Enterohaemorrhagic Escherichia coli activates nitrate respiration to benefit from the inflammatory response for initiation of microcolony-formation

Gut microbiome-derived lipopolysaccharides aggravate cognitive impairment via TLR4-mediated inflammatory signaling in neonatal rats following hypoxic-ischemic brain damage

Hypoxic-ischemic brain damage (HIBD) is a leading cause of infant mortality and neurological disabilities in children. Recent evidence indicates that gut microbiota significantly contributes to the development of inflammation and cognitive impairments following brain injury. However, the mechanisms by which gut microbiota influence inflammation and cognitive function in the neonates after HIBD are not well understood. This study established a neonatal rat model of HIBD by the classic Rice-Vannucci technique to investigate gut dysbiosis following hypoxic-ischemic (HI) insult and to elucidate the causal relationship between gut dysbiosis and cognitive impairments. Our results demonstrated that HI insult resulted in significant gut microbial dysbiosis, characterized by an expansion of Enterobacteriaceae. This dysbiosis was associated with intestinal barrier damage, lipopolysaccharides (LPS) leakage, and systemic inflammation. Conversely, administration of aminoguanidine (AG) to inhibit Enterobacteriaceae overgrowth restored intestinal barrier integrity and reduced systemic inflammation. Importantly, AG treatment effectively suppressed microglial activation, neuronal damage, and cognitive impairments in the neonatal rats subjected to HI insult. Additionally, RNA sequencing analysis revealed that differentially expressed genes in both colonic and hippocampal tissues were primarily associated with inflammation and neuronal apoptosis after HI insult. Further mechanistic exploration revealed that AG treatment mitigated intestinal LPS leakage, thereby reducing the activation of the TLR4/MyD88/NF-κB signaling pathway and production of the downstream inflammatory cytokines in both the colon and hippocampus. Notably, fecal microbiota transplantation (FMT) from the HIBD rats to the antibiotic cocktail-treated recipient rats resulted in microglial activation, neuronal damage, and cognitive impairments in the recipients. However, these adverse effects were effectively mitigated in the recipient rats that received FMT from the AG-treated donors, as well as in those undergoing hippocampal TLR4 knockdown. In conclusion, our findings indicate that LPS derived from gut Enterobacteriaceae overgrowth plays a critical role in the TLR4-mediated inflammatory signaling, providing a novel microbiota-based therapeutic approach for cognitive impairments following neonatal HIBD.

Role of gastrointestinal microbial populations, a terra incognita of the human body in the management of intestinal bowel disease and metabolic disorders

Intestinal bowel disease (IBD) is a chronic immune-mediated clinical condition that affects the gastrointestinal tract and is mediated by an inflammatory response. Although it has been extensively studied, the multifactorial aetiology of this disorder makes it difficult to fully understand all the involved mechanisms in its development and therefore its treatment. In recent years, the fundamental role played by the human microbiota in the pathogenesis of IBD has been emphasised. Microbial imbalances in the gut bacterial communities and a lower species diversity in patients suffering from inflammatory gastrointestinal disorders compared to healthy individuals have been reported as principal factors in the development of IBD. These served to support scientific arguments for the use of probiotic microorganisms in alternative approaches for the prevention and treatment of IBD. In a homeostatic environment, the presence of bacteria (including probiotics) on the intestinal epithelial surface activates a cascade of processes by which immune responses inhibited and thereby commensal organisms maintained. At the same time these processes may support activities against specific pathogenic bacteria. In dysbiosis, these underlying mechanisms will serve to provoke a proinflammatory response, that, in combination with the use of antibiotics and the genetic predisposition of the host, will culminate in the development of IBD. In this review, we summarised the main causes of IBD, the physiological mechanisms involved and the related bacterial groups most frequently associated with these processes. The intention was to enable a better understanding of the interaction between the intestinal microbiota and the host, and to suggest possibilities by which this knowledge can be useful for the development of new therapeutic treatments.

Cause or effect? The spatial organization of pathogens and the gut microbiota in disease

The human gut hosts a dense and diverse microbial community, spatially organized in multiple scales of structure. Here, we review how microbial organization differs between health and disease. We describe how changes in spatial organization may induce alterations in gut homeostasis, concluding with a future outlook to reveal causality.