Changes in oral microbiota after the initiation of chemotherapy in patients with hematopoietic tumors

Background Recently, the gut microbiota has been shown to play an important role in the response and resistance to chemotherapy. Although there is much knowledge about chemotherapy-induced changes in the gut microbiota, chemotherapy-associated changes in the oral microbiota remain unclear. Herein, we aimed to evaluate the changes in oral microbiota associated with the initiation of chemotherapy in patients with malignant hematopoietic tumors. Methods Oral samples were collected before and 8–20 days after the start of chemotherapy from 50 patients with malignant hematopoietic tumors who were starting chemotherapy for the first time. The 16S ribosomal RNA gene sequencing of bacterial DNA extracted from oral samples was performed to compare the oral microbiota before and after the initiation of chemotherapy. Results The richness or evenness of diversity in the ‘after start of chemotherapy’ group decreased significantly, compared with the ‘before start of chemotherapy’ group (alpha-diversity; observed operational taxonomic units (OTUs) index, p p p = 0.001; and weighted UniFrac distances, p = 0.003). Linear discriminant analysis effect size analysis demonstrated an increased abundance of species of certain genera, such as Staphylococcus, and decreased abundance of species of some genera, such as Streptococcus and Neisseria, in the ‘after-chemotherapy’ group, compared with those in the ‘before-chemotherapy’ group. The amounts and trends of change in the oral microbiota before and after the start of chemotherapy differed among the subjects. Of the 25 bacterial genera whose prevalence changed significantly before and after the start of chemotherapy, the proportion of oral commensals such as Streptococcus and Neisseria decreased in many subjects. In contrast, Staphylococcus and Pseudomonas were detected only in a few subjects, but their relative abundance increased significantly after the start of chemotherapy. Conclusions The oral microbiota of patients with hematopoietic tumors changed markedly after the initiation of chemotherapy. Our findings are expected to aid the elucidation of the pathogenesis of oral mucositis, which is an adverse event of chemotherapy, and the development of treatment methods for this condition.