Species-level dynamics of gastric microbiome after Helicobacter pylori eradication in high-risk Mongolian population

Species-level resolution is essential to understand gastric microbiome recovery after Helicobacter pylori eradication, yet short-read 16 S rRNA approaches often obscure clinically relevant changes.

Gastric biopsies from 121 adults in Bayan-Ölgii, Mongolia (71 H. pylori-positive, 50 H. pylori-negative) were analyzed, including nine paired pre- and post-eradication gastric biopsy samples collected six months apart, enabling exploratory longitudinal analysis. Full-length 16 S rRNA (V1-V9) sequencing was performed using the Oxford Nanopore platform with EMU taxonomic assignment (SILVA v138.1/NCBI RefSeq). Ecological changes were evaluated using diversity indices, principal coordinates analysis (PCoA) with PERMANOVA, and differential abundance testing (DESeq2, FDR < 0.05). Eradication therapy (esomeprazole-bismuth-doxycycline-levofloxacin) achieved success in 54 of 57 H. pylori-positive patients (94.7%).

H. pylori-positive microbiomes were dominated by H. pylori (91.8% ± 3.9%) and exhibited markedly reduced diversity (Shannon = 0.44 ± 0.11) compared with H. pylori-negative samples (2.08 ± 0.25; p < 0.001). Six months after eradication, diversity increased significantly (2.17 ± 0.20; p = 0.0001), with enrichment of oral commensals including Streptococcus mitis (↑ 11.9×), Neisseria elongata (↑ 13.7×), and Prevotella melaninogenica (↑ 13.0×). However, post-eradication profiles at six months remained distinct from H. pylori-negative communities (PERMANOVA R² = 0.12; p = 0.02). In total, 174 amplicon sequence variants changed significantly, including persistence of Fusobacterium nucleatum.

Nanopore full-length 16 S sequencing reveals fine-scale, clinically relevant shifts that are masked by partial-gene assays. Eradication rapidly restores microbial diversity, but at six months, is associated with a novel ecological equilibrium rather than complete normalization. This species-resolved approach offers a practical framework for post-eradication microbiome monitoring and may inform strategies to reduce residual gastric cancer risk in high-burden populations.