Helicobacter pylori is the most dominant and clinically relevant member of the human gastric microbiota that it may be considered a natural member of it as only a small proportion of H. pylori-colonized humans develop disease. At phylum level, the gastric microbiota is mainly comprised of Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria and Fusobacteria, both in H. pylori-positive and -negative individuals, but with different percentages of relative abundance. Helicobacter is the major genera followed by Streptococus, Prevotella, Neisseria, Veillonella, Fusobacterium, and Haemophilus in the H. pylori-colonized stomach of humans, whilst Streptococcus and Prevotella are the most predominant in the H. pylori-negative stomach. Helicobacter, Streptococcus, Prevotella, and Fusobacterium are among the most predominant genera colonizing the human stomach, when transcriptionally active bacteria were studied.

The papers published between 2021 and 2022 confirmed the H. pylori dominance in the non atrophic stomach microbiome and a progressive dysbiosis occurred as result of the cascade of histological changes toward gastric carcinogenesis, but a unique gastric cancer associated microbiome profile has not been consistently identified. Colonization with bacteria other than H. pylori may contribute to perpetuating chronic inflammation and to increasing gastric cancer risk.