Metagenomic analysis of gut microbiota of patients with colorectal cancer at the Federal Medical Centre (FMC), Abeokuta, Ogun State, Nigeria.

195 Background: It has been suggested that the intestinal microbiome plays a vital role in the development of colorectal cancer (CRC), but the changes in intestinal bacteria in healthy and CRC subjects have not yet been examined in the Nigerian population. The study sought to investigate changes in intestinal bacteria in healthy subjects and patients with CRC. Methods: Fecal samples were collected from healthy and CRC subjects at the Federal Medical Centre, Abeokuta with the study ethical approval number FMCA/47O/HREC/01/2021/23. We extracted genomic DNA with magnetic bead extraction and sequenced the whole genome using a Nanopore MinION sequencer. We performed metagenomic analysis on fecal samples from 20 healthy subjects and 20 patients with colorectal cancer (CRC) to study the bacterial community structure, relative abundance, differentially abundant bacteria, association networks, taxonomic profiling, and specialty gene expression. Results: CRC patients have significantly different bacterial community structures compared to healthy subjects. Compared to healthy subjects, CRC patients had low intestinal bacterial diversity. Only CRCs contain Gammaproteobacteria at the phylum level. Compared to CRC, Bacteroidia and Actinobacteria were significantly more abundant in healthy subjects, while Bacilli and Negativicutes were significantly less abundant. Bacteroides and Prevotella are more abundant in healthy subjects than in CRC at the genus level. There was a greater abundance of Escherichia and Pseudomonas in CRC as compared with healthy subjects. It is noteworthy that Escherichia coli, which co-occurred in both healthy and CRC subjects, was significantly elevated only in CRC, while Pseudomonas aeruginosa only occurs in CRC. Based on phylogenetic analysis, there were notable relationships between six strains of E. coli and four strains of Shigella sp. identified in CRC. There were several pathogenic-associated virulent and antimicrobial resistant genes expressed in these strains. These genes conferred resistance via antibiotic inactivation, efflux pump activity, alteration of cell wall proteins, and regulation of antibiotic permeability. Conclusions: The present study demonstrated that the taxonomic composition and functional genes of intestinal bacteria were significantly altered in CRC. Also, E. coli and P. aeruginosa are at least partially involved in the pathogenesis of CRC.