Involvement of Oral Microbiota in the Gut Microbiota of Colorectal Cancer

Background: The oral microbiota is reportedly associated with the gut microbiota and influences colorectal cancer (CRC) progression; however, the details remain unclear. Methods: This study included 52 patients diagnosed with CRC and 51 healthy controls. Saliva and stool samples were collected, and microbiota were evaluated using 16S rRNA analysis and next-generation sequencing. Comparative analysis was performed on both groups. Findings: Linear discriminant analysis Effect Size (LEfSe) revealed indigenous oral bacteria, such as Peptostreptococcus, Streptococcus, and Solobacterium spp., were present at a significantly higher relative abundance in CRC patients compared with controls, consistent for both saliva and stool. LEfSe was also performed after the CRC patients were divided into early stage (Stage I, II; n = 26; 50%) and advanced stage (Stage III, IV; n = 26;, 50%) disease. S. moorei was present at a significantly higher relative abundance in the advanced-stage group compared with the early-stage group, again consistent for both saliva and stool. Interpretation: Among the bacterial species whose relative abundance was significantly higher in CRC patients, P. stomatis, S. anginosus, S. koreensis and S. moorei were apparently supplied from the oral cavity, suggesting indigenous oral bacteria may have promoted initiation of CRC carcinogenesis. Furthermore, S. moorei may influence CRC progression. Funding Statement: This research was supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (19K10361)(15H05045). Declaration of Interests: All authors declare no interests. Ethics Approval Statement: The study was conducted in accordance with the “Declaration of Helsinki.” The study protocols were approved by the ethics committee of Kagoshima University. Informed consent was obtained from all the study participants.