Abstract
BACKGROUND: The role of the gut microbiome and specific enteric bacteria in influencing the development of colorectal cancer (CRC) remains incompletely understood. Recently, it was shown that human CRC-derived strains of Clostridioides difficile were capable of inducing colonic tumorigenesis in a susceptible mouse model. We hypothesized that C. difficile contributes to the pathogenesis of human CRC and would be enriched in CRC tumors compared to paired normal tissues from the same individual. METHODS: We analyzed matched tumor/normal tissue samples from a cohort of 108 individuals presenting to a tertiary care hospital in Kuala Lumpur, Malaysia, for CRC resection between 2013 and 2014. We assessed the prevalence of C. difficile detection using 16S rRNA amplicon sequencing with high-resolution taxonomic assignment as well as culture and PCR. RESULTS: We found that detection of C. difficile was prevalent (38% of individuals), but of low abundance (tumor median relative abundance 0.01%, paired normal 0.006% [P = .4]). Detection of C. difficile was more prevalent in individuals with biofilm-positive tumor tissues than biofilm-negative (ie, 81% of C. difficile-positive individuals were biofilm-positive vs 63% of C. difficile-negative individuals [P = .04]). Additionally, in exploratory analyses, we describe patterns of taxonomic and inferred functional pathway differences between C. difficile-positive and C. difficile-negative groups. CONCLUSIONS: These findings suggest that C. difficile is frequently present in low abundance in the tumor microbiome with a potentially significant impact on community composition and function.