# Characterization of the Gastric Antrum Microbiome in Helicobacter pylori-Negative Individuals: Insights from a Greek Population Using 16S rRNA Next-Generation Sequencing

## TL;DR

This study characterizes the stomach microbiome in Greek individuals without Helicobacter pylori, revealing a diverse microbial community dominated by Proteobacteria and Firmicutes.

## Contribution

The study provides a detailed taxonomic profile of the gastric antrum microbiome in a Greek population negative for H. pylori.

## Key findings

- The gastric microbiome included 19 phyla, with Proteobacteria, Firmicutes, and Bacteroidetes as the most prevalent.
- Streptococcus, Helicobacter, and Prevotella were the most abundant genera in the studied population.
- Alpha diversity indices showed moderate richness and evenness across samples.

## Abstract

Background: Once considered a sterile organ, the human stomach is now known to harbor a diverse microbial community that may influence both gastric homeostasis and disease. While extensive research has been conducted worldwide, regional variation in the gastric microbiome remains insufficiently characterized. This study aimed to describe the gastric antrum microbiome of Helicobacter pylori-negative Greek adults using 16S rRNA next-generation sequencing (NGS). Methods: Samples of gastric biopsies were obtained from patients undergoing gastroscopy at a tertiary hospital in Greece. H. pylori infection was excluded through a combination of bacterial culture and patient medical history. The final study group consisted of 9 subjects. Following DNA extraction, the 16S rRNA gene was sequenced on the Ion Torrent™ platform. Bioinformatic processing and statistical analyses were performed using the phyloseq, vegan, and ggplot2 R packages. Microbial composition, relative abundance, and alpha diversity (Shannon and Inverse Simpson indices) were evaluated at the genus level. Results: The gastric microbiome comprised 19 phyla, 150 families, 213 genera, and 391 species. The predominant phyla were Proteobacteria (36.92%), Firmicutes (34.21%), and Bacteroidetes (12.97%). The most prevalent families were Streptococcaceae, Helicobacteraceae, Prevotellaceae, and Pasteurellaceae. At the genus level, Streptococcus (21.71%), Helicobacter (18.39%), and Prevotella (9.99%) accounted for nearly half of the total relative abundance. Alpha diversity indices indicated moderate richness and evenness across samples. Conclusions: The gastric antrum microbiome of H. pylori-negative Greek individuals exhibits substantial taxonomic diversity dominated by Proteobacteria and Firmicutes. The microbial community structure aligns closely with profiles reported in other global populations. These findings provide a reference baseline for future comparative analyses involving H. pylori-positive individuals to better understand microbiome shifts associated with colonization and gastric disease.