Oral microbiome and history of smoking and colorectal cancer.

BACKGROUND: The equilibrium of oral microbiome may be altered by environmental factors, including cigarette smoking. Several recent studies also suggest that oral pathogens causing periodontal disease, such as Fusobacterium nucleatum , are involved in pathogenesis of colorectal cancer.

METHODS: For this study oral rinse DNA samples from 190 participants in a population-based case-control study for colorectal cancer were used to amplify a V3-V4 region of bacterial 16S rRNA gene. The amplicons were sequenced using Illumina MiSeq paired end chemistry on two runs, yielding approximately 35 million filtered reads which were assigned to bacterial phyla.

RESULTS: No association was found between Fusobacterium abundance or presence and colorectal cancer. However, adjusted for age and experimental batch, colorectal cancer history was associated with increased presence of genus Lactobacillus and increased relative abundance of Rothia by 28% and current smoking was associated with a 33% decrease in relative counts of Betaproteobacteria (primarily Neisseria ) and 23% increase in relative abundance of Veillonellaceae family. We also found that smoking had significant effects on the 2nd component scores and 2nd coordinate distances in principal component and coordinate analyses.

CONCLUSIONS: It remains to be elucidated whether the observed differences can be translated into biochemical changes in oral environment, thus potentially affecting oral health.