Salivary Microbiota and Network Alterations in Oral Lichen Planus with Candida Compared to Healthy Controls

Background: Oral lichen planus (OLP) is a chronic immune-mediated mucosal disorder frequently accompanied by Candida colonization. However, the polymicrobial interactions and network alterations underlying this association remain poorly understood. This study aimed to characterize bacterial–fungal community changes and interkingdom network dynamics in OLP patients with Candida detection compared to healthy controls. Methods: Unstimulated saliva samples were collected from 24 OLP patients and 31 healthy controls. Bacterial 16S rRNA (V1–V2) and fungal ITS2 regions were simultaneously sequenced using Illumina NovaSeq. Taxonomic profiling, diversity analyses, differential analysis, and intermicrobial correlations were analyzed. Results: Beta diversity analysis revealed distinct community separation between groups (p = 0.001). OLP exhibited increased Bacteroidetes and decreased Firmicutes compared to controls. Health-associated commensals (Streptococcus salivarius, Rothia mucilaginosa, Haemophilus parainfluenzae, Veillonella sp. HMT 917) were significantly depleted, while pro-inflammatory anaerobes (Prevotella, Fusobacterium, Leptotrichia, Selenomonas) were enriched. At the genus level, Candida abundance was modestly higher in the OLP group (1.38%) compared to Healthy (0.94%), and Candida albicans was the most prominent fungal species, with a mean relative abundance of 1.22% in OLP compared to 0.91% in Healthy controls, calculated using the same sample-level denominator as the genus-level values above. Network analysis demonstrated that Candida occupied a central position with expanded connectivity to disease-associated genera. The disease network showed increased negative correlations and dispersed topology, reflecting inversely correlated taxa and reduced modularity (0.206 vs. 0.260 in healthy), consistent with less distinct community compartmentalization. Conclusions: OLP is characterized by compositional dysbiosis and disrupted bacterial–fungal interaction networks. Candida may function as a network hub associated with interkingdom dysbiosis in OLP. These findings suggest that microbiome-targeted adjunctive therapies—including antifungals, selective antimicrobials, and probiotics—warrant investigation for managing Candida-associated OLP.