María Guembe ^1* Nils Hailer ² Pablo Sanz-Ruiz ¹

• ¹ Gregorio Marañón Hospital, Madrid, Spain
• ² Uppsala University Hospital, Uppsala, Uppsala, Sweden

Prosthetic Joint Infection (PJI) is an important healthcare problem which affects 1-2% of patients undergoing prosthetic surgery, having become the most common reason for early revisions after knee arthroplasty and the second most common reason after hip arthroplasty. PJI causes enormous suffering, it is associated with a mortality being higher than in some cancer, such as prostate or breast malignancies, and costs for healthcare often exceed 100,000 € per affected patient. The main causative and differentiating factor related to PJI is microorganisms' ability to form a biofilm, which confers high resistance to antibiotics and to host immune response. Thus, this implies a difficulty in combating it, the ineffectiveness of many antibiotics and, in most cases, the need for prosthesis exchange. Despite recent advances in prevention and treatment, there is still an urgent need to enhance our basic understanding of the pathophysiology and to improve clinical success rates. Different surgical treatments have been proposed, such as radical debridement, one or two stage or even resection arthroplasty, combined with different antibiotic protocols (short duration, long duration, suppression treatment…). Recent studies show success rates of around 70% with current treatment strategies. In the current Research Topic, 6 original articles, including perspectives and revisions, have been published towards new approaches in diagnosis and treatment of PJI.Bogut et al. undertake the genomic characterization of a SCV strain of Staphylococcus epidermidis derived from a patient with a late PJI. The authors hypothesize that multiple deletions, amongst them the absence of the Staphylococcal cassette chromosome, may contribute to switching of this bacteria's phenotype to a SCV, and to streamlining the genetic content towards adaptation to chronicity. Interestingly, in the reported strain, some single nucleotide polymorphisms found in genes related to virulence factors and biofilm formation may also be associated with the development of SCV. Surely, in the near future, genomic analysis of bacteria isolated from PJI patients will help physicians understand the virulence, resistance patterns and the propensity to form biofilm. This will enable improved, personalized antibiotic regimes and facilitate the choice between more conservative, implant-preserving and more aggressive surgical strategies. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1289844/full. The diagnosis of PJI remains challenging, and numerous approaches to increase the accuracy of analyses of joint fluid aspirates have been undertaken. In the paper by Maritati et al., the activity of the leukocyte-derived enzyme myeloperoxidase is measured in such aspirates from patients with or without PJI, and the diagnostic accuracy is evaluated and compared to the established leukocyte-esterase assay. By calculating an area under the curve (AUC) of 0.86 and a cut-off value discriminating between infected and non-infected patients, the authors find good diagnostic accuracy and propose that the assay be validated in larger samples. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1417049/full.In the effort to improve diagnosis through synovial fluid aspiration, Morovic et al. analyze the presence of D-lactate and L-lactate as potential biomarkers for PJI. This approach is based on the fact that bacteria and fungi are uniquely capable of producing both forms of lactate, whereas human cells can only produce the L-lactate isoform. To test this hypothesis, they analyzed Dlactate and L-lactate concentrations in cultures of the main bacteria responsible for PJI. They observed that all bacterial strains produced D-lactate (regardless of whether they were in planktonic or biofilm form), unlike L-lactate, which was only produced by certain strains.Consequently, they recommend D-lactate as a more reliable biomarker than L-lactate.