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f Clostridium difficile is the leading cause of infectious nosocomial diarrhea. The pathogenesis of C. difficile infection (CDI) results from the interactions between the pathogen, intestinal epithelium, host immune system, and gastrointestinal microbiota. Previous studies of the host-pathogen interaction in CDI have utilized either simple cell monolayers or in vivo models. While much has been learned by utilizing these approaches, little is known about the direct interaction of the bacterium with a complex host epithelium. Here, we asked if human intestinal organoids (HIOs), which are derived from pluripotent stem cells and demonstrate small intestinal morphology and physiology, could be used to study the pathogenesis of the obligate anaerobe C. difficile. Vegetative C. difficile, microinjected into the lumen of HIOs, persisted in a viable state for up to 12 h. Upon colonization with C. difficile VPI 10463, the HIO epithelium is markedly disrupted, resulting in the loss of paracellular barrier function. Since similar effects were not observed when HIOs were colonized with the nontoxigenic C. difficile strain F200, we directly tested the role of toxin using TcdA and TcdB purified from VPI 10463. We show that the injection of TcdA replicates the disruption of the epithelial barrier function and structure observed in HIOs colonized with viable C. difficile. C lostridium difficile is an anaerobic, spore-forming bacterium that is the leading cause of infectious nosocomial diarrhea and is responsible for over 14,000 deaths annually (1). Human exposure to C. difficile results in a range of manifestations, from asymptomatic colonization, to diarrhea, to lethal toxic megacolon. Various models have been used to study C. difficile infection (CDI), including in vitro models using transformed cell lines and a variety of in vivo models (2-5). In vitro cell culture models are limited in their ability to recapitulate complexities of the human gastrointestinal tract, and detailed, real-time study of the mucosal epithelium during infection in an animal model is technically challenging.Human intestinal organoids (HIOs) are three-dimensional spheroids of human epithelium generated through directed differentiation of human pluripotent stem cells (hPSCs), which include human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). HIOs contain both mesenchymal and epithelial tissues that are structurally arranged around a central luminal cavity. The epithelial compartment of the HIO possesses an array of small intestinal cell types, including absorptive enterocytes and secretory Paneth, goblet, and enteroendocrine cells, in addition to Lgr5 ϩ intestinal stem cells (6). HIOs have been used to model features of embryonic development, viral infection, and inflammatory bowel disease (7-9). Due to their similarity to the human gastrointestinal tract, HIOs serve as a tractable and physiologically relevant model of the human intestine.We sought to use HIOs to study the interaction between C. difficile and complex human epit...

Infection by the bacterium Clostridium difficile causes an inflammatory diarrheal disease which can become life threatening and has grown to be the most prevalent nosocomial infection. Susceptibility to C. difficile infection is strongly associated with previous antibiotic treatment, which disrupts the gut microbiota and reduces its ability to prevent colonization. In this study, we demonstrated that C. difficile altered pathogenesis between hosts pretreated with antibiotics from separate classes and exploited different nutrient sources across these environments. Our metabolite score calculation also provides a platform to study nutrient requirements of pathogens during an infection. Our results suggest that C. difficile colonization resistance is mediated by multiple groups of bacteria competing for several subsets of nutrients and could explain why total reintroduction of competitors through fecal microbial transplant currently is the most effective treatment for recurrent CDI. This work could ultimately contribute to the identification of targeted, context-dependent measures that prevent or reduce C. difficile colonization, including pre- and probiotic therapies.

Clostridium difficile ( C. difficile ) incidence has tripled over the past 15 years and is attributed to the emergence of hypervirulent strains. While it is clear that C. difficile toxins cause damaging colonic inflammation, the immune mechanisms protecting from tissue damage require further investigation. Through a transcriptome analysis, we identify IL-33 as an immune target upregulated in response to hypervirulent C. difficile . We demonstrate that IL-33 prevents C. difficile -associated mortality and epithelial disruption independently of bacterial burden or toxin expression. IL-33 drives colonic group 2 innate lymphoid cell (ILC2) activation during infection and IL-33 activated ILC2s are sufficient to prevent disease. Furthermore, intestinal IL-33 expression is regulated by the microbiota as fecal microbiota transplantation (FMT) rescues antibiotic-associated depletion of IL-33. Lastly, dysregulated IL-33 signaling via the decoy receptor, sST2, predicts C. difficile -associated mortality in human patients. Thus, IL-33 signaling to ILC2s is an important mechanism of defense from C. difficile colitis.

Clostridium difficile has become the most common single cause of hospital-acquired infection over the last decade in the United States. Colonization resistance to the nosocomial pathogen is primarily provided by the gut microbiota, which is also involved in clearing the infection as the community recovers from perturbation. As distinct antibiotics are associated with different risk levels for CDI, we utilized a mouse model of infection with 3 separate antibiotic pretreatment regimens to generate alternative gut microbiomes that each allowed for C. difficile colonization but varied in clearance rate. To assess community-level dynamics, we implemented an integrative multi-omics approach that revealed that infection significantly changed many aspects of the gut community. The degree to which the community changed was inversely correlated with clearance during the first 6 days of infection, suggesting that C. difficile differentially modifies the gut environment to promote persistence. This is the first time that metagenome-enabled metatranscriptomics have been employed to study the behavior of a host-associated microbiota in response to an infection. Our results allow for a previously unseen understanding of the ecology associated with C. difficile infection and provide the groundwork for identification of context-specific probiotic therapies.

The involvement of host immunity in the gut microbiota-mediated colonization resistance to Clostridioides difficile infection (CDI) is incompletely understood. Here, we show that interleukin (IL)-22, induced by colonization of the gut microbiota, is crucial for the prevention of CDI in human microbiota-associated (HMA) mice. IL-22 signaling in HMA mice regulated host glycosylation, which enabled the growth of succinate-consuming bacteria Phascolarctobacterium spp. within the gut microbiome. Phascolarctobacterium reduced the availability of luminal succinate, a crucial metabolite for the growth of C. difficile , and therefore prevented the growth of C. difficile . IL-22-mediated host N -glycosylation is likely impaired in patients with ulcerative colitis (UC), and renders UC-HMA mice more susceptible to CDI. Transplantation of healthy human-derived microbiotas or Phascolarctobacterium reduced luminal succinate levels and restored colonization resistance in UC-HMA mice. IL-22-mediated host glycosylation thus fosters the growth of commensal bacteria that compete with C. difficile for the nutritional niche.

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Purpose Direct tests for Clostridium difficile are 30–50% more sensitive than tests for C. difficile toxins but the reasons for this discrepancy are incompletely understood. In addition to toxin degradation and strain differences, we hypothesized that C. difficile concentration could be important in determining whether toxins are detected in fecal samples. Methods We performed standard curves on an FDA-approved real-time PCR test for the C. difficile tcdB gene (Xpert C. difficile/Epi, Cepheid) during a prospective comparison of a toxin immunoassay (Meridian Premier), PCR and toxigenic culture. Immunoassay-negative, PCR-positive samples were retested with a cell cytotoxin assay (TechLab). Results Among 107 PCR-positive samples, 46 (43.0%) had toxins detected by immunoassay and an additional 18 (16.8%) had toxin detected by the cytotoxin assay yielding 64 (59.8%) toxin-positive and 43 (40.2%) toxin-negative samples. Overall, toxin-negative samples with C. difficile had 101–104 fewer DNA copies than toxin-positive samples and most discrepancies between toxin tests and PCR were associated with a significant difference in C. difficile quantity. 95% of toxin-positive samples had ≥4.1 log10 C. difficile tcdB DNA copies/mL. 52% of immunoassay-negative samples and 70% of immunoassay and cytotoxin negative samples had <4.1 log10 C. difficile tcdB DNA copies/mL. Conclusions These findings suggest that fecal C. difficile concentration is a major determinant of toxin detection and C. difficile quantitation may add to the diagnostic value of existing test methods. Future studies are needed to validate the utility of quantitation and determine the significance of low concentrations of C. difficile in the absence of detectable toxin.