Association of Oral Microbiota with Digestive Tract Cancers

Objectives: It is well known that oral microbiota is related to oral health. In addition, oral microorganisms are constantly swallowed with saliva and delivered to our whole body through digestive tract; therefore, it is reasonable that they relate to gastrointestinal diseases suspected of bacterial implication as well as oral diseases. This study examined salivary microbiota composition of patients with digestive tract cancer and evaluated their difference by cancer site.
Methods: We collected saliva samples from 59 patients with cancer of digestive tract (tongue/pharynx, esophagus, stomach, and colon) and 118 age and sex matched healthy controls. We compared the bacterial diversity and composition of salivary microbiota by 16S ribosomal RNA gene sequencing. The detection of discriminant bacterial species was performed using the linear discriminant analysis effect size (LEfSe) method.
Results: Salivary bacterial diversity (number of observed bacterial species) in patients was significantly higher than that in controls (P < 0.01). By cancer site, saliva from patients with tongue/pharyngeal and esophageal cancer demonstrated significantly higher bacterial diversity (both P < 0.01) and Streptococcus salivarius and Veillonella atypica were differentially abundant compared to controls. On the other hand, although there was no significant difference in bacterial diversity between patients with stomach and colon cancer and controls (P = 0.94, 0.49, respectively), Actinomyces odontolyticus and Streptococcus parasanguinis were differentially abundant in them compared to controls.
Conclusions: These results suggest that salivary microbiota is associated to digestive tract cancers and its effect varies depending on the distance from oral cavity.