The difference of the gut microbiota of gastric cancer in relation to Helicobacter pylori negativity and positivity.

10 Background: Helicobacter pylori (HP) is a major risk factor for gastric cancer, however, only 1-2% of HP(+) people develop adenocarcinoma. In this study, we have compared the intestinal microbiota composition related to HP status among gastric cancer patient using 16SrRNA gene-based metagenomic sequencing analysis and culture-based method. Methods: Stool samples were collected from 18 gastric cancer patients. 16S rRNA genes were sequenced on the Illumina Miseq platform and further analyzed to evaluate the gut bacterial community. The bacteria strains of fecal sample were isolated in aerobic and anaerobic condition. Results: Metagenomics analysis of fecal sample showed four major phyla; Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria were dominant. Firmicutes were the most dominant phylum. Within this phylum, the relative abundance of Clostridiales including Ruminococcus was higher in the HP(-) group, whereas Lactobacillales including streptococcus was higher in HP(+) group. In addition the relative abundance of Bacteroidetes in HP(-) group and Actinobacteria (especially, genus Bifidobacterium) in HP(+) group was observed highly. In the bacterial culture-based approach, bacteria strains belonged to Clostridiales such as Clostridium perfringens, Ruminococcus feacis, Blautia sp., Coprococcus comes were isolated in HP(-) sample. In HP(+) sample, Klebsiella, Bacteroides, Bifidobacterium were isolated. Bacillus species, Escherichia/Shigella was enriched regardless of HP exist. Streptococcus was not cultivated in HP(+) group, but isolated in HP(-) group in contrast with metagenome data. Conclusions: We found the intestinal bacterial diversity in the HP(+) group was lower than those in the HP(-) and the microbial composition was different between HP(+) and HP(-). Metagenome analysis showed the order Clostridiales of the phylum Firmicutes were enriched in the HP(-) group while the order Lactobacillales (specially, Streptococcus) were enriched in the HP(+) group. Compared to isolates between two groups, bacteria species belonged to the order Clostridiales such as Clostridium, Ruminococcus , Blautia , Coprococcus were cultivated particularly in HP(-) sample.