Analysis of the intestinal microbiome in colorectal cancer

Abstract

Aim. To conduct a comparative analysis of the microbiome of biopsies of a tumor and normal intestinal epithelium of patients diagnosed with colorectal cancer and to identify of functional activities of the obtained bacterial isolates that affect the development of the tumor. Methods. The study included 50 patients with malignant neoplasms of the colon: 36 men and 24 women. The mean age of the patients was 64.1±10.2 years. To analyze the microbiota of the biopsies, DNA samples were obtained from the tissue of the unaffected colon mucosa and tumor of the patients. Bacterial 16S rRNA genes fragments were amplified using bar-coded primer bakt_341f. Metagenomic next-generation sequencing was performed using the MiSeq platform (Illumina, USA). The obtained data were processed by bioinformatic methods using the QIIME package. Recognition of microorganisms depending on the morphotype and gram staining of the microflora was carried out using combination differential media and biochemical tests. Statistical analysis was carried out using Microsoft Excel, Service Pack 2 for Office XP, Statistica 6.0 (StatSoft). A comparative analysis was performed with the Student's t-test and the Mann-Whitney test in case of unmet conditions of validity. Alpha diversity of bacterial communities was quantified by the Shannon diversity index and the UniFrac distance for beta diversity analysis. Results. In patients with colorectal cancer, 5 bacterial phyla were isolated, the predominant of which were Firmicutes and Bacteroidetes, while the content of Actinobacteria was low. In addition, a higher number of representatives of Fusobacteria was observed in the tumor tissue compared to the tissue of a healthy mucosa, at a distance of 5 centimeters proximal to the tumor. The results of this study indicate that the microbiome of a tumor and a healthy mucosa fundamentally differ from each other not only in morphotype and gram staining but also in antagonistic, hemolytic and ribonucleolytic activities. Conclusion. Colonization of the tumor by dominant aggressive Gram-negative bacteria leads to significant changes in the tumor microbiome composition compared with normal mucosa, whose representatives are displaced from the damaged epithelium by more aggressive strains.