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Gastric Polyposis Samples Marked by Microbial Community Shifts

NEW YORK (GenomeWeb) – New research is suggesting that lower-than-usual gut microbial diversity and other types of dysbiosis in gastric mucosa samples coincide with gastric polyposis — a propensity for non-cancerous stomach polyps that may progress to cancer in rare cases.

"The diversity of the gastric flora in patients with gastric polyps was significantly lower than that of healthy people, and the intragastric bacterial composition between the two groups was significantly different," corresponding author Yunsheng Yang, a gastroenterology and hepatology researcher at the Chinese PLA Medical College, and his colleagues wrote in a study published online today in Scientific Reports.

The researchers used 16S ribosomal RNA gene sequencing to profile the microbial communities in gastric mucosal biopsy samples from dozens of gastric polyposis cases or unaffected controls. In addition to detecting decreased microbial diversity in the gastric polyposis group, they subsequently demonstrated that a microbial dysbiosis index (MDI) developed from the 16S rRNA sequence data could differentiate between individuals with or without gastric polyposis.

"The MDI index could be used as a biomarker of microbial indicators of [gastric polyposis] in future clinical applications and it may predict people who have the tendency of having [gastric polyposis]," the authors wrote. "However, there was only a small validation set of data used to assess the performance of this index in the present study, and a larger number of samples are needed to validate this predictive index."

Using Illumina MiSeq instruments, the researchers did 16S rRNA gene sequencing on gastric mucosal or gastric tissue samples collected from 30 individuals with gastric polyposis and 30 unaffected controls. The samples were collected after fasting, they noted, and the participants were not taking medications that might affect their microbiomes.

"[G]astric microbial dysbiosis plays an important role in gastric carcinogenesis, but no studies have investigated the relationship between gastric polyps and the stomach flora," the authors wrote.

Based on millions of reads generated for nearly 150 gastric mucosal or tissue samples, the team identified almost 600 bacterial genera and representatives from 68 phyla, including bugs from the Proteobacteria, Firmicutes, and Bacteroidetes phyla.

The researchers uncovered distinct gastric microbial features in the samples from gastric polyposis cases and unaffected controls, including lower diversity in the polyposis cases and an over-representation of the stomach ulcer-associated microbe Helicobacter pylori in controls. From these findings, and results reported previously, the authors speculated that "the presence of H. pylori may be a protective factor for these benign gastric polyps."

When they set microbial features in samples from the 20 gastric polyposis cases involving fundic gland polyps alongside those from 10 gastric polyposis cases marked by hyperplastic polyps, the researchers saw comparable microbial features. Likewise, they saw relatively few differences in microbial diversity or representation across different gastric sampling sites within the gastric polyposis or control group.

In contrast, the team designed an MDI model that was based on microbes in 104 of the samples that could distinguish gastric polyposis-free and -affected individuals in the remaining 44 samples with more than 93 percent accuracy. 

The MDI "based on the gastric microbiota at the genus level … was able to distinguish between individuals in the [gastric polyposis] and [healthy control] groups," the authors wrote. "These findings showed that intragastric flora dysbiosis may be closely related to the occurrence and development of gastric polyps."

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