ANALYSIS OF SUSPENDED BIOFILM IN JOINT FLUIDS FROM PERIPROSTHETIC STAPHYLOCOCCAL INFECTIONS

Aim Periprosthetic infection (PPI) continues to be a problem in orthopedic surgery with a frequency of around 3%-5% and the main causative etiology is Staphylococcus spp. Once infection is established, the ability of multiple bacteria and fungi to generate biofilm on the prosthesis and surrounding tissues makes it difficult to eradicate the infection due to their ability to resist antibiotics and the immune response, which is a challenge in clinical practice. The ability of Staphylococcus spp. to form suspended aggregates on fluids, and not on surfaces, has recently been described (1-5). Therefore, in our study we aim to explore the frequency of this phenomenon of Staphylococcal “biofilm-like” suspended aggregates in joint fluid samples. Method During 1 year patients suspected of knee and hip PPI and who have signed the informed consent form prior to surgery were enrolled and joint fluids were cultured. In case of positivity with isolation of Staphylococci we tested bacterial aggregation by inoculating a 24h-mature biofilm suspension of each strain with 50% fetal bovine serum followed by an incubation of 1h at 22ºC under orbital shaking to observe the macroscopic formation of floating aggregates. We classify aggregation production from 1 to 5. We also quantify biomass and metabolic activity of the biofilm by crystal violet and XTT staining techniques, respectively. Clinical-microbiological data were also collected and patients were classified based on the Philadelphia consensus criteria 2018 into proven PPI (a major criterion or >6 points in minor criteria), possible PPI (2-5 points in minor criteria) or unlikely PPI (<2 points). Results We included 11 positive cultures from 10 patients (5 with Staphylococcus aureus and 6 with coagulase-negative Staphylococci). Floating aggregates were formed in 63.6% of the strains, being most of them of grade 2. We did not find statistically significant differences in the level of aggregates’ production according to species. We also observed that CoNS showed higher biomass production. All PPI were proven and 27.3% occurred at an early stage (≥1 month) being these not associated to aggregates’ production (p=0.721). Conclusions We observed that staphylococcal biofilm floating aggregates commonly occurred in strains from joint fluids, being mainly of low intensity. It is needed to further assess its role in the pathogenesis of PPI.