Systematic review: gastric microbiota in health and disease

Abstract

Background Helicobacter pylori is the most infamous constituent of the gastric microbiota and its presence is the strongest risk factor for gastric cancer and other gastroduodenal diseases. Although historically the healthy stomach was considered a sterile organ, we now know it is colonised with a complex microbiota. However, its role in health and disease is not well understood. Aim To systematically explore the literature on the gastric microbiota in health and disease as well as the gut microbiota after bariatric surgery. Methods A systematic search of online bibliographic databases MEDLINE/EMBASE was performed between 1966 and February 2019 with screening in accordance with Preferred Reporting Items for Systematic Reviews and Meta‐Analyses guidelines. Randomised controlled trials, cohort studies and observational studies were included if they reported next‐generation sequencing derived microbiota analysis on gastric aspirate/tissue or stool samples (bariatric surgical outcomes). Results Sixty‐five papers were eligible for inclusion. With the exception of H pylori‐induced conditions, overarching gastric microbiota signatures of health or disease could not be determined. Gastric carcinogenesis induces a progressively altered microbiota with an enrichment of oral and intestinal taxa as well as significant changes in host gastric mucin expression. Proton pump inhibitors usage increases gastric microbiota richness. Bariatric surgery is associated with an increase in potentially pathogenic proteobacterial species in patient stool samples. Conclusion While H pylori remains the single most important risk factor for gastric disease, its capacity to shape the collective gastric microbiota remains to be fully elucidated. Further studies are needed to explore the intricate host/microbial and microbial/microbial interplay.

Mechanisms of the Epithelial–Mesenchymal Transition and Tumor Microenvironment in Helicobacter pylori-Induced Gastric Cancer

“…Helicobacter pylori (H. pylori) is a helix-shaped, Gram-negative, microaerophilic, flagellated bacterium that is capable of biofilm formation and converting from spiral to coccoid form [1][2][3][4][5][6]. It is a highly invasive microorganism responsible for one of the highest prevalences of chronic infections worldwide, even though over 80% of infected patients remain asymptomatic [7][8][9][10][11][12][13].…”

Helicobacter pylori infection and eradication: Exploring their impacts on the gastrointestinal microbiota

“…H pylori manipulates gastric milieu making this niche favorable for some microbial members while unfavorable for others with a global trend towards carcinogenesis. For example, commensal oral and intestinal bacteria are likely to benefit from these alterations as previous studies reported that gastric cancer microbiota was enriched with oral or intestinal taxa 8,10,11 . Interestingly, one study found apparent differences in the composition of microbiota between gastric aspirates and biopsies 6 .…”

“…Individuals with abundant H pylori in the stomach contain distinct intestinal communities compared with H pylori‐ negative counterparts, indicating an interplay between two gastrointestinal segments 10 . Although precise underlying mechanisms are still scarce, possible explanations are emerging.…”

“…Although the goal is to explore the impacts of H pylori infection on the intestinal flora, most recent studies performed sequencing analysis on fecal samples 31,33‐37,39 . Previous studies addressed that the profiles of fecal microbiota only partially recapitulated those of the mucosal microbiota 10,44 . Thus, future analyses based on intestinal biopsies are likely to provide more accurate information.…”

“…For example, researchers showed that the interactions among gastric microbes were greatly compromised in the presence of H pylori 8 . In the clinical scenario, H pylori‐ related dysbiosis has been linked to many digestive diseases 9‐11 . Thus, a better understanding of the dialogues between H pylori and other gastrointestinal microbial members might offer novel targets for prevention or treatment.…”