Is Helicobacter pylori infection associated with changes in gastric and intestinal microbiome composition?

Helicobacter pylori infection is convincingly linked to altered gastric microbial ecology and is also associated with differences in stool-measured intestinal microbiota. For a 50-year-old man, these findings describe population-level microbial patterns; they do not make a stool profile a diagnostic or causal test of infection-related microbiome effects.

Clinical and observational evidence

• Gastric-biopsy sequencing studies and systematic reviews consistently find lower bacterial alpha diversity and distinct communities in infected stomachs. Profiles often show relative Helicobacter/Proteobacteria dominance with relative reductions in Firmicutes, Bacteroidetes, and Actinobacteria, although this does not prove reduced absolute abundance of those groups.
• Intestinal evidence is more heterogeneous but supports an overall association. In a matched cross-sectional study of 212 H. pylori–positive adults and 212 controls, infection status was associated with higher Shannon and Simpson diversity, beta-diversity differences related to stool-antigen load, and differences in 13 taxa. Other studies found no Shannon-diversity difference or age-dependent patterns, so no single “H. pylori stool signature” is established.

Mechanistic and treatment-related context

• Successful eradication has been associated with increased gastric richness and Shannon diversity, whereas failed treatment was not associated with significant gastric-diversity change.
• Eradication regimens can themselves transiently reduce stool richness and produce regimen-dependent bacterial changes, with variable or incomplete recovery. PPIs also independently associate with fecal microbiome changes. These effects make post-eradication stool shifts unsuitable for attributing changes specifically to removal of H. pylori.

Interpretation

• Cross-sectional stool profiles cannot establish temporal sequence, exclude reverse causality, or fully control for diet, age, geography, gastrointestinal disease, prior antibiotics, and PPI exposure.

Bottom line

• H. pylori is strongly associated with gastric microbiome alteration and moderately associated with intestinal compositional differences, but observational stool data cannot show that the infection caused those intestinal changes.