Effect Of Common Helicobacters Infection On Gastric Microbiota

Progress in sequencing technology and biological information analysis methods have enhanced our knowledge of gastrointestinal microbiota independent of traditional culture methods.The human stomach was long erroneously assumed to be sterile because of the gastric acid barrier.However,the discovery of Helicobact.er pylori dispelled this dogma and opened the field for exploring the gastric microbiome.Increasing evidence suggests that the stomach possess a distinct and complex ecosystem inhabited by a wide variety of bacteria.Homeostasis of the stomach microecology is crucial for maintaining health,and its perturbation is considered to be a trigger of various stomach diseases.H.pylori,as the most relevant inhabitant,plays an important role in altering the gastric microenvironment by inhibiting acid secretion,leading to an imbalance in hormones,which might facilitate transient flora survival and colonization on the gastric epithelium,with subsequent disruption of the established gastric microbiota.Limited research has led to a consensus that the presence of H.pylori dramatically affects species richness and the evenness of the gastric microbiota and does not change taxonomic diversity.The investigation of the human gastric microbiota is still in its infancy,and the roles and functions of other bacteria should be further elucidated.In addition to Helicobacter pylori,other members of the genus Helicobacter,i.e.,gastric non-pylori Helicobacter(NHPH)species,are also associated with a range of gastric diseases.The dysbiosis of the gastric microbiota plays an important role in the development of gastric disease.However,due to the fastidious nature of these organisms,the effects of NHPH species on the structure and function of gastric microbiota are difficult to assess.Progress in sequencing technology makes this research possible.5 Moreover,previous studies have shown that saliva is the main source of microbial communities in the stomach,but whether these bacteria can be planted in the gastric mucosa is still unknown.Whether salivary bacteria can change the structure of gastric mucosal flora and how to change the structure of gastric mucosa,still need to further investigate.Part 1:Effect of common Helicobacters infection on the structure and function of gastric microbiotaIn this study,we investigated the effects of NHPH species(H.suis,H.felis or H.salomonis)and H.p.ylori coinfection on the stomach microbial composition of gastric mucosa specimens from patients with gastric disorders by applying 16S rRNA gene deep sequencing.The species-specific influence of NHPHs on the structure of the gastric microbiota was indirectly characterized by comparing variations between H.p.ylori mono-and coinfection samples.In addition,we predicted gene functions and metabolic pathways associated with variations in the gastric bacterial community between the H.pylori mono-and coinfection groups.We found marked structural and functional variations in the gastric microbiota between H.pylori mono-and coinfection samples.Compared with the H.pylori monoinfection(H.pylori only)group,both the HPHS and HPHF(H.pylori/H.suis and H.pylori/H.felis coinfections,respectively)groups showed significant increases in phylotype richness and significant decreases in β diversity,but the HPHM(H.pylori/H.salomonis coinfection)group did not.Regarding the top five phyla and top thirty-five genera,the HPHS and HPHF groups had similar variation trends in relative abundance.The increased relative abundance levels of the genera Vibrio,Pseudoalteromonas,Photobacterium and Clostridium may be associated with increases in predicted signal transduction/metabolic pathways among the three coinfection groups.The relative abundance levels of bacteria involved in the formation of N-nitroso compounds were significantly decreased in the HPHS and HPHF groups,including the genera Streptococcus,Prevotella,Escherichia,Neisseria,Pseudomonas,Haemophilus,Campylobacter,Veillonella,Lactobacillus,Clostridium and Bacteroides.The significantly decreased relative abundance levels of the phyla Firmicutes and Bacteroidetes in the HPHS and HPHF groups may be associated with the observed increases in predicted lipid metabolism pathways.To the best of our knowledge,this is the first time the effects of NHPH species on the gastric microbiota have been explored using 16S rRNA gene sequencing.The results in this study implied that NHPH can arouse the variation of structure and function of gastric microbiota,which may pave the way to further research on the pathogenesis of gastric diseases.Part 2:Characteristics of salivary microbiota and the effect of core microbiota on gastric microbiotaIn this study,the differences in the structure of salivary microbiota between Helicobacter pylori positive and negative individuals were compared by 16S rDNA sequencing.At the same time,we compared the differences between saliva core microbiota and gastric core microbiota.The study found that the relative abundance of dominant bacteria had no significant difference between the two groups(non-parametric t-test,p>0.05).The results showed that there was no significant difference between the two groups in the community richness and community diversity(Monte Carlo permutations,p>0.05).Anosim analysis and MRPP analysis showed that there was no significant difference both within-groups and between-groups.Therefore,there was no significant difference in the structure of salivary bacteria between Helicobacter pylori positive individuals and negative individuals.In order to explore the effect of salivary core microbiota on gastric bacteria community,we compared the stucture of core microbiota among H.pylori positive saliva(SH group),H.pylori negative saliva(SN group),H.pylori positive gastric mucosa(GH group)and H.pylori negative gastric mucosa(GN group).Comparison of the top twenty phylum among groups showed that significant difference was found in the relative abundance of twelve phylum in the gastric mucosa samples and saliva samples,including Proteobacteria,Firmicutes,Bacteroidetes,Fusobacteria,Actinobacteria,Acidobacteria,Gemmatimonadetes,Chloroflexi,Spirochaetes,Tenericutes,Cyanobacteria,Euryarchaeota.The result of a diversity index showed that the gastric mucosa group was significantly higher than the saliva group in the community richness.In the respect of community diversity,comparison among four groups was showed below,GN group>SN group>SH group>GH group.NDMS and MRPP results further show that the structure of the flora and the structure of the flora in the stomach are significantly different(p<0.01).Therefore,there was no significant difference in a-diversity,P-diversity and inter-species species between saliva microbiota from the HP group and the HN group.The structure of the saliva bacteria community was not affected by Helicobacter pylori infection status.Alpha diversity of gastric microbiota in healthy individuals(HP negative)was significantly higher than that in saliva samples.The core microbiota of saliva samples was significantly different from that of gastric core microbiota.The community structure has a significant variation.