<scp>IL</scp> ‐ <scp>17A</scp> Inhibitors Therapy Affect Oral Fungal and Bacterial Microbiome in Psoriasis

Psoriasis is a chronic inflammatory skin disease in which the IL-23/Th17/IL-17 axis plays a central pathogenic role while also contributing to antifungal defence. IL-17-targeting biologics such as secukinumab and ixekizumab are increasingly used in its management. This study aimed to characterize changes in the diversity and composition of oral fungal and bacterial communities in psoriasis patients before and after treatment with IL-17 inhibitors. Oral swabs were collected from psoriasis patients at baseline and after 3 months of IL-17 inhibitor therapy, as well as from healthy controls. Direct microscopy and fungal culture were performed. Microbial DNA was extracted and subjected to amplicon sequencing of the fungal ITS1 region and the bacterial 16S rRNA V3-V4 region using the Illumina HiSeq platform. A total of 36 patients and 38 healthy controls were enrolled in this study. Fungal microbiome analysis revealed significantly increased alpha diversity after treatment compared with baseline (p < 0.05), accompanied by markedly elevated beta diversity (p < 0.001). The dominant fungal genera were Blumeria, Pichia and Aspergillus. The relative abundance of Candida was significantly higher in psoriasis patients at baseline than in controls (16.00% vs. 6.43%, p < 0.05) and decreased significantly after therapy (6.12%, p < 0.05). In the bacterial microbiome, beta diversity decreased significantly following treatment (p < 0.001), whereas alpha diversity increased (p < 0.05). The predominant bacterial genera were Streptococcus, Neisseria and Rothia. After treatment, the relative abundance of Haemophilus was significantly lower than at baseline (9.18% vs. 10.14%, p < 0.05). Streptococcus showed a higher trend in patients versus controls (29.74% vs. 16.48%) and declined post-treatment (23.71%). In conclusion, IL-17 inhibitor therapy in psoriasis alters the oral fungal and bacterial microbiota, with notable shifts in Candida, Haemophilus and Streptococcus. These findings provide new insights into the oral microbial changes associated with biologic therapy and may inform clinical monitoring of mucocutaneous microbial imbalance during treatment.