Bacterial DNA in joint tissue and its role in osteoarthritis: a narrative review

Osteoarthritis (OA) is a complex condition that involves immunological, metabolic, and inflammatory processes, as well as mechanical deterioration. Even in the absence of overt infection, recent developments in molecular diagnostics have revealed that synovial fluid, synovial tissue, and articular cartilage from patients with OA contain bacterial DNA and other microbial components. These results cast doubt on the conventional theory of joint sterility and raise the possibility that the gut–joint axis plays a role in disease etiology. In accordance with the PRISMA-style methodology, this narrative review summarizes the most recent human data on microbial DNA detection in joint tissues, investigates mechanisms of innate immune activation and microbial translocation, and assesses their clinical implications. Microbial markers in OA joints differ from those in healthy controls. They are associated with inflammatory mediators such as lipopolysaccharide (LPS), according to observational, cross-sectional, and emerging interventional studies. Toll-like receptor (TLR)-mediated pathways may be activated by microbial components, leading to cartilage degradation and synovitis. Causality remains unknown despite encouraging results due to methodological flaws and potential contamination biases. Gaining insight into the role of microbes in OA could lead to the development of new biomarkers and treatments targeting the microbiome.