Indole-3-lactic acid associated with Bifidobacterium-dominated microbiota significantly decreases inflammation in intestinal epithelial cells

Background

Bifidobacterium longum subsp. infantis (B. infantis) is a commensal bacterium that colonizes the gastrointestinal tract of breast-fed infants. B. infantis can efficiently utilize the abundant supply of oligosaccharides found in human milk (HMO) to help establish residence. We hypothesized that metabolites from B. infantis grown on HMO produce a beneficial effect on the host.

Results

In a previous study, we demonstrated that B. infantis routinely dominated the fecal microbiota of a breast fed Bangladeshi infant cohort (1). Characterization of the fecal metabolome of binned samples representing high and low B. infantis populations from this cohort revealed higher amounts of the tryptophan metabolite indole-3-lactic acid (ILA) in feces with high levels of B. infantis. Further in vitro analysis confirmed that B. infantis produced significantly greater quantities of the ILA when grown on HMO versus lactose, suggesting a growth substrate relationship to ILA production. The direct effects of ILA were assessed in a macrophage cell line and intestinal epithelial cell lines. ILA (1-10 mM) significantly attenuated lipopolysaccharide (LPS)-induced activation of NF-kB in macrophages. ILA significantly attenuated TNF-α- and LPS-induced increase in the pro-inflammatory cytokine IL-8 in intestinal epithelial cells. ILA increased mRNA expression of the aryl hydrogen receptor (AhR)-target gene CYP1A1 and nuclear factor erythroid 2–related factor 2 (Nrf2)-targeted genes glutathione reductase 2 (GPX2), superoxide dismutase 2 (SOD2), and NAD(P) H dehydrogenase (NQO1). Pretreatment with either the AhR antagonist or Nrf-2 antagonist inhibited the response of ILA on downstream effectors.

Conclusions

These findings suggest that ILA, a predominant metabolite from B. infantis grown on HMO and elevated in infant stool high in B. infantis, and protects gut epithelial cells in culture via activation of the AhR and Nrf2 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02023-y.

Endocannabinoids Inhibit the Induction of Virulence in Enteric Pathogens

Endocannabinoids are host-derived lipid hormones that fundamentally impact gastrointestinal (GI) biology. The use of cannabis and other exocannabinoids as anecdotal treatments for various GI disorders inspired the search for mechanisms by which these compounds mediate their effects, which led to the discovery of the mammalian endocannabinoid system. Dysregulated endocannabinoid signaling was linked to inflammation and the gut microbiota. However, the effects of endocannabinoids on host susceptibility to infection has not been explored. Here, we show that mice with elevated levels of the endocannabinoid 2-arachidonoyl glycerol (2-AG) are protected from enteric infection by Enterobacteriaceae pathogens. 2-AG directly modulates pathogen function by inhibiting virulence programs essential for successful infection. Furthermore, 2-AG antagonizes the bacterial receptor QseC, a histidine kinase encoded within the core Enterobacteriaceae genome that promotes the activation of pathogen-associated type three secretion systems. Taken together, our findings establish that endocannabinoids are directly sensed by bacteria and can modulate bacterial function.

CRISPR/Cas9 Screens Reveal Requirements for Host Cell Sulfation and Fucosylation in Bacterial Type III Secretion System-Mediated Cytotoxicity

Type III secretion systems (T3SSs) inject bacterial effector proteins into host cells and underlie the virulence of many gram-negative pathogens. Studies have illuminated bacterial factors required for T3SS function, but the required host processes remain largely undefined. We coupled CRISPR/Cas9 genome editing technology with the cytotoxicity of two Vibrio parahaemolyticus T3SSs (T3SS1 and T3SS2) to identify human genome disruptions conferring resistance to T3SS-dependent cytotoxicity. We identity non-overlapping genes required for T3SS1- and T3SS2-mediated cytotoxicity. Genetic ablation of cell surface sulfation reduces bacterial adhesion and thereby alters the kinetics of T3SS1-mediated cytotoxicity. Cell surface fucosylation is required for T3SS2-dependent killing, and genetic inhibition of fucosylation prevents membrane insertion of the T3SS2 translocon complex. These findings reveal the importance of ubiquitous surface modifications for T3SS function, potentially explaining the broad tropism of V. parahaemolyticus, and highlight the utility of genome-wide CRISPR/Cas9 screens to discover processes underlying host-pathogen interactions.

Bifidobacteria grown on human milk oligosaccharides downregulate the expression of inflammation-related genes in Caco-2 cells

Background

Breastfed human infants are predominantly colonized by bifidobacteria that thrive on human milk oligosaccharides (HMO). Two predominant species of bifidobacteria in infant feces are Bifidobacterium breve (B. breve) and Bifidobacterium longum subsp. infantis (B. infantis), both of which include avid HMO-consumer strains. Our laboratory has previously shown that B. infantis, when grown on HMO, increases adhesion to intestinal cells and increases the expression of the anti-inflammatory cytokine interleukin-10. The purpose of the current study was to investigate the effects of carbon source—glucose, lactose, or HMO—on the ability of B. breve and B. infantis to adhere to and affect the transcription of intestinal epithelial cells on a genome-wide basis.

Results

HMO-grown B. infantis had higher percent binding to Caco-2 cell monolayers compared to B. infantis grown on glucose or lactose. B. breve had low adhesive ability regardless of carbon source. Despite differential binding ability, both HMO-grown strains significantly differentially affected the Caco-2 transcriptome compared to their glucose or lactose grown controls. HMO-grown B. breve and B. infantis both downregulated genes in Caco-2 cells associated with chemokine activity.

Conclusion

The choice of carbon source affects the interaction of bifidobacteria with intestinal epithelial cells. HMO-grown bifidobacteria reduce markers of inflammation, compared to glucose or lactose-grown bifidobacteria. In the future, the design of preventative or therapeutic probiotic supplements may need to include appropriately chosen prebiotics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0508-3) contains supplementary material, which is available to authorized users.

The impact of the milk glycobiome on the neonate gut microbiota

Human milk is a complete source of nourishment for the infant. Exclusive breastfeeding not only sustains the infant's development but also guides the proliferation of a protective intestinal microbiota. Among the many components of milk that modulate the infant gut microbiota, the milk glycans, which comprise free oligosaccharides, glycoproteins, and glycolipids, are increasingly recognized as drivers of microbiota development and overall gut health. These glycans may display pleiotropic functions, conferring protection against infectious diseases and also acting as prebiotics, selecting for the growth of beneficial intestinal bacteria. The prebiotic effect of milk glycans has direct application to prevention of diseases such as necrotizing enterocolitis, a common and devastating disease of preterm infants. In this article, we review the impact of the human (and bovine) milk glycome on gut health through establishment of a milk-oriented microbiota in the neonate.

Shiga toxin in enterohemorrhagic E.coli: regulation and novel anti-virulence strategies

Enterohemorrhagic Escherichia coli (EHEC) are responsible for major outbreaks of bloody diarrhea and hemolytic uremic syndrome (HUS) throughout the world. The mortality associated with EHEC infections stems from the production and release of a potent Shiga toxin (Stx) by these bacteria. Stx induces cell death in endothelial cells, primarily in the urinary tract, causing HUS. Stx was first described in Shigella dysenteriae serotype I by Kiyoshi Shiga and was discovered later in EHEC. Multiple environmental cues regulate the expression of Stx, including temperature, growth phase, antibiotics, reactive oxygen species (ROS), and quorum sensing. Currently, there is no effective treatment or prophylaxis for HUS. Because antibiotics trigger Stx production and their use to treat EHEC infections is controversial, alternative therapeutic strategies have become the focus of intense research. One such strategy explores quorum sensing inhibitors as therapeutics. These inhibitors target quorum sensing regulation of Stx expression without interfering with bacterial growth, leading to the hypothesis that these inhibitors impose less selective pressure for bacteria to develop drug resistance. In this review, we discuss factors that regulate Stx production in EHEC, as well as novel strategies to prevent and/or minimize the development of HUS in infected subjects.

Inter-kingdom signaling: chemical language between bacteria and host

Chemical communication between cells ensures coordination of behavior. In prokaryotes, this chemical communication is usually referred to as quorum sensing, while eukaryotic cells signal through hormones. In the past years, a growing number of reports have shown that bacterial quorum sensing signals, called autoinducers, signal to eukaryotic cells, mimicking hormones. Conversely, host hormones can signal to bacterial cells through converging pathways to autoinducer signaling. This inter-kingdom signaling mediates symbiotic and pathogenic relationships between bacteria, mammalian and plant hosts.

Involvement of the Helicobacter pylori plasticity region and cag pathogenicity island genes in the development of gastroduodenal diseases

Infection by Helicobacter pylori is associated with the development of several gastroduodenal diseases, including gastritis, peptic ulcer disease (gastric ulcers and duodenal ulcers), and gastric adenocarcinoma. Although a number of putative virulence factors have been reported for H. pylori, there are conflicting results regarding their association with specific H. pylori-related diseases. In this work, we investigated the presence of virB11 and cagT, located in the left half of the cag pathogenicity island (cagPAI), and the jhp917-jhp918 sequences, components of the dupA gene located in the plasticity zone of H. pylori, in Brazilian isolates of H. pylori. We also examined the association between these genes and H. pylori-related gastritis, peptic ulcer disease, and gastric and duodenal ulcers in an attempt to identify a gene marker for clinical outcomes related to infection by H. pylori. The cagT gene was associated with peptic ulcer disease and gastric ulcers, whereas the virB11 gene was detected in nearly all of the samples. The dupA gene was not associated with duodenal ulcers or any gastroduodenal disease here analyzed. These results suggest that cagT could be a useful prognostic marker for the development of peptic ulcer disease in the state of São Paulo, Brazil. They also indicate that cagT is associated with greater virulence and peptic ulceration, and that this gene is an essential component of the type IV secretion system of H. pylori.