Helicobacter pylori infection is associated with the co‐occurrence of bacteria in the oral cavity and the gastric mucosa

Abstract Background Pathogens capable of impacting gastrointestinal tract tumor development are located in the oral cavity, but whether these oral bacteria are able to colonize the gastric mucosa in gastric cancer (GC) patients and whether Helicobacter pylori infection can influence this process remains to be established. Methods Microbial 16S rDNA deep sequencing was conducted to characterize bacteria present in paired gastric mucosa and tongue coating samples in 27 patients with superficial gastritis (SG) and 11 GC patients. Results While the overall composition of the gastric mucosa and tongue coating microbiomes differed substantially, certain bacteria were present in both of these communities. The co‐occurrence of bacteria between the tongue coating and gastric mucosa differed significantly between SG and GC patients. Of the 15 most abundant shared oral bacteria genera (the core shared oral bacteria), which were associated with differences in microbiota composition between these tongue coating and gastric mucosa, three were enriched in the gastric mucosa of GC patients relative to SG patients, whereas, 12 were depleted in GC patient samples. Furthermore, the prevalence and relative abundance of these core shared oral bacteria in the gastric mucosa were also linked to H . pylori infection status, and the core shared oral bacteria were also associated with the overall composition of the gastric mucosal microbiome. Conclusions Helicobacter pylori infections are linked to the co‐occurrence of bacteria in the oral microbiome and the gastric mucosal microbiome. Ectopic colonization of oral microbes may be a primary driver of H . pylori ‐induced gastric microbial dysbiosis in patients with GC.