Lasting Gammaproteobacteria profile changes characterized hematological cancer patients who developed oral mucositis following conditioning therapy

BACKGROUND: Oral mucositis (OM) is a common side effect of conditioning therapy implemented before hematopoietic stem cell transplantation (HSCT). The role of oral microbiome in OM is not fully elucidated. OBJECTIVE: To determine oral microbiome profile changes post-conditioning in HSCT patients who developed moderate OM, or mild to no OM. DESIGN: Patient groups were: Muc0-1 with OM-score = 0–1 (43 paired samples) and Muc2 with WHO OM-score = 2 (36 paired samples). Bacterial DNA was isolated from oral samples (saliva, swabs of buccal mucosa, tongue, and supragingival plaque) at pre-conditioning (T(0)), post-conditioning mucositis onset (T(Muc)), and one-year post-conditioning (T(Year)). 16S-rRNA gene next-generation sequencing was used to determine the relative abundance (RA) of >700 oral species. Alpha-diversity, beta-diversity and linear discriminant analyses (LDA) were performed Muc2 versus Muc0-1. RESULTS: Muc2 oral microbiome alpha- and beta-diversity differed between T(0) and T(Muc). Muc2 alpha-diversity and Muc0-1 beta-diversity did not differ between T(0) and T(Year). T(0) to T(Muc) LDA scores were significant in Muc2 for Gammaproteobacteria. For Muc2 patients, the average RA decreased for Haemophilus parainfluenza, a species known as mucosal surfaces protector, but increased for Escherichia-Shigella genera. CONCLUSIONS: Post-conditioning OM might contribute to long-term oral microbiome changes affecting Gammaproteobacteria, in HSCT patients.