The composition of gastric microbiota is determined by the status of Helicobacter pylori infection. In subjects who have never been infected by H. pylori, gastric microbiota includes various bacteria, creating ideal microbial diversity. This ideal microbial diversity is destroyed by H. pylori infection at low intragastric pH. Since it is difficult for most bacteria to proliferate within an acidic stomach, relative H. pylori abundance gives rise to microbial dysbiosis. Conversely, unideal microbial diversity is often observed in infected individuals with impaired gastric secretory ability at hypochlorhydric condition. Bacteria producing carcinogenic N-nitrosamine compounds are often detected in individuals with past or chronic H. pylori infection at high intragastric pH. Nonetheless, microbial imbalance that occurs in the earlier phase before gastric carcinognenesis is uncertain.

Dominant colonization of a specific microbiota leading to dysbiosis may lead to inflammation of the mucosa. We hypothesized that the degree of inflammation depend on the composition of microbiota. This study was aimed to define gastric and duodenal microbiota leading to abnormal histopathology. We further tried to elucidate whether the composition of duodenal microbiota is altered by gastric microbiota.

Among the dyspeptic subjects who visited for upper gastrointestinal (UGI) endoscopy, subjects with drug intake (antibiotics, PPIs, laxatives, antidepressants, statins, metformin) within 3 months will be excluded. Three biopsies will performed at the greater curvature side of the mid-antrum, greater curvature side of the mid-body, and at the duodenum, respectively. Next generation sequencing analysis will be performed for 16S rRNA variable regions using the biopsied samples.

Primary study endpoint is 16S rRNA sequencing findings of gastric and duodenal microbiota.

Secondary endpoints are microbiota linked with higher degrees of inflammation, activity, atrophy and intestinal metaplasia based on the updated Sydney classification. Furthermore, correlation between the microbiota and endoscopy finding will be analyzed.

Inclusion Criteria:

• Dyspeptic subjects who visited for evaluation including upper gastrointestinal endoscopy and biopsies
• Age >20 years old

Exclusion Criteria:

• Underlying disease(s) that requires managements
• Recent intake of drug(s)
• History of gastrectomy

Dyspeptic subjects for analysis