Objective: Gastric carcinoma development is triggered by Helicobacter pylori . Chronic H. pylori infection leads to reduced acid secretion, which may allow the growth of a different gastric bacterial community. This change in the microbiome may increase aggression to the gastric mucosa and contribute to malignancy. Our aim was to evaluate the composition of the gastric microbiota in chronic gastritis and in gastric carcinoma. Design: The gastric microbiota was retrospectively investigated in 54 patients with gastric carcinoma and 81 patients with chronic gastritis by 16S rRNA gene profiling, using next-generation sequencing. Differences in microbial composition of the two patient groups were assessed using linear discriminant analysis effect size. Associations between the most relevant taxa and clinical diagnosis were validated by real-time quantitative PCR. Predictive functional profiling of microbial communities was obtained with PICRUSt. Results: The gastric carcinoma microbiota was characterised by reduced microbial diversity, by decreased abundance of Helicobacter and by the enrichment of other bacterial genera, mostly represented by intestinal commensals. The combination of these taxa into a microbial dysbiosis index revealed that dysbiosis has excellent capacity to discriminate between gastritis and gastric carcinoma. Analysis of the functional features of the microbiota was compatible with the presence of a nitrosating microbial community in carcinoma. The major observations were confirmed in validation cohorts from different geographic origins. Conclusions: Detailed analysis of the gastric microbiota revealed for the first time that patients with gastric carcinoma exhibit a dysbiotic microbial community with genotoxic potential, which is distinct from that of patients with chronic gastritis.

The amount of host DNA poses a major challenge to metagenome analysis. However, there is no guidance on the levels of host DNA, nor on the depth of sequencing needed to acquire meaningful information from whole metagenome sequencing (WMS). Here, we evaluated the impact of a wide range of amounts of host DNA and sequencing depths on microbiome taxonomic profiling using WMS. Synthetic samples with increasing levels of host DNA were created by spiking DNA of a mock bacterial community, with DNA from a mouse-derived cell line. Taxonomic analysis revealed that increasing proportions of host DNA led to decreased sensitivity in detecting very low and low abundant species. Reduction of sequencing depth had major impact on the sensitivity of WMS for profiling samples with 90% host DNA, increasing the number of undetected species. Finally, analysis of simulated datasets with fixed depth of 10 million reads confirmed that microbiome profiling becomes more inaccurate as the level of host DNA increases in a sample. In conclusion, samples with high amounts of host DNA coupled with reduced sequencing depths, decrease WMS coverage for characterization of the microbiome. This study highlights the importance of carefully considering these aspects in the design of WMS experiments to maximize microbiome analyses.

There are no established predictive markers of progression of gastric preneoplastic lesions. The aim of this study was to analyze the relationship between Helicobacter pylori cagA and vacA genotypes and progression of gastric preneoplastic lesions. This was a follow-up study that carried out in a province of Spain with a high risk of gastric cancer. A total of 312 patients who underwent upper endoscopy with gastric biopsy in 1988-1994 with diagnoses of normal mucosa, non-atrophic gastritis (NAG), non-metaplastic multifocal atrophic gastritis (MAG), and complete or incomplete intestinal metaplasia (IM), and who accepted to undergo a new biopsy during 2005-2007 or had an end point during follow-up, were included in this study. Detection and characterization of H. pylori cagA and vacA genotypes was performed directly in baseline paraffin-embedded gastric biopsy specimens by PCR followed by reverse hybridization onto a line probe assay. Inter- and intra-observer variability of histological diagnosis was assessed. Analysis was done using unconditional logistic regression. The mean age of patients was 48.5 years (45% males) and the mean of follow-up was 12.8 years. H. pylori strains harboring cagA, vacA s1, and vacA m1 genotypes were more frequently found in patients with more advanced gastric preneoplastic lesions. Infection with cagA-positive, vacA s1, and vacA m1 strains was associated with progression of gastric preneoplastic lesions (multivariate odds ratio (OR)=2.28, 95% confidence interval (CI) 1.13-4.58; OR=2.90, 95% CI 1.38-6.13; and OR=3.38, 95% CI 1.34-8.53, respectively). Infection with strains that are simultaneously cagA positive and vacA s1/m1 was associated with progression of gastric precancerous lesions with an OR of 4.80 (95% CI 1.71-13.5) in relation to those infected with cagA-negative/vacA s2/m2 strains. H. pylori genotyping may be useful for the identification of patients at high risk of progression of gastric preneoplastic lesions and who need more intensive surveillance.

H. pylori drug-resistant strains and non-compliance to therapy are the major causes of H. pylori eradication failure. For some bacterial species it has been demonstrated that fatty acids have a growth inhibitory effect. Our main aim was to assess the ability of docosahexaenoic acid (DHA) to inhibit H. pylori growth both in vitro and in a mouse model. The effectiveness of standard therapy (ST) in combination with DHA on H. pylori eradication and recurrence prevention success was also investigated. The effects of DHA on H. pylori growth were analyzed in an in vitro dose-response study and n in vivo model. We analized the ability of H. pylori to colonize mice gastric mucosa following DHA, ST or a combination of both treatments. Our data demonstrate that DHA decreases H. pylori growth in vitro in a dose-dependent manner. Furthermore, DHA inhibits H. pylori gastric colonization in vivo as well as decreases mouse gastric mucosa inflammation. Addition of DHA to ST was also associated with lower H. pylori infection recurrence in the mouse model. In conclusion, DHA is an inhibitor of H. pylori growth and its ability to colonize mouse stomach. DHA treatment is also associated with a lower recurrence of H. pylori infection in combination with ST. These observations pave the way to consider DHA as an adjunct agent in H. pylori eradication treatment.

BackgroundHelicobacter pylori induces an invasive phenotype in gastric epithelial cells through a mechanism that requires the type IV secretion syste