Presence of bacterial DNA in synovial fluid from the temporomandibular joint in patients with temporomandibular joint disorders

<h4>Introduction</h4>Temporomandibular joint disorders (TMJD) are common, affecting approximately 30% of the population. While the aetiology of TMJD has been considerably discussed, one aspect that has not been thoroughly investigated is the potential occurrence and role of bacteria in the temporomandibular joint (TMJ). This study aimed to determine the existence of bacteria in the TMJ synovial fluid of patients with TMJD.<h4>Methods</h4>In this cohort study, synovial fluid from patients with TMJD, was collected during routine surgery at the Oral and Maxillofacial Unit at Karolinska University Hospital, Stockholm. Data analysis of the bacterial 16S rRNA sequencing was performed using automated cloud-based EPI2ME workflows (Oxford Nanopore Technologies).<h4>Results</h4>The synovial fluid of 64 patients (mean age 41 years), of whom 86% (<i>n</i> = 55) were women, was analysed, and bacterial rRNA were detected in 64% (<i>n</i> = 41). Most commonly, one bacterial genus was detected in each patient (<i>n</i> = 19), two bacteria were detected in twelve patients, three in four patients, four in five patients and one patient had six different bacterial genera in its TMJ synovial fluid. The most common bacterial genera found were <i>Staphylococcus</i> (<i>n</i> = 8), <i>Streptococcus</i> (<i>n</i> = 7), <i>Cutibacterium</i> (<i>n</i> = 4), and <i>Peptoniphilus</i> and <i>Moraxella</i> (<i>n</i> = 3). The origin of these bacteria suggests two main dissemination routes to the TMJ: hematogenous spread and contamination during previous handling of sample.<h4>Conclusion</h4>The findings of this study indicate that bacterial presence within the TMJ seems frequent and demonstrates diagnostic clustering, that warrant further investigation. However, the results should be interpreted with caution because of the high sensitivity of 16S rRNA sequencing.