An increase in Fusobacterium is associated with the severity of oral mucositis after radiotherapy.

Radiotherapy is a common treatment for head and neck cancer but often causes oral mucositis, which reduces quality of life. Recent studies suggest that radiotherapy affects the oral microbiota, but whether it contributes to the severity of mucositis has been unclear. This study investigated the association between radiotherapy-induced changes in the oral microbiota and the severity of mucositis using 16 S rRNA gene sequencing. Oral samples were collected before, during, and after radiotherapy and were analyzed for changes in bacterial composition and diversity using the Shannon index and Chao1 index. Severity of mucositis was assessed, and its association with changes in bacterial groups was investigated. In total, 43 patients participated in the study. Fusobacterium was significantly increased in the group with severe mucositis (p = 0.020), with an occupancy rate of more than 7% after radiotherapy and a positive correlation with severity of mucositis (p = 0.042). There was a significant increase in the Chao1 index after radiotherapy (p = 0.001) but not in the Shannon index. Changes in oral microbiota may determine the severity of radiotherapy-induced mucositis. An increase in Fusobacterium was found to be closely associated with the severity of mucositis and should be controlled to prevent radiotherapy-induced mucositis in head and neck cancer patients.