Microbiome Signatures in a Fast and Slow Progressing Gastric Cancer Murine Model and Their Contribution to Gastric Carcinogenesis

Gastric cancer is the third most common cancer in the world and Helicobacter spp . being one of the main factors responsible for development of cancer. Alongside Helicobacter the microbiota of the stomach mucosa may also play an important role in gastric cancer progression. Previously we had established that MyD88 deficient mice rapidly progressed to neoplasia when infected with H. felis . Thus, in order to assess the role of microbiota in gastric cancer progression we measured the changes in microbial diversity of the stomach in mice with different genotypic backgrounds (Wild type (WT), MyD88 deficient (MyD88−/−), mice deficient in the Toll/IL-1R (TIR) domain-containing adaptor-inducing interferon-β (TRIF, Trif lps2), and MyD88 and Trif deficient (MyD88−/− and Trif−/−)double knockout (DKO) mice), both in uninfected and Helicobacter infected mice and its correlation of these changes with gastric cancer progression. We observed that there was an overall reduction in microbial diversity post infection with H. felis across all genotypes. Campylobacterales were observed in all infected mice, with marked reduction in abundance at 3 and 6 months in MyD88−/− mice. This low abundance of H. pylori could facilitate dominance of other organisms of microbiome like Lactobacilliales . A sharp increase in Lactobacilliales in infected MyD88−/− and DKO mice at 3 and 6 months was observed as compared to Trif−/− and WT mice suggesting its possible role in gastric cancer progression. This was further reinforced upon comparison of Lactobacillus ratio with histological data suggesting that Lactobacillales is closely associated with Helicobacter infection and gastric cancer progression. Thus, this study firstly suggests that difference in genotypes could define the stomach microbiome and make it more susceptible to development of gastric cancer upon Helicobacter infections. Secondly the increase in Lactobacillales could contribute to faster development of gastric cancer and serve as a probable bio marker for fast progressing form of gastric cancer. ### Competing Interest Statement The authors have declared no competing interest. * H. pylori : Helicobacter pylori WHO : World Health Organization Myd88−/− : Myeloid differentiation primary response 88- deficient H. felis : Helicobacter felis Trif−/− : TIR-domain-containing adapter-inducing interferon-β WT : Wild Type DKO : double knockout BHI : Brain Heart Infusion QIIME2 : Quantitative Insights into Microbial Ecology OTU : Operational taxonomic unit