Although the colonic cell line Caco-2 is widely used as a model of the small intestinal barrier function, it has limitations such as overestimated transepithelial electrical resistance (TEER) compared to in vivo conditions. Therefore, we investigated Human Intestinal Epithelial Cells (HIECs) as an alternative in vitro model.

Probiotic–host interaction can be cell-to-cell or through metabolite production. Dead (inactive) organisms could interact with the host, leading to local effects and possible health benefits. This research examined the effects of live and heat-inactivated Bifidobacterium animalis subsp. lactis, BB-12 (BB-12) and Lactobacillus rhamnosus GG (LGG) on cultured Caco-2 cells focusing on epithelial integrity and production of inflammatory mediators. Live organisms increased transepithelial electrical resistance (TEER), a barrier-integrity marker, with LGG having a greater effect than BB-12. When mildly heat-treated, both organisms had a more modest effect on TEER than when alive. When they were heat-inactivated, both organisms had only a limited effect on TEER. Neither live nor heat-inactivated organisms affected production of six inflammatory mediators produced by Caco-2 cells compared to control conditions. Pre-treatment with heat-inactivated LGG or BB-12 did not alter the decline in TEER caused by exposure to an inflammatory cocktail of cytokines. However, pre-treatment of Caco-2 cells with heat-inactivated organisms alone or their combination decreased the production of interleukin (IL)-6, IL-18, and vascular endothelial growth factor. To conclude, while the live organisms improve the epithelial barrier using this model, neither live nor heat-inactivated organisms directly elicit an inflammatory response by the epithelium. Pre-treatment with heat-inactivated BB-12 or LGG can reduce some components of the response induced by an inflammatory stimulus.

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial metabolic disorder that poses health challenges worldwide and is expected to continue to rise dramatically. NAFLD is associated with metabolic syndrome, type 2 diabetes mellitus, and impaired gut health. Increased gut permeability, caused by disturbance of tight junction proteins, allows passage of damaging microbial components that, upon reaching the liver, have been proposed to trigger the release of inflammatory cytokines and generate cellular stress. A growing body of research has suggested the utilization of targeted probiotic supplements as a preventive therapy to improve gut barrier function and tight junctions. Furthermore, specific microbial interactions and metabolites induce the secretion of hormones such as GLP-1, resulting in beneficial effects on liver health. To increase the likelihood of finding beneficial probiotic strains, we set up a novel screening platform consisting of multiple in vitro and ex vivo assays for the screening of 42 bacterial strains. Analysis of transepithelial electrical resistance response via co-incubation of the 42 bacterial strains with human colonic cells (Caco-2) revealed improved barrier integrity. Then, strain-individual metabolome profiling was performed revealing species-specific clusters. GLP-1 secretion assay with intestinal secretin tumor cell line (STC-1) found at least seven of the strains tested capable of enhancing GLP-1 secretion in vitro. Gene expression profiling in human biopsy-derived intestinal organoids was performed using next generation sequencing transcriptomics post bacterial co-incubation. Here, different degrees of immunomodulation by the increase in certain cytokine and chemokine transcripts were found. Treatment of mouse primary hepatocytes with selected highly produced bacterial metabolites revealed that indole metabolites robustly inhibited de novo lipogenesis. Collectively, through our comprehensive bacterial screening pipeline, not previously ascribed strains from both Lactobacillus and Bifidobacterium genera were proposed as potential probiotics based on their ability to increase epithelial barrier integrity and immunity, promote GLP-1 secretion, and produce metabolites relevant to liver health.

Probiotics have a longstanding association with human health, yet the mechanisms behind their benefits are often unclear. To understand the mode of action for the efficacy of a probiotic, it is important to take a broad overview of the interactions between the microbe, its environment, and the host. The BB-12 Bifidobacterium animalis subsp. lactis strain is one of the most documented probiotic strains on the market and has been shown to be effective in alleviating symptoms of a low defecation frequency and infant colic, among others. In this review, we examine the wide range of preclinical and clinical data available for the strain, to help elucidate some of its potential mechanisms of action. We describe the defence mechanisms developed by the strain to ensure gastrointestinal survival and transit, as well as the current knowledge on how BB-12 interacts with the host epithelial lining and cells of the immune system and the relationship between the strain and the gut microbiota. Collectively, the well documented clinical efficacies demonstrated by BB-12 are most likely not through one single mechanism, but through the collective direct and indirect effects the strain has on both its environment and the host.

Metabolic exchanges between strains in gut microbial communities shape their composition and interactions with the host. This study investigates the metabolic synergy between potential probiotic bacteria and Saccharomyces boulardii, aiming to enhance anti-inflammatory effects within a multi-species probiotic community. By screening a collection of 85 potential probiotic bacterial strains, we identified two strains that demonstrated a synergistic relationship with S. boulardii in pairwise co-cultivation. Furthermore, we computationally predicted cooperative communities with symbiotic relationships between S. boulardii and these bacteria. Experimental validation of 28 communities highlighted the role of S. boulardii as a key player in microbial communities, significantly boosting the community’s cell number and production of anti-inflammatory effectors, thereby affirming its essential role in improving symbiotic dynamics. Based on our observation, one defined community significantly activated the aryl hydrocarbon receptor—a key regulator of immune response—280-fold more effectively than the community without S. boulardii. This study underscores the potential of microbial communities for the design of more effective probiotic formulations.

Human milk provides essential nutrients for infants but also consists of human milk oligosaccharides (HMOs), which are resistant to digestion by the infant. Bifidobacteria are among the first colonizers, providing various health benefits for the host. This is largely facilitated by their ability to efficiently metabolize HMOs in a species-specific way. Nevertheless, these abilities can vary significantly by strain, and our understanding of the mechanisms applied by different strains from the same species remains incomplete. Therefore, we assessed the effects of strain-level genomic variation in HMO utilization genes on growth on HMOs in 130 strains from 10 species of human associated bifidobacteria. Our findings highlight the extent of genetic diversity between strains of the same species and demonstrate the effects on species-specific HMO utilization, which in most species is largely retained through the conservation of a core set of genes or the presence of redundant pathways. These data will help to refine our understanding of the genetic factors that contribute to the persistence of individual strains and will provide a better mechanistic rationale for the development and optimization of new early-life microbiota-modulating products to improve infant health.