The small intestine: dining table of host–microbiota meetings

Abstract

Growing evidence suggests the importance of the small intestinal bacteria in the diet-host-microbiota dialogue in various facets of health and disease. Yet, this body site is still poorly explored and its ecology and mechanisms of interaction with the host are just starting to be unraveled. In this review, we describe the current knowledge on the small intestinal ecology, its composition and diversity, and how the intestinal bacteria in homeostatic conditions participate in nutrient digestion and absorption. We illustrate the importance of a controlled bacterial density and of the preservation of absorptive surface for the host's nutritional status. In particular, we discuss these aspects of the small intestinal environment in the framework of two disease conditions, namely small intestinal bacterial overgrowth (SIBO) and short bowel syndrome (SBS). We also detail in vivo, ex vivo and in vitro models developed to simulate the small intestinal environment, some applied for (diet-)host-bacteria interaction studies. Lastly, we highlight recent technological, medical and scientific advances applicable to investigate this complex and yet understudied body environment to broaden our knowledge in support of further progress in the medical practice, and to proceed towards the integration of the (small)intestinal bacteria in personalized therapeutic approaches.

Dietary Hemin Remodels Gut Microbiota and Mediates Tissue Inflammation and Injury in the Small Intestine

“…To mimic the small intestinal condition accurately, the pH of MRS broth was adjusted to 6.5, which was regarded as consistent with the real situation in the small intestine. [ 34 ] We found that L. reuteri and L. paracasei showed significant differences in response to myoglobin and hemin, which was consistent with sequencing results. In addition, LEfSe analysis identified L. reuteri as the differential bacterium between the HMb and Hhe groups.…”

Periodontal Inflammation and Dysbiosis Relate to Microbial Changes in the Gut

“…Approximately ~1 L to 1.5 L of saliva containing ~10 11 oral bacterial cells daily reaches the intestinal tract. While many oral bacteria are destroyed, evidence showed that a significant number reach the gut [65], stimulate the immune system, and, with predisposing influences, can cause pathology [51]. The indirect mechanism implies that bacteria and inflammatory cytokines obtain access to the systemic circulation and then reach the gut or influence gut response.…”

Comparative Analysis of the Duodenojejunal Microbiome with the oral and fecal microbiome unveils its role in Human Severe Obesity

“…While these studies have provided valuable insights into the compositional and functional changes associated with obesity 1 , the FM represents only a fraction of the gastrointestinal tract (GIT) microbiome. Particularly, the upper small intestine (USI) is of great interest due to its crucial functions in food digestion, nutrient sensing, absorption, enterohormone production, and metabolic homeostasis 2,3 .…”

“…While studies in rodents demonstrated the causal influence of the USI microbiome (USIM) on metabolic regulation, clinical investigations concerning the USIM in human obesity, remain limited and contradictory 3 . There is a pressing need for further research to elucidate the intricate interplay between lifestyle, the USIM, and metabolic health in humans 2,3 .…”