Oral bacteriome in pediatric patients with malignancies prior to chemotherapy: a pilot study using full-length 16S rRNA sequencing.

Objective: To characterize the composition, diversity, and ecological features of the oral bacteriome in pediatric patients with malignancies prior to chemotherapy initiation. Methods: In this prospective pilot study,supragingival plaque samples were collected from 10 pediatric cancer patients prior to the initiation of chemotherapy. Bacterial genomic DNA was extracted from each sample, and the full-length 16S rRNA gene was amplified and sequenced on the PacBio Sequel II platform using circular consensus sequencing (CCS). Raw CCS reads were quality-filtered and denoised into amplicon sequence variants (ASVs) using DADA2, and taxonomic assignment was performed against the SILVA 138 reference database. Alpha diversity was assessed using the Chao1, Shannon, Simpson, and Faith's phylogenetic diversity (PD whole tree) indices, while beta diversity was evaluated through principal coordinate analysis (PCoA), and non-metric multidimensional scaling (NMDS). Microbial co-occurrence networks were constructed to characterize bacterial interactions, and functional potential was predicted using PICRUSt2, and BugBase. Results: A total of 614,473 high-quality CCS reads were generated, yielding 1,697 ASVs. Alpha diversity analysis revealed substantial inter-individual variation in microbial richness and diversity among the pediatric cancer patients. The bacterial community was dominated by the phyla Conclusion: These preliminary findings reveal a taxonomically diverse, highly individualized pre-chemotherapy oral bacteriome, providing foundational baseline profiles to guide future longitudinal investigations of chemotherapy-induced dysbiosis and personalized interventions.