Mastitis is one of the most prevalent diseases in dairy farming worldwide. The gut microbiota plays an important role in the regulation of systemic and local inflammatory diseases, such as mastitis. However, the regulatory mechanism of the gut microbiota on mastitis is still unclear. Thus, the aim of this study was to investigate the function and regulatory mechanisms of the gut microbiota in host defense against mastitis caused by Staphylococcus aureus (S. aureus) infection. Increased blood-milk barrier permeability, and S. aureus-induced mastitis severity were observed gut microbiota-dysbiosis mice compared with those in control mice. Moreover, feces microbiota transplantation (FMT) to microbbiota-dysbiosis mice reversed these effects. Furthermore, established disruption of commensal homeostasis results in significantly increased abundance of pathogenic Enterobacter bacteria, while the relative abundance of short-chain fatty acid (SCFAs)-producing bacterial phyla (Firmicutes and Bacteroidetes) was significantly reduced. However, FMT to gut microbiota-dysbiosis mice reversed these changes. In addition, dysbiosis reduced the levels of SCFAs, and administration of sodium propionate, sodium butyrate, and probiotics (butyrate-producing bacteria) reversed the changes in the blood-milk barrier and reduced the severity of mastitis induced by S. aureus. In conclusion, this new finding demonstrated that the gut microbiota acts as a protective factor in host defense against mastitis and that targeting the gut-mammary gland axis represents a promising therapeutic approach for mastitis treatment.

The precise mechanism by which gut dysbiosis contributes to the pathogenesis of extraintestinal diseases and how commensal microbes mediate these processes remain unclear. Here, we show that cows with mastitis had marked gut dysbiosis, characterized by the enrichment of opportunistic pathogenic Escherichia_Shigella and the depletion of commensal Roseburia. Fecal microbiota transplantation from donor cows with mastitis (M-FMT) to recipient mice significantly caused mastitis and changed the gut and mammary microbiota in mice. Notably, M-FMT facilitated the translocation of pathobiont from the gut into the mammary gland, and the depletion of Enterobacteriaceae alleviated M-FMT-induced mastitis in mice. In contrast, commensal Roseburia intestinalis improved M-FMT-induced mastitis and microbial dysbiosis in the gut and mammary gland and limited bacterial translocation by producing butyrate, which was associated with inflammatory signaling inhibition and barrier repair. Our research suggests that commensal Roseburia alleviates gut-dysbiosis-induced mastitis, although further studies in dairy cows and humans are needed.

Although emerging evidence shows that gut microbiota-mediated metabolic changes regulate intestinal pathogen invasions, little is known about whether and how gut microbiota-mediated metabolites affect pathogen infection in the distal organs. In this study, untargeted metabolomics was performed to identify the metabolic changes in a subacute ruminal acidosis (SARA)-associated mastitis model, a mastitis model with increased susceptibility toStaphylococcus aureus(S. aureus). The results showed that cows with SARA had reduced cholic acid (CA) and deoxycholic acid (DCA) levels compared to healthy cows. Treatment of mice with DCA, but not CA, alleviatedS. aureus-induced mastitis by improving inflammation and the blood-milk barrier integrity in mice. DCA inhibited the activation of NF-κB and NLRP3 signatures caused byS. aureusin the mouse mammary epithelial cells, which was involved in the activation of TGR5. DCA-mediated TGR5 activation inhibited the NF-κB and NLRP3 pathways and mastitis caused byS. aureusvia activating cAMP and PKA. Moreover, gut-dysbiotic mice had impaired TGR5 activation and aggravatedS. aureus-induced mastitis, while restoring TGR5 activation by spore-forming bacteria reversed these changes. Furthermore, supplementation of mice with secondary bile acids producerClostridium scindensalso activated TGR5 and alleviatedS. aureus-induced mastitis in mice. These results suggest that impaired secondary bile acid production by gut dysbiosis facilitates the development ofS. aureus-induced mastitis and highlight a potential strategy for the intervention of distal infection by regulating gut microbial metabolism.

The intestinal microbiota has been associated with the occurrence and development of mastitis, which is one of the most serious diseases of lactating women and female animals, but the underlying mechanism has not yet been elucidated. Aryl hydrocarbon receptor (AhR) activation by microbiota tryptophan metabolism-derived ligands is involved in maintaining host homeostasis and resisting diseases. We investigated whether AhR activation by microbiota-metabolic ligands could influence mastitis development in mice. In this study, we found that AhR activation using Ficz ameliorated mastitis symptoms, which were related to limiting NF-κB activation and enhancing barrier function. Impaired AhR activation by disturbing the intestinal microbiota initiated mastitis, and processed Escherichia coli (E. coli)-induced mastitis in mice. Supplementation with dietary tryptophan attenuated the mastitis, but attenuation was inhibited by the intestinal microbiota abrogation, while administering tryptophan metabolites including IAld and indole but not IPA, rescued the tryptophan effects in dysbiotic mice. Supplementation with a Lactobacillus reuteri (L. reuteri) strain with the capacity to produce AhR ligands also improved E. coli-induced mastitis in an AhR-dependent manner. These findings provide evidence for novel therapeutic strategies for treating mastitis, and support the role of metabolites derived from the intestinal microbiota in improving distal disease.

Alpinetin, a composition of Alpinia katsumadai Hayata, has been reported to have a number of biological properties, such as antibacterial, antitumor and other important therapeutic activities. However, the effect of alpinetin on inflammatory bowel disease (IBD) has not yet been reported. The purpose of this study was to investigate the anti-inflammatory effect and mechanism of alpinetin on dextran sulfate sodium (DSS)-induced colitis in mice. In vivo, DSS-induced mice colitis model was established by giving mice drinking water containing 5% (w/v) DSS for 7 days. Alpinetin (25, 50 and 100 mg/kg) were administered once a day by intraperitoneal injection 3 days before DSS treatment. In vitro, phorbol myristate acetate (PMA)-differentiated monocytic THP-1 macrophages were treated with alpinetin and stimulated by lipopolysaccharide (LPS). The results showed that alpinetin significantly attenuated diarrhea, colonic shortening, histological injury, myeloperoxidase (MPO) activity and the expressions of tumor necrosis factor (TNF-α) and interleukin (IL-1β) production in mice. In vitro, alpinetin markedly inhibited LPS-induced TNF-α and IL-1β production, as well as Toll-like receptor 4 (TLR4) mediated nuclear transcription factor-kappaB (NF-κB) and NOD-like receptor protein 3 (NLRP3) inflammasome activation. In conclusion, this study demonstrated that alpinetin had protective effects on DSS-induced colitis and may be a promising therapeutic reagent for colitis treatment.