Staphylococcus epidermidis is one of the most common causative agents of periprosthetic joint infections, where effective diagnostics are often challenging. Most recent studies focus primarily on biochemical markers, while physicochemical markers, such as synovial fluid viscosity, remain insufficiently explored. The aim of our study was to investigate: (i) whether S. epidermidis can successfully grow in synovial fluid, (ii) whether the presence of extracellular hyaluronidases, which could potentially affect viscosity, can be detected using an enzymatic assay, (iii) whether bacterial presence influences the reduction of synovial fluid viscosity under in vitro conditions, and (iv) whether clinical isolates of S. epidermidis can form biofilms under in vitro conditions. We used five different clinical isolates and the reference laboratory strain ATCC12228. By measuring OD₆₀₀ before and after inoculation into synovial fluid, we confirmed that all strains were able to grow successfully. Hyaluronidase activity was assessed using an enzymatic assay, where the formation of complexes between intact hyaluronic acid and albumin was monitored via OD₆₀₀ measurements. Under the given conditions, no hyaluronidase activity was detected. Viscosity measurements were performed using a concentric cylinder viscometer after exposing synovial fluid to bacterial biofilms and supernatants of the tested strains. Measurements were conducted at different shear rates. The results showed that the presence of S. epidermidis did not affect the viscosity of synovial fluid under the tested conditions. Based on these findings, we can conclude that S. epidermidis does not influence the viscosity of synovial fluid under the in vitro conditions tested.
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