accurate studies on host-pathogen interactions and drug discovery. Since the emergence of intestinal organoids, massive studies utilizing organoids have been conducted to study the pathogenesis of bacterial enteritis, revealing new mechanisms and validating established ones. In this review, we focus on the advancements of several bacterial pathogenesis mechanisms observed in intestinal organoid/enteroid models, exploring the host response and bacterial effectors during the infection process. Finally, we address the features that warrant additional investigation or could be enhanced in existing organoid models in order to guide future research endeavors.

Translocation across a human enteroid monolayer by zoonotic Streptococcus suis correlates with the presence of Gb3-positive cells

Streptococcus suis is a zoonotic pathogen that can cause meningitis and septicaemia. The consumption of undercooked pig products is an important risk factor for zoonotic infections, suggesting an oral route of infection. In a human enteroid model, we show that the zoonotic CC1 genotype has a 40% higher translocation frequency than the non-zoonotic CC16 genotype. Translocation occurred without increasing the permeability or disrupting the adherens junctions and tight junctions of the epithelial monolayer. The translocation of zoonotic S. suis was correlated with the presence of Gb3-positive cells, a human glycolipid receptor found on Paneth cells and targeted by multiple enteric pathogens. The virulence factors Streptococcal adhesin Protein and suilysin, known to interact with Gb3, were not essential for translocation in our epithelial model. Thus, the ability to translocate across an enteroid monolayer correlates with S. suis core genome composition and the presence of Gb3-positive cells in the intestinal epithelium.

Cholera intoxication of human enteroids reveals interplay between decoy and functional glycoconjugate ligands

Prior research on cholera toxin (CT) binding and intoxication has relied on human colonic cancer derived epithelial cells. While these transformed cell lines have been beneficial, they neither derive from small intestine where intoxication occurs, nor represent the diversity of small intestinal epithelial cells (SI-ECs) and variation in glycoconjugate expression among individuals. Here, we used human enteroids, derived from jejunal biopsies of multipledonors to study CT binding and intoxication of human non-transformed SI-ECs. We modulated surface expression of glycosphingolipids, glycoproteins and specific glycans to distinguish the role of each glycan/glycoconjugate. Cholera-toxin-subunit-B (CTB) mutants were generated to decipher the preference of each glycoconjugate to different binding sites and the correlation between CT binding and intoxication. Human enteroids contain trace amounts of GM1, but other glycosphingolipids may be contributing to CT intoxication. We discovered that inhibition of either fucosylation or O-glycosylation sensitize enteroids to CT-intoxication. This can either be a consequence of the removal of fucosylated "decoy-like-ligands" binding to CTB's non-canonical site and/or increase in the availability of Gal/GalNAc-terminating glycoconjugates binding to the canonical site. Furthermore, simultaneous inhibition of fucosylation and O-glycosylation increased the availability of additional Gal/GalNAc-terminating glycoconjugates but counteracted the sensitization in CT intoxication caused by inhibiting O-glycosylation because of reduction in fucose. This implies a dual role of fucose as a functional glycan and a decoy, the interplay of which influences CT binding and intoxication. Finally, while the results were similar for enteroids from different donors, they were not identical, pointing to a role for human genetic variation in determining sensitivity to CT.

The role of the minor colonization factor CS14 in adherence to intestinal cell models by geographically diverse ETEC isolates

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low- to middle-income countries. ETEC adheres to small intestinal epithelia via colonization factors (CFs) and secretes heat-stable toxin and/or heat-labile toxin, causing dysregulated ion transport and water secretion. There are over 30 CFs identified, including major CFs associated with moderate-to-severe diarrhea (MSD) and minor CFs for which a role in pathogenesis is less clear. The Global Enteric Multicenter Study identified CS14, a class 5a fimbriae, as the only minor CF significantly associated with MSD and was recommended for inclusion in ETEC vaccines. Despite detection of CS14 in ETEC isolates, the sequence conservation of the CS14 operon, its role in adherence, and functional cross-reactivity to other class 5a fimbriae like CFA/I and CS4 are not understood. Sequence analysis determined that the CS14 operon is >99.9% identical among seven geographically diverse isolates with expanded sequence analysis demonstrating SNPs exclusively in the gene encoding the tip adhesin CsuD. Western blots and electron microscopy demonstrated that CS14 expression required the growth of isolates on CFA agar with the iron chelator deferoxamine mesylate. CS14 expression resulted in significantly increased adherence to cultured intestinal cells and human enteroids. Anti-CS14 antibodies and anti-CS4 antibodies, but not anti-CFA/I antibodies, inhibited the adherence of a subset of ETEC isolates, demonstrating CS14-specific inhibition with partial cross-reactivity within the class 5a fimbrial family. These data provide support for CS14 as an important fimbrial CF and its consideration as a vaccine antigen in future strategies. IMPORTANCE Enterotoxigenic Escherichia coli (ETEC) infection causes profuse watery diarrhea in adults and children in low- to middle-income countries and is a leading cause of traveler's diarrhea. Despite increased use of rehydration therapies, young children especially can suffer long-term effects including gastrointestinal dysfunction as well as stunting and malnutrition. As there is no licensed vaccine for ETEC, there remains a need to identify and understand specific antigens for inclusion in vaccine strategies. This study investigated one adhesin named CS14. This adhesin is expressed on the bacterial surface of ETEC isolates and was recently recognized for its significant association with diarrheal disease. We demonstrated that CS14 plays a role in bacterial adhesion to human target cells, a critical first step in the disease process, and that adherence could be blocked by CS14-specific antibodies. This work will significantly impact the ETEC field by supporting inclusion of CS14 as an antigen for ETEC vaccines.

The metabolic impact of bacterial infection in the gut

Bacterial infections of the gut are one of the major causes of morbidity and mortality worldwide. The interplay between the pathogen and the host is finely balanced, with the bacteria evolving to proliferate and establish infection. In contrast, the host mounts a response to first restrict and then eliminate the infection. The intestine is a rapidly proliferating tissue, and metabolism is tuned to cater to the demands of proliferation and differentiation along the crypt-villus axis (CVA) in the gut. As bacterial pathogens encounter the intestinal epithelium, they elicit changes in the host cell, and core metabolic pathways such as the tricarboxylic acid (TCA) cycle, lipid metabolism and glycolysis are affected. This review highlights the mechanisms utilized by diverse gut bacterial pathogens to subvert host metabolism and describes host responses to the infection.

Bugs and the barrier: A review of the gut microbiome and intestinal barrier in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease that affects premature neonates. It frequently results in significant morbidity and mortality for those affected. Years of research into the pathophysiology of NEC have revealed it to be a variable and multifactorial disease. However, there are risk factors associated with NEC including low birth weight, prematurity, intestinal immaturity, alterations in microbial colonization, and history of rapid or formula based enteral feeds (Fig. 1).^1-3 An accepted generalization of the pathogenesis of NEC includes a hyperresponsive immune reaction to insults such as ischemia, starting formula feeds, or alterations in the microbiome with pathologic bacterial colonization and translocation. This reaction causes a hyperinflammatory response disrupting the normal intestinal barrier, allowing abnormal bacterial translocation and ultimately sepsis.^1,2,4 This review will focus specifically on the interactions with the microbiome and intestinal barrier function in NEC.

Apical-Out Enteroids as an Innovative Model for Necrotizing Enterocolitis

INTRODUCTION

Necrotizing enterocolitis (NEC) is a gastrointestinal disease of premature neonates. We previously validated a NEC enteroid model derived from human infant intestinal tissue. Typical enteroid configuration is basolateral-out (BO) without direct access to the luminal (apical) surface. Apical access is necessary to allow physiologic comparison of pathogen interaction with the intestinal epithelial barrier. We hypothesize that apical-out (AO) enteroids will provide a relevant NEC model to study this relationship.

METHODS

Following the institutional review board approval (#11610-11611), neonatal intestinal tissue was collected from surgical specimens. Stem cells were collected; enteroids were generated and grown to maturity in BO conformation then everted to AO. Enteroids were untreated or treated for 24 h with 100 μg/mL lipopolysaccharide and hypoxia. Protein and gene expression were analyzed for inflammatory markers, tight junction (TJ) proteins and permeability characteristic of NEC.

RESULTS

Apical TJ protein zonula occludens-1 and basolateral protein β-catenin immunofluorescence confirmed AO configuration. Treated AO enteroids had significantly increased messenger RNA (P = 0.001) and protein levels (P < 0.0001) of tumor necrosis factor-α compared to controls. Corrected total cell fluorescence of toll-like receptor 4 was significantly increased in treated AO enteroids compared to control (P = 0.002). Occludin was found to have significantly decreased messenger RNA in treated AO enteroids (P = 0.003). Expression of other TJ proteins claudins-1, -4 and zonula occludens-1 was significantly decreased in treated AO enteroids (P < 0.05).

CONCLUSIONS

AO enteroids present an innovative model for NEC with increased inflammation and gut barrier restructuring. This model allows for a biologically relevant investigation of the interaction between the pathogen and the intestinal epithelial barrier in NEC.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

In-depth analysis of the relationship between bovine intestinal organoids and enteroids based on morphology and transcriptome

Intestinal organoids and enteroids as excellent models are miniaturized and simplified for studying intestinal physiological and pathological functions, drug screening, and regenerative medicine. Recently, the application demands for organoids and enteroids in organ development and nutrition metabolism, immune and cancer research increased. But there are few comparative studies on both of them, especially in immunity and metabolism, which is also conducive to further clarifying the role of crypt stem cells and stromal cells. In our study, "natural" organoids were obtained by tissue culture from fetal bovine jejunum and enteroids were successfully isolated and cultured from organoids without supplementing exogenous factors and Matrigel. These mini-guts displayed similar features to the intestine through immunohistochemistry and transmission electron microscopy. Organoid and enteroid were systematically compared based on the transcriptome. And some of the results were verified by qRT-PCR. Our results showed KDGs (Key driver genes) (e.g., SLC13A1, HOXA7, HOXA6, HOXA5, and HOXD4) of organoids enriched in signaling pathways related to organ development and morphology and metabolism. KDGs (e.g., IL-6, PTGS2, CDH1, JUN, and EGFR) of enteroid were involved in cancer, MAPK, and immune-related signaling pathways. To the Wnt signaling pathway, highly expressed genes in organoids, including RSPO2, NOTUM, WNT6, and RSPO3, supported the homeostasis of crypt stem cells. Enteroids highly expressed CTNNB1 and WNTs. In addition, we found that organoids and enteroids carried out different functions in immunity and metabolism due to different cell compositions. Therefore, it suggested organoid is more compatible and comprehensive, and enteroid is qualified for the research of immunity and cancer.

Gut microbiome and aging nexus and underlying mechanism

According to the United Nations population profile, the number of individuals aged 60 and over in high-income nations is expected to rise from 302 million to over 366 million between 2019 and 2030, so there is an increasing emphasis on nutrition and health in older people. Numerous studies have demonstrated the crucial role that gut microbiota plays in maintaining human health. As a model of healthy aging, centenarians have different gut microbiota from ordinary elderly people. The core microbiome of centenarians in various countries has shown some common characteristics, which are worth further exploration. In this review, the significance of the human gut microbiota to health is briefly discussed, and the characteristics of the gut microbiota of long-lived senior persons of different ages and in different countries are described. Moreover, this review lists dietary interventions and fecal microbiota transplantation. In the end, it discusses the pros and cons of using probiotics to enhance the health of seniors through focused management of the gut microbiota. It aims to pave the way for further investigation into the nexus between gut microbiota, probiotics, and longevity, and then to reveal the underlying mechanism to promote longevity. KEY POINTS: • Gut microbial structure in different age groups and the characteristics of gut microbiota in centenarians. • Dietary interventions, fecal transplants, and probiotics target the modulation of gut microbiota for healthy aging.

The role of CFA/I in adherence and toxin delivery by ETEC expressing multiple colonization factors in the human enteroid model

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low-to-middle-income countries (LMICs). ETEC adhere to intestinal epithelia via colonization factors (CFs) and secrete heat-stable toxin (ST) and/or heat-labile toxin (LT), causing dysregulated cellular ion transport and water secretion. ETEC isolates often harbor genes encoding more than one CF that are targets as vaccine antigens. CFA/I is a major CF that is associated with ETEC that causes moderate-to-severe diarrhea and plays an important role in pathogenesis. The Global Enteric Multicenter Study finding that 78% of CFA/I-expressing ETEC also encode the minor CF CS21 prompted investigation of the combined role of these two CFs. Western blots and electron microscopy demonstrated growth media-dependent and strain-dependent differences in CFA/I and CS21 expression. The critical role of CFA/I in adherence by ETEC strains expressing CFA/I and CS21 was demonstrated using the human enteroid model and a series of CFA/I- and CS21-specific mutants. Furthermore, only anti-CFA/I antibodies inhibited adherence by global ETEC isolates expressing CFA/I and CS21. Delivery of ST and resulting cGMP secretion was measured in supernatants from infected enteroid monolayers, and strain-specific ST delivery and time-dependent cGMP production was observed. Interestingly, cGMP levels were similar across wildtype and CF-deficient strains, reflecting a limitation of this static aerobic infection model. Despite adherence by ETEC and delivery of ST, the enteroid monolayer integrity was not disrupted, as shown by the lack of decrease in transepithelial electrical resistance and the lack of IL-8 cytokines produced during infection. Taken together, these data demonstrate that targeting CFA/I in global clinical CFA/I-CS21 strains is sufficient for adherence inhibition, supporting a vaccine strategy that focuses on blocking major CFs. In addition, the human enteroid model has significant utility for the study of ETEC pathogenesis and evaluation of vaccine-induced functional antibody responses.

Interactions between Enterohemorrhagic Escherichia coli (EHEC) and Gut Commensals at the Interface of Human Colonoids

The interactions between the gut microbiota and pathogens are complex and can determine the outcome of an infection. Enterohemorrhagic Escherichia coli (EHEC) is a major human enteric pathogen that colonizes the colon through attaching and effacing (AE) lesions and uses microbiota-derived molecules as cues to control its virulence. Different gut commensals can modulate EHEC virulence. However, the lack of an animal model that recapitulates the human pathophysiology of EHEC infection makes it challenging to investigate how variations in microbiota composition could affect host susceptibility to this pathogen. Here, we addressed these interactions building from simple to more complex in vitro systems, culminating with the use of the physiological relevant human colonoids as a model to study the interactions between EHEC and different gut commensals. We demonstrated that Bacteroides thetaiotaomicron and Enterococcus faecalis enhance virulence expression and AE lesion formation in cultured epithelial cells, as well as on the colonic epithelium, while commensal E. coli did not affect these phenotypes. Importantly, in the presence of these three commensals together, virulence and AE lesion are enhanced. Moreover, we identified specific changes in the metabolic landscape promoted by different members of the gut microbiota and showed that soluble factors released by E. faecalis can increase EHEC virulence gene expression. Our study highlights the importance of interspecies bacterial interactions and chemical exchange in the modulation of EHEC virulence. IMPORTANCE Enterohemorrhagic E. coli (EHEC) is a natural human pathogen that poorly colonizes mice. Hence, the use of murine models to understand features of EHEC infection is a challenge. In this study, we use human colonoids as a physiologically relevant model to study interactions between EHEC and gut commensals. We demonstrate that the ability of EHEC to form AE lesions on the intestinal epithelium is enhanced by the presence of certain gut commensals, such as B. thetaiotaomicron and E. faecalis, while it is not affected by commensal E. coli. Furthermore, we show that commensal bacteria differently impact the metabolic landscape. These data suggest that microbiota compositions can differentially modulate EHEC-mediated disease.

TMT-Based Quantitative Proteomic Analysis of Intestinal Organoids Infected by Listeria monocytogenes Strains with Different Virulence

L. monocytogenes, consisting of 13 serotypes, is an opportunistic food-borne pathogen that causes different host reactions depending on its serotypes. In this study, highly toxic L. monocytogenes 10403s resulted in more severe infections and lower survival rates. Additionally, to investigate the remodeling of the host proteome by strains exhibiting differential toxicity, the cellular protein responses of intestinal organoids were analyzed using tandem mass tag (TMT) labeling and high-performance liquid chromatography−mass spectrometry. The virulent strain 10403s caused 102 up-regulated and 52 down-regulated proteins, while the low virulent strain M7 caused 188 up-regulated and 25 down-regulated proteins. Based on the analysis of gene ontology (GO) and KEGG databases, the expressions of differential proteins in organoids infected by L. monocytogenes 10403s (virulent strain) or M7 (low virulent strain) were involved in regulating essential processes such as the biological metabolism, the energy metabolism, and immune system processes. The results showed that the immune system process, as the primary host defense response to L. monocytogenes, comprised five pathways, including ECM−receptor interaction, the complement and coagulation cascades, HIF-1, ferroptosis, and NOD-like receptor signaling pathways. As for the L. monocytogenes 10403s vs. M7 group, the expression of differential proteins was involved in two pathways: systemic lupus erythematosus and transcriptional mis-regulation in cancer. All in all, these results revealed that L. monocytogenes strains with different toxicity induced similar biological functions and immune responses while having different regulations on differential proteins in the pathway.

Shigella-Controlled Human Infection Models: Current and Future Perspectives

Shigella-controlled human infection models (CHIMs) are an invaluable tool utilized by the vaccine community to combat one of the leading global causes of infectious diarrhea, which affects infants, children and adults regardless of socioeconomic status. The impact of shigellosis disproportionately affects children in low- and middle-income countries (LMICs) resulting in cognitive and physical stunting, perpetuating a cycle that must be halted. Shigella-CHIMs not only facilitate the early evaluation of enteric countermeasures and up-selection of the most promising products but also provide insight into mechanisms of infection and immunity that are not possible utilizing animal models or in vitro systems. The greater understanding of shigellosis obtained in CHIMs builds and empowers the development of new generation solutions to global health issues which are unattainable in the conventional laboratory and clinical settings. Therefore, refining, mining and expansion of safe and reproducible infection models hold the potential to create effective means to end diarrheal disease and associated co-morbidities associated with Shigella infection.

Transcytosis of IgA Attenuates Salmonella Invasion in Human Enteroids and Intestinal Organoids

Secretory IgA (SIgA) is the most abundant antibody type in intestinal secretions where it contributes to safeguarding the epithelium from invasive pathogens like the Gram-negative bacterium, Salmonella enterica serovar Typhimurium (STm). For example, we recently reported that passive oral administration of the recombinant monoclonal SIgA antibody, Sal4, to mice promotes STm agglutination in the intestinal lumen and restricts bacterial invasion of Peyer's patch tissues. In this report, we sought to recapitulate Sal4-mediated protection against STm in human Enteroids and human intestinal organoids (HIOs) as models to decipher the molecular mechanisms by which antibodies function in mucosal immunity in the human gastrointestinal tract. We confirm that Enteroids and HIO-derived monolayers are permissive to STm infection, dependent on HilD, the master transcriptional regulator of the SPI-I type three secretion system (T3SS). Stimulation of M-like cells in both Enteroids and HIOs by the addition of RANKL further enhanced STm invasion. The apical addition of Sal4 mouse IgA, as well as recombinant human Sal4 dimeric IgA (dIgA) and SIgA resulted a dose-dependent reduction in bacterial invasion. Moreover, basolateral application of Sal4 dIgA to Enteroid and HIO monolayers gave rise to SIgA in the apical compartment via a pathway dependent on expression of the polymeric immunoglobulin receptor (pIgR). The resulting Sal4 SIgA was sufficient to reduce STm invasion of Enteroid and HIO epithelial cell monolayers by ~20-fold. Recombinant Sal4 IgG was also transported in the Enteroid and HIOs, but to a lesser degree and via a pathway dependent on the neonatal Fc receptor (FCGRT). The models described lay the foundation for future studies into detailed mechanisms of IgA and IgG protection against STm and other pathogens.

Yersinia pseudotuberculosis YopE prevents uptake by M cells and instigates M cell extrusion in human ileal enteroid-derived monolayers

Many pathogens use M cells to access the underlying Peyer's patches and spread to systemic sites via the lymph as demonstrated by ligated loop murine intestinal models. However, the study of interactions between M cells and microbial pathogens has stalled due to the lack of cell culture systems. To overcome this obstacle, we use human ileal enteroid-derived monolayers containing five intestinal cell types including M cells to study the interactions between the enteric pathogen, Yersinia pseudotuberculosis (Yptb), and M cells. The Yptb type three secretion system (T3SS) effector Yops inhibit host defenses including phagocytosis and are critical for colonization of the intestine and Peyer's patches. Therefore, it is not understood how Yptb traverses through M cells to breach the epithelium. By growing Yptb under two physiological conditions that mimic the early infectious stage (low T3SS-expression) or host-adapted stage (high T3SS-expression), we found that large numbers of Yptb specifically associated with M cells, recapitulating murine studies. Transcytosis through M cells was significantly higher by Yptb expressing low levels of T3SS, because YopE and YopH prevented Yptb uptake. YopE also caused M cells to extrude from the epithelium without inducing cell-death or disrupting monolayer integrity. Sequential infection with early infectious stage Yptb reduced host-adapted Yptb association with M cells. These data underscore the strength of enteroids as a model by discovering that Yops impede M cell function, indicating that early infectious stage Yptb more effectively penetrates M cells while the host may defend against M cell penetration of host-adapted Yptb.

A Versatile Human Intestinal Organoid-Derived Epithelial Monolayer Model for the Study of Enteric Pathogens

Gastrointestinal infections cause significant morbidity and mortality worldwide. The complexity of human biology and limited insights into host-specific infection mechanisms are key barriers to current therapeutic development. Here, we demonstrate that two-dimensional epithelial monolayers derived from human intestinal organoids, combined with in vivo-like bacterial culturing conditions, provide significant advancements for the study of enteropathogens. Monolayers from the terminal ileum, cecum, and ascending colon recapitulated the composition of the gastrointestinal epithelium, in which several techniques were used to detect the presence of enterocytes, mucus-producing goblet cells, and other cell types following differentiation. Importantly, the addition of receptor activator of nuclear factor kappa-B ligand (RANKL) increased the presence of M cells, critical antigen-sampling cells often exploited by enteric pathogens. For infections, bacteria were grown under in vivo-like conditions known to induce virulence. Overall, interesting patterns of tissue tropism and clinical manifestations were observed. Shigella flexneri adhered efficiently to the cecum and colon; however, invasion in the colon was best following RANKL treatment. Both Salmonella enterica serovars Typhi and Typhimurium displayed different infection patterns, with S. Typhimurium causing more destruction of the terminal ileum and S. Typhi infecting the cecum more efficiently than the ileum, particularly with regard to adherence. Finally, various pathovars of Escherichia coli validated the model by confirming only adherence was observed with these strains. This work demonstrates that the combination of human-derived tissue with targeted bacterial growth conditions enables powerful analyses of human-specific infections that could lead to important insights into pathogenesis and accelerate future vaccine development. IMPORTANCE While traditional laboratory techniques and animal models have provided valuable knowledge in discerning virulence mechanisms of enteric pathogens, the complexity of the human gastrointestinal tract has hindered our understanding of physiologically relevant, human-specific interactions; and thus, has significantly delayed successful vaccine development. The human intestinal organoid-derived epithelial monolayer (HIODEM) model closely recapitulates the diverse cell populations of the intestine, allowing for the study of human-specific infections. Differentiation conditions permit the expansion of various cell populations, including M cells that are vital to immune recognition and the establishment of infection by some bacteria. We provide details of reproducible culture methods and infection conditions for the analyses of Shigella, Salmonella, and pathogenic Escherichia coli in which tissue tropism and pathogen-specific infection patterns were detected. This system will be vital for future studies that explore infection conditions, health status, or epigenetic differences and will serve as a novel screening platform for therapeutic development.

Co-Culture System of Human Enteroids/Colonoids with Innate Immune Cells

Human intestinal enteroids derived from adult stem cells offer a relevant ex vivo system to study biological processes of the human gut. They recreate cellular and functional features of the intestinal epithelium of the small intestine (enteroids) or colon (colonoids) albeit limited by the lack of associated cell types that help maintain tissue homeostasis and respond to external challenges. In the gut, innate immune cells interact with the epithelium, support barrier function, and deploy effector functions. We have established a co-culture system of enteroid/colonoid monolayers and underlying macrophages and polymorphonuclear neutrophils to recapitulate the cellular framework of the human intestinal epithelial niche. Enteroids are generated from biopsies or resected tissue from any segment of the human gut and maintained in long-term cultures as three-dimensional structures through supplementation of stem cell growth factors. Immune cells are isolated from fresh human whole blood or frozen peripheral blood mononuclear cells (PBMC). Monocytes from PBMC are differentiated into macrophages by cytokine stimulation prior to co-culture. The methods are divided into the two main components of the model: (1) generating enteroid/colonoid monolayers and isolating immune cells and (2) assembly of enteroid/colonoid-immune cell co-cultures with separate apical and basolateral compartments. Co-cultures containing macrophages can be maintained for 48 hr while those involving neutrophils, due to their shorter life span, remain viable for 4 hr. Enteroid-immune co-cultures enable multiple outcome measures, including transepithelial resistance, production of cytokines/chemokines, phenotypic analysis of immune cells, tissue immunofluorescence imaging, protein or mRNA expression, antigen or microbe uptake, and other cellular functions. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Seeding enteroid fragments onto Transwells for monolayer formation Alternate Protocol: Seeding enteroid fragments for monolayer formation using trituration Basic Protocol 2: Isolation of monocytes and derivation of immune cells from human peripheral blood Basic Protocol 3: Isolation of neutrophils from human peripheral blood Basic Protocol 4: Assembly of enteroid/macrophage or enteroid/neutrophil co-culture.

Evaluation of a Live Attenuated S. sonnei Vaccine Strain in the Human Enteroid Model

Shigella is a leading cause of bacillary dysentery worldwide, responsible for high death rates especially among children under five in low-middle income countries. Shigella sonnei prevails in high-income countries and is becoming prevalent in industrializing countries, where multi-drug resistant strains have emerged, as a significant public health concern. One strategy to combat drug resistance in S. sonnei is the development of effective vaccines. There is no licensed vaccine against Shigella, and development has been hindered by the lack of an effective small-animal model. In this work, we used human enteroids, for the first time, as a model system to evaluate a plasmid-stabilized S. sonnei live attenuated vaccine strain, CVD 1233-SP, and a multivalent derivative, CVD 1233-SP::CS2-CS3, which expresses antigens from enterotoxigenic Escherichia coli. The strains were also tested for immunogenicity and protective capacity in the guinea pig model, demonstrating their ability to elicit serum and mucosal antibody responses as well as protection against challenge with wild-type S. sonnei. These promising results highlight the utility of enteroids as an innovative preclinical model to evaluate Shigella vaccine candidates, constituting a significant advance for the development of preventative strategies against this important human pathogen.

Comparison of Antimicrobial Resistance, Virulence Genes, Phylogroups, and Biofilm Formation of Escherichia coli Isolated From Intensive Farming and Free-Range Sheep

Pathogenic E. coli are among the most frequently isolated bacterial pathogens on large-scale sheep farms in China. Antibiotic use in wool sheep production is a risk factor for promoting the emergence of resistant E. coli. To reveal the differences of E. coli populations in sheep from different farming systems the antimicrobial resistance, virulence genes, biofilm formation, and phylogroups of 500 E. coli isolates obtained between September 2019 and December 2020 in northwest China from diarrheic infections of intensive farming and free-range sheep were analyzed. The antimicrobial susceptibility test for 12 classes of antimicrobial agents was determined using the broth microdilution susceptibility method, and PCR was used to detect the differences in virulence genes and phylogroups. Additionally, biofilm formation was determined using microtiter plate and slide agglutination methods. Among the 500 E. coli isolates, the majority of the isolates were multidrug resistant (75.4%) and carried at least one virulence gene (94.8%). We observed that 412 (82.4%), 360 (72.0%), and 266 (53.2%) are found to be resistant to sulfisoxazole, florfenicol, and tetracyclines, respectively. Resistance was also observed to mequindox (46.8%), ampicillin (43.6%), spectinomycin (38.6%), enrofloxacin (34.2%), ceftiofur (21.0%), gentamycin (20.4%), ceftazidime (17.8%), and polymyxin B (7.8%) but no resistance was found to meropenem. These results showed that strains from free-range subjects had fewer antibiotic resistance strains rather than sheep that were intensively farmed (P < 0.05). We observed fifteen virulence genes, of which etrA (n = 401, 80.2%) is the most common. In addition, EAEC (86.4%) is dominant among free-range sheep and EHEC (80.1%) is dominant among intensive farming. Among all virulence genes, the strongest correlation was found between etrA and papC gene (P < 0.001, OR = 455.68). Similarly, the strongest correlation was also found between eltA and sulfisoxazole (P < 0.001, OR = 877). Furthermore, the majority of the E. coli isolates belonged to phylogroup B1 (50.6%), followed by phylogroup C (20.6%), A (7.4%), E (7.4%), D (5.8%), B2 (1.6%), and F (1%). Interestingly, phylogroup B2 and D were all distributed in intensive farms. In addition, 33 (6.6%), 373 (74.6%), and 94 (18.8%) showed moderate, weak, and no connection biofilm formation ability, respectively. These data uncovered that wool sheep serve as a reservoir of pathogenic E. coli harboring multiple resistance phenotypes and virulence genes. The overlapping virulence-associated traits between IPEC and ExPEC indicated the zoonotic potential and safety threats of sheep food products. It is urgent to improve the proper use of antimicrobials in China as well as other countries.

Antimicrobial Resistance in Escherichia coli Strains Isolated from Humans and Pet Animals

Throughout scientific literature, we can find evidence that antimicrobial resistance has become a big problem in the recent years on a global scale. Public healthcare systems all over the world are faced with a great challenge in this respect. Obviously, there are many bacteria that can cause infections in humans and animals alike, but somehow it seems that the greatest threat nowadays comes from the Enterobacteriaceae members, especially Escherichia coli. Namely, we are witnesses to the fact that the systems that these bacteria developed to fight off antibiotics are the strongest and most diverse in Enterobacteriaceae. Our great advantage is in understanding the systems that bacteria developed to fight off antibiotics, so these can help us understand the connection between these microorganisms and the occurrence of antibiotic-resistance both in humans and their pets. Furthermore, unfavorable conditions related to the ease of E. coli transmission via the fecal-oral route among humans, environmental sources, and animals only add to the problem. For all the above stated reasons, it is evident that the epidemiology of E. coli strains and resistance mechanisms they have developed over time are extremely significant topics and all scientific findings in this area will be of vital importance in the fight against infections caused by these bacteria.