Bacteria in the stomach

Association between gut microbiota and peptic ulcer disease, particularly gastric ulcer and duodenal ulcer: a two-sample Mendelian randomization study

Background

Recent an observational study has suggested a potential connection between gut microbiota (GM) and peptic ulcer diseases (PUDs), particularly gastric ulcer (GU) and duodenal ulcer (DU). However, the causal connection remains unsure.

Methods

A two-sample Mendelian randomization (MR) is carried out to explore the connection between the GM and DU or GU. Data on the GM comes from the MiBioGend database, and GU or DU data are based on the FinnGen database. One group of single nucleotide polymorphisms (SNPs) (P < 5 × 10-8) are served as instrumental variables (IVs). To obtain a more comprehensive conclusion, the other SNPs (P < 1 × 10-5) are selected as IVs. Inverse variance weighting (IVW) is used to determine the causal relationship.

Results

At the level of P < 1 × 10-5, the IVW analysis suggests that Clostridiaceae1, Butyriccoccus, and Peptcoccus have harmful effects on GU, while LachnospiraceaeUCG004 and MollicutesRF9 have beneficial effects on GU. Then, in the case of DU, the IVW analysis suggested that Lentisphaeria, Negativicutes, Clostridiaceae1, ClostridiumseMnsustricto1, ErysipelotrichaceaeUCG003, LachnospiraceaeNC2004group, Selenomonadale, Victivallales, and Lentisphaerae have harmful effects, while Catenibacterium, Escherichia.Shigella, LachnospiraceaeUCG008, and Sutterella have beneficial effects. When P < 5 × 10-8, IVW analysis suggests that GM has no significant influence on GU or DU.

Conclusion

This two-sample MR indicates a causal relationship between GM and GU or DU.

Comparisons Between Bacterial Communities in Mucosa in Patients With Gastric Antrum Ulcer and a Duodenal Ulcer

Objective: To identify and compare the bacterial community profile of mucosal tissues from a gastric antrum ulcer and a duodenal ulcer in Helicobacter pylori (Hp) positive dyspeptic patients. Methods: Genomic DNA was extracted from the mucosal tissues obtained from 18 patients diagnosed with gastric antrum or duodenal ulcers. A library was constructed using 16S rRNA gene amplification, and Miseq high-throughput sequencing was used to analyse the amplified products. Bioinformatics methods, including operational taxonomic units (OTUs), hierarchical clustering, and a diversity analysis, were performed to investigate and characterize the community composition. Results: The proportion of Helicobacter in the mucosa of patients with a gastric antrum ulcer was significantly higher than that of patients with a duodenal ulcer. However, the diversity of the bacterial community in the gastric antrum ulcer mucosa was significantly lower compared with the mucosa of the duodenal ulcer. There were significant differences in microbial community structure between the gastric antrum ulcer and the duodenal ulcer. Notably, Helicobacter, Prevotella, Neisseria, and Streptococcus were also predominant genera in the bacterial community of the duodenal ulcer mucosa, and they outnumbered those species in gastric antrum ulcer mucosa. Conclusion: The bacterial community composition and the corresponding abundance differ between the mucosal tissues of Hp positive gastric antrum ulcer and duodenal ulcer patients. Additionally, the bacterial community diversity in the mucosal tissues from gastric duodenal ulcer patients is higher than that from gastric antrum ulcer patients, and Helicobacter is not the absolutely predominant genus.

Effect of Helicobacter pylori Infection on the Composition of Gastric Microbiota in the Development of Gastric Cancer

BACKGROUND

Gastric cancer is one of the most common cancer types worldwide. In China, gastric cancer has become one of the major threats for public health, ranking second on incidence and third on cause of cancer death. Despite the common risk factors that promote the development of gastric cancer, the huge quantity of microorganism colonies within the gastrointestinal tract, particularly Helicobacter pylori infection, demonstrates a correlation with chronic inflammation and gastric carcinogenesis, as epidemiological studies have determined that H. pylori infection confers approximately 75% of the attributable risk for gastric cancer.

SUMMARY

The current article draws an overview on the correlation between the microbiota, inflammation and gastric tumorigenesis. H. pylori infection has been identified as the main risk factor as it triggers epithelial barrier disruption, survival signaling as well as genetic/epigenetic modulation. Apart from H. pylori, the existence of a diverse and complex composition of microbiota in the stomach has been identified, which supports a role of microbiota in the development of gastric cancer. Moreover, metagenomics studies focused on the composition and function of the microbiota have associated microbiota with gastric metabolic diseases and even tumorigenesis. Apart from the gastric microbiota, inflammation is another identified contributor to cancer development as well.

KEY MESSAGE

Though H. pylori infection and the non-H. pylori microbiota play a role in gastric cancer, the properties of gastric microbiota and mechanisms by which they participate in the genesis of gastric cancer are still not clearly depicted. Moreover, it remains to be understood how the presence of microbiota along with H. pylori infection affects the progress from gastric disease to cancer.

PRACTICAL IMPLICATIONS

This article summarized a clue of the current studies on microbiota, H. pylori infection and the progression from gastric disease to cancer.

Upper gastrointestinal microbiota and digestive diseases

Metagenomics which combines the power of genomics, bioinformatics, and systems biology, provide new access to the microbial world. Metagenomics permit the genetic analysis of complex microbial populations without requiring prior cultivation. Through the conceptual innovations in metagenomics and the improvements in DNA high-throughput sequencing and bioinformatics analysis technology, gastrointestinal microbiology has entered the metagenomics era and become a hot topic worldwide. Human microbiome research is underway, however, most studies in this area have focused on the composition and function of the intestinal microbiota and the relationship between intestinal microbiota and metabolic diseases (obesity, diabetes, metabolic syndrome, etc.) and intestinal disorders [inflammatory bowel disease, colorectal cancer, irritable bowel syndrome (IBS), etc.]. Few investigations on microbiota have been conducted within the upper gastrointestinal tract (esophagus, stomach and duodenum). The upper gastrointestinal microbiota is essential for several gastrointestinal illnesses, including esophagitis, Barrett’s esophagus, and esophageal carcinoma, gastritis and gastric cancer, small intestinal bacterial overgrowth, IBS and celiac disease. However, the constitution and diversity of the microbiota in different sections of the upper gastrointestinal tract under health and various disease states, as well as the function of microbiota in the pathogenesis of various digestive diseases are still undefined. The current article provides an overview of the recent findings regarding the relationship between upper gastrointestinal microbiota and gastrointestinal diseases; and discusses the study limitations and future directions of upper gastrointestinal microbiota research.