OBJECTIVETo investigate the taxonomic richness and diversity of gut microbiota in patients with colorectal adenoma and elucidate the role of gut microorganisms in precancerous lesions in the colon and rectum.

METHODAdenomatous tissues from 31 patients with colorectal adenoma and normal intestinal mucosal tissues from 20 healthy control subjects were collected through colonoscopy. The total bacterial genomic DNA was extracted, and the V-Vhypervariable region in bacterial 16S rRNA gene was amplified using polymerase chain reaction and sequenced on an Illumina MiSeq platform.

RESULTSPatients with colorectal adenomas had a higher alpha diversity and richness indices compared to the healthy controls (P<0.01). The mucosal microbiota in colorectal adenoma tissue showed a distinctive structural difference from that in normal intestinal mucosal tissues. At the phylum level, a large decrease in Firmicutes with concomitant relative expansion of Proteobacteria was observed in patients with colorectal adenomas, resulting in a significant decrease in the Firmicutes/Bacteroidetes ratio (P<0.01). At the genus level, Lactococcus and Pseudomonas were enriched whereas Enterococcus, Bacillus, and Solibacillus were reduced obviously in the preneoplastic tissues (P<0.01). We also found a similar gut microbiome composition between low-grade and high-grade intraepithelial neoplasia; the ratio of Escherichia-Shigella tended to increase in high-grade intraepithelial neoplasia, but this change was not statistically significant (P%0.28).

CONCLUSIONSignificant changes in the structure of the intestinal flora occur in patients with colorectal adenomas, indicating that the association of dysbiosis of the gut microbiota with the occurrence of a pro-oncogenic microenvironment.