Mucolytic bacteria license pathobionts to acquire host-derived nutrients during dietary nutrient restriction

Pathobionts employ unique metabolic adaptation mechanisms to maximize their growth in disease conditions. Adherent-invasive Escherichia coli (AIEC), a pathobiont enriched in the gut mucosa of patients with inflammatory bowel disease (IBD), utilizes diet-derived L-serine to adapt to the inflamed gut. Therefore, the restriction of dietary L-serine starves AIEC and limits its fitness advantage. Here, we find that AIEC can overcome this nutrient limitation by switching the nutrient source from the diet to the host cells in the presence of mucolytic bacteria. During diet-derived L-serine restriction, the mucolytic symbiont Akkermansia muciniphila promotes the encroachment of AIEC to the epithelial niche by degrading the mucus layer. In the epithelial niche, AIEC acquires L-serine from the colonic epithelium and thus proliferates. Our work suggests that the indirect metabolic network between pathobionts and commensal symbionts enables pathobionts to overcome nutritional restriction and thrive in the gut.

A potential pathogenic association between periodontal disease and Crohn's disease

Oral conditions are relatively common in patients with inflammatory bowel disease (IBD). However, the contribution of oral maladies to gut inflammation remains unexplored. Here, we investigated the effect of periodontitis on disease phenotypes of patients with IBD. In all, 60 patients with IBD (42 with ulcerative colitis [UC] and 18 with Crohn’s disease [CD]) and 45 healthy controls (HCs) without IBD were recruited for this clinical investigation. The effects of incipient periodontitis on the oral and gut microbiome as well as IBD characteristics were examined. In addition, patients were prospectively monitored for up to 12 months after enrollment. We found that, in both patients with UC and those with CD, the gut microbiome was significantly more similar to the oral microbiome than in HCs, suggesting that ectopic gut colonization by oral bacteria is increased in patients with IBD. Incipient periodontitis did not further enhance gut colonization by oral bacteria. The presence of incipient periodontitis did not significantly affect the clinical outcomes of patients with UC and CD. However, the short CD activity index increased in patients with CD with incipient periodontitis but declined or was unchanged during the study period in patients without periodontitis. Thus, early periodontitis may associate with worse clinically symptoms in some patients with CD.

The Intermucosal Connection between the Mouth and Gut in Commensal Pathobiont-Driven Colitis

The precise mechanism by which oral infection contributes to the pathogenesis of extra-oral diseases remains unclear. Here, we report that periodontal inflammation exacerbates gut inflammation in vivo. Periodontitis leads to expansion of oral pathobionts, including Klebsiella and Enterobacter species, in the oral cavity. Amassed oral pathobionts are ingested and translocate to the gut, where they activate the inflammasome in colonic mononuclear phagocytes, triggering inflammation. In parallel, periodontitis results in generation of oral pathobiont-reactive Th17 cells in the oral cavity. Oral pathobiont-reactive Th17 cells are imprinted with gut tropism and migrate to the inflamed gut. When in the gut, Th17 cells of oral origin can be activated by translocated oral pathobionts and cause development of colitis, but they are not activated by gut-resident microbes. Thus, oral inflammation, such as periodontitis, exacerbates gut inflammation by supplying the gut with both colitogenic pathobionts and pathogenic T cells.

Interleukin-22-mediated host glycosylation prevents Clostridioides difficile infection by modulating the metabolic activity of the gut microbiota

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 microbiota 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.

Hyaluronic acid-bilirubin nanomedicine for targeted modulation of dysregulated intestinal barrier, microbiome and immune responses in colitis

While conventional approaches for inflammatory bowel diseases mainly focus on suppressing hyperactive immune responses, it remains unclear how to address disrupted intestinal barriers, dysbiosis of the gut commensal microbiota and dysregulated mucosal immune responses in inflammatory bowel diseases. Moreover, immunosuppressive agents can cause off-target systemic side effects and complications. Here, we report the development of hyaluronic acid-bilirubin nanomedicine (HABN) that accumulates in inflamed colonic epithelium and restores the epithelium barriers in a murine model of acute colitis. Surprisingly, HABN also modulates the gut microbiota, increasing the overall richness and diversity and markedly augmenting the abundance of Akkermansia muciniphila and Clostridium XIVα, which are microorganisms with crucial roles in gut homeostasis. Importantly, HABN associated with pro-inflammatory macrophages, regulated innate immune responses and exerted potent therapeutic efficacy against colitis. Our work sheds light on the impact of nanotherapeutics on gut homeostasis, microbiome and innate immune responses for the treatment of inflammatory diseases.

Neonatal acquisition of Clostridia species protects against colonization by bacterial pathogens

The high susceptibility of neonates to infections has been assumed to be due to immaturity of the immune system, but the mechanism remains unclear. By colonizing adult germ-free mice with the cecal contents of neonatal and adult mice, we show that the neonatal microbiota is unable to prevent colonization by two bacterial pathogens that cause mortality in neonates. The lack of colonization resistance occurred when Clostridiales were absent in the neonatal microbiota. Administration of Clostridiales, but not Bacteroidales, protected neonatal mice from pathogen infection and abrogated intestinal pathology upon pathogen challenge. Depletion of Clostridiales also abolished colonization resistance in adult mice. The neonatal bacteria enhanced the ability of protective Clostridiales to colonize the gut.

Weight gain in mice on a high caloric diet and chronically treated with omeprazole depends on sex and genetic background

The impact of omeprazole (OM), a widely used over-the-counter proton pump inhibitor, on weight gain has not been extensively explored. We examined what factors, e.g., diet composition, microbiota, genetic strain, and sex, might affect weight gain in mice fed a high caloric diet while on OM. Inbred C57BL/6J strain, a 50:50 hybrid (B6SJLF1/J) strain, and mice on a highly mixed genetic background were fed four diets: standard chow (STD, 6% fat), STD with 200 ppm OM (STD + O), a high-energy chow (HiE, 11% fat), and HiE chow with OM (HiE + O) for 17 wk. Metabolic analysis, body composition, and fecal microbiota composition were analyzed in C57BL/6J mice. Oral glucose tolerance tests were performed using mice on the mixed background. After 8 wk, female and male C57BL/6J mice on the HiE diets ate less, whereas males on the HiE diets compared with the STD diets gained weight. All diet treatments reduced energy expenditure in females but in males only those on the HiE + O diet. Gut microbiota composition differed in the C57BL/6J females but not the males. Hybrid B6SJLF1/J mice showed similar weight gain on all test diets. In contrast, mixed strain male mice fed a HiE + O diet gained ∼40% more weight than females on the same diet. In addition to increased weight gain, mixed genetic mice on the HiE + O diet cleared glucose normally but secreted more insulin. We concluded that sex and genetic background define weight gain and metabolic responses of mice on high caloric diets and OM.

Functional Characterization of Inflammatory Bowel Disease-Associated Gut Dysbiosis in Gnotobiotic Mice

BACKGROUND & AIMS

Gut dysbiosis is closely involved in the pathogenesis of inflammatory bowel disease (IBD). However, it remains unclear whether IBD-associated gut dysbiosis contributes to disease pathogenesis or is merely secondary to intestinal inflammation. We established a humanized gnotobiotic (hGB) mouse system to assess the functional role of gut dysbiosis associated with 2 types of IBD: Crohn's disease (CD) and ulcerative colitis (UC).

METHODS

Germ-free mice were colonized by the gut microbiota isolated from patients with CD and UC, and healthy controls. Microbiome analysis, bacterial functional gene analysis, luminal metabolome analysis, and host gene expression analysis were performed in hGB mice. Moreover, the colitogenic capacity of IBD-associated microbiota was evaluated by colonizing germ-free colitis-prone interleukin 10-deficient mice with dysbiotic patients' microbiota.

RESULTS

Although the microbial composition seen in donor patients' microbiota was not completely reproduced in hGB mice, some dysbiotic features of the CD and UC microbiota (eg, decreased diversity, alteration of bacterial metabolic functions) were recapitulated in hGB mice, suggesting that microbial community alterations, characteristic for IBD, can be reproduced in hGB mice. In addition, colonization by the IBD-associated microbiota induced a proinflammatory gene expression profile in the gut that resembles the immunologic signatures found in CD patients. Furthermore, CD microbiota triggered more severe colitis than healthy control microbiota when colonized in germ-free interleukin 10-deficient mice.

CONCLUSIONS

Dysbiosis potentially contributes to the pathogenesis of IBD by augmenting host proinflammatory immune responses. Transcript profiling: GSE73882.

Rifaximin, gut microbes and mucosal inflammation: unraveling a complex relationship

Rifaximin is a non-systemic, broad-spectrum antibiotic that acts against gram-positive, gram-negative, and anaerobic bacteria. Clinical studies indicate that rifaximin is beneficial in treating irritable bowel syndrome (IBS). The mechanism responsible for the beneficial effects of rifaximin is not clear. In a recent study, we reported that rifaximin alters the bacterial population in the ileum of rats, leading to a relative abundance of Lactobacillus species. These changes prevent gut inflammation and visceral hyperalgesia caused by chronic stress. To more closely mirror human clinical studies in which rifaximin is used to treat IBS symptoms, we performed additional studies and showed that rifaximin reversed mucosal inflammation and barrier dysfunction evoked by chronic stress. These beneficial effects were accompanied by a striking increase in the abundance of Lactobacillaceae and a marked reduction in the number of segmented filamentous bacteria after rifaximin treatment. These microbial changes may contribute to the antiinflammatory effects of rifaximin on the intestinal mucosa.

Total parenteral nutrition-associated lamina propria inflammation in mice is mediated by a MyD88-dependent mechanism

Enteral nutrient deprivation via total parenteral nutrition (TPN) administration leads to local mucosal inflammatory responses, but the underlying mechanisms are unknown. Wild-type (WT) and MyD88(-/-) mice underwent jugular vein cannulation. One group received TPN without chow, and controls received standard chow. After 7 d, we harvested intestinal mucosally associated bacteria and isolated small-bowel lamina propria (LP) cells. Bacterial populations were analyzed using 454 pyrosequencing. LP cells were analyzed using quantitative PCR and multicolor flow cytometry. WT, control mucosally associated microbiota were Firmicutes-dominant, whereas WT TPN mice were Proteobacteria-domiant. Similar changes were observed in MyD88(-/-) mice with TPN administration. UniFrac analysis showed divergent small bowel and colonic bacterial communities in controls, merging toward similar microbiota (but distinct from controls) with TPN. The percentage of LP T regulatory cells significantly decreased with TPN in WT mice. F4/80(+)CD11b(+)CD11c(dull/-) macrophage-derived proinflammatory cytokines significantly increased with TPN. These proinflammatory immunologic changes were significantly abrogated in MyD88(-/-) TPN mice. Thus, TPN administration is associated with significant expansion of Proteobacteria within the intestinal microbiota and increased proinflammatory LP cytokines. Additionally, MyD88 signaling blockade abrogated decline in epithelial cell proliferation and epithelial barrier function loss.

Occurrence of Acanthocephalans in Largemouth Bass and Smallmouth Bass (Centrarchidae) From Gull Lake, Michigan

A total of 65 largemouth bass, Micropterus salmoides, and 27 smallmouth bass, M. dolomieu, collected in April-September 2000 and April-July 2001 from Gull Lake, Michigan, were examined for acanthocephalans. Leptorhynchoides thecatus and Neoechinorhynchus cylindratus infected all the bass examined. Leptorhynchoides thecatus had the highest mean intensity (258.2 +/- 185.4 in 2000 and 145.0 +/- 61.0 in 2001) of the species infecting smallmouth bass. Although N. cylindratus had higher mean intensities (42.1 +/- 37.9 in 2000 and 68.9 +/- 70.5 in 2001) than did L. thecatus in largemouth bass, the values were not significantly different between bass species. The prevalence, mean intensity, and mean abundance of Pomphorhynchus bulbocolli in the bass species were below the values for the other acanthocephalan species. Leptorhynchoides thecatus and N. cylindratus are the most abundant intestinal helminths in bass from Gull Lake.

Helminth communities of green frogs Rana clamitans Latreille, from southwestern Michigan

A total of 239 green frogs Rana clamitans, collected between June 3 and August 27, 1998 from 6 locations in southwestern Michigan, was examined for helminths. Of the 26 helminth taxa found, the larval cestode Mesocestoides sp. had the highest mean intensity, followed by the larval trematode Fibricola sp. Of the helminths that mature in frogs, Haematoloechus varioplexus had the highest prevalence and Gorgodera amplicava had the highest mean intensity. Frogs from 118th Pond had the highest species richness (20), mean helminth species richness (5.2), and mean helminth abundance (153.7). Frogs from Constantine East had the highest mean helminth species diversity (0.8778) and evenness (0.6033), followed by frogs from 118th Pond. In all comparisons of mean helminth community species richness, abundance, diversity, and evenness, adult frogs had significantly higher or higher values than did juveniles at each location. Jaccard's coefficients of similarity for the helminth communities for location pairs ranged from 0.545 to 0.823. Nine and 2 core helminth taxa occurred at the local and regional levels, respectively. The differences in several helminth community measures in green frogs among locations stress the importance of local ecological conditions on helminth community structure.

Organochlorine insecticides, polychlorinated biphenyls, and metals in water, sediment, and green frogs from southwestern Michigan

In an attempt to explain the etiology of frog deformities and population declines, many possible causative factors have been examined, including the input of synthetic chemicals into aquatic systems, where frogs spend much of their lives, including their entire developmental stages. Deformities in populations of green frogs in wetlands of southwestern Michigan that are influenced by agricultural, urban, or industrial inputs were assessed in this study. Of the 1445 green frogs (Rana clamitans) examined, only four (0.3%) exhibited morphological deformities. This deformity rate is less than the recognized background level of deformities for this species, which is approximately 1%. Concentrations of organochlorine insecticides, polychlorinated biphenyls (PCBs), and metals were determined in water, sediment, frog eggs, tadpoles, and adult green frog tissues. Concentrations of all individual organochlorine insecticides in tissue were less than 6 ng/g, wet wt. Concentrations of sigmaPCBs in tissue did not exceed 100 ng/g, wet wt. Concentrations of toxic metals were less than the limits of detection. Because no significant numbers of green frog deformities were observed in this region, it can be assumed that at these low concentrations, physical malformations in green frogs should not be observed. Significance of study. This study provides information on the incidence of deformities in green frog populations in southwestern Michigan and offers background data on chemical residues in green frogs and their environment.