Bacterial DNA but not fungal ITS signature is present in the synovial fluid of patients with osteoarthritis.

Emerging evidence suggests that translocation of pathogenic bacteria from the gut to the SF may play a role in the pathogenesis of OA. Although synovial joints were historically regarded as sterile, studies have demonstrated the presence of a low-biomass SF and synovial tissue microbiome. A cross-sectional multi-disciplinary study was designed in the synovial fluid obtained from OA patients. 16S rRNA marker gene sequence analysis was performed to determine synovial fluid microbiome of 11 patients (8 females and 3 males) with knee pain and swelling due to OA underwent SF aspiration between April and July 2025. A total of 11 SF samples were analyzed. ITS2 amplification was negative in all samples, indicating the absence of detectable fungal signatures. In contrast, bacterial 16S rRNA gene was detected in six out of the 11 samples,