Metagenomic Evaluation of Oral Microbiota in Patients Affected by Oral Lichen Planus: A Pilot Study

Objective To characterize the oral bacterial and fungal microbiota of symptomatic oral lichen planus patients undergoing topical corticosteroid therapy and to explore microbial patterns potentially associated with subsequent oral candidiasis.Methods Twelve patients with clinically and histologically confirmed OLP were enrolled. Unstimulated saliva and tongue dorsum swabs were collected at baseline and weekly for three weeks during betamethasone therapy. Bacterial communities were profiled using shallow shotgun metagenomics analyzed with METAnnotatorX2, and fungal communities through ITS sequencing and QIIME 2 workflows. Beta-diversity analyses assessed the effects of time, clinical variables, and later candidiasis development. Associations between bacterial taxa and Candida abundance were evaluated using Spearman correlations.Results Oral candidiasis developed in three patients (25%). Microbiota composition showed marked inter-individual variability but high intra-subject stability, with no consistent shifts linked to corticosteroid therapy. Commensal taxa such as Streptococcus, Rothia, and Actinomyces were negatively associated with candidiasis and Candida abundance, whereas anaerobic species including Porphyromonas gingivalis, Prevotella multiformis, and Lachnoanaerobaculum gingivalis displayed positive correlations with fungal proliferation.Conclusions Despite overall stability of the oral microbiota during therapy, specific bacterial signatures were associated with subsequent Candida overgrowth. These findings suggest that cross-kingdom interactions may influence susceptibility to corticosteroid-associated candidiasis and warrant validation in larger cohorts.