Salivary microbiota injury and oral mucositis. Pretransplantation bacteria correlate with future severe OM. (A) Proportion of OM by the relative abundance of pretransplantation Kingella. Abundance groups are relative to the median, which was 0 and shared by >50% of patients. P value was calculated using the χ2 test. (B) Pretransplantation Kingella relative abundance by OM grade (FDR-corrected *P < .05, **P < .001). (C-F) Paired analysis between 2 samples from the same patient at different time points (before HSCT and 7 days after) across OM groups. (C) There was a significant reduction in the Shannon index between the 2 time points in the grade 3 to 4 OM group (**FDR-corrected P < .01). (D) Bray-Curtis matrix distances between the 2 time points. A large distance indicates greater variation between the 2 time points. The variation was higher in patients with severe OM compared with grade 0 to 1 OM (*FDR-corrected P < .05). (E) Linear discriminant analysis effect size analysis for differences in bacterial composition on days 7 to 13 posttransplantation by OM severity groups (linear discriminant analysis scores >2). (F) Polyamine pathway. Colors represent the log2 fold change of each metabolite from the pathway; left square, grade 3 to 4 OM; right square, grade 0 to 1 OM. Metabolites that changed significantly are marked with a green dot, while the ones that were also significant in MIMOSA2 analysis, capturing changes in microbiome-related metabolites, are marked with a red dot.