Predictors of Implant Failure in Orthopaedic Infections Due to Coagulase-Negative Staphylococci: The Impact of Biofilm and Proteolytic Enzymes – A Prospective Observational Study.

Background: Coagulase-negative staphylococci (CoNS), long considered low-virulence skin commensals, have emerged as significant pathogens in orthopaedic implant-associated infections. Their ability to form biofilms and produce proteolytic enzymes contributes to chronic infection, antimicrobial resistance, and implant failure. Objectives: To evaluate the microbiological and biochemical characteristics of CoNS isolates from orthopaedic implant infections, assess antimicrobial susceptibility, and identify predictors of adverse clinical outcomes, including implant removal and delayed bone healing. Methods: This prospective observational study enrolled 120 patients with suspected implant-associated infections over two years. Sonication fluid and periprosthetic tissue cultures were performed, and isolates underwent species identification, antimicrobial susceptibility testing, and assessment of biofilm formation, exopolysaccharide production, and protease activity. Clinical outcomes were recorded over a six-month follow-up. Statistical analyses included multivariate logistic regression and correlation studies. Results: CoNS were isolated in 48 cases (40%), predominantly Staphylococcus epidermidis (70.8%). Methicillin resistance was present in 68.7% of isolates, with high rates of multidrug resistance to erythromycin (79.1%), ciprofloxacin (64.5%), and clindamycin (60.4%). Strong biofilm production was observed in 79.1% of isolates and was significantly associated with implant removal (73.6% vs. 30%; p=0.004), prolonged antibiotic therapy (mean 6.4 vs. 4.2 weeks; p=0.001), and delayed union (44.7% vs. 20%; p=0.03). Multivariate analysis identified strong biofilm production (OR 4.25; p=0.015) and higher proteolytic enzyme activity (OR 1.92; p=0.040) as independent predictors of implant removal. Conclusions: CoNS are major contributors to orthopaedic implant failure, primarily driven by biofilm-related virulence and proteolytic activity rather than methicillin resistance alone. These findings highlight the need for early microbiological diagnosis and biofilm-targeted interventions. Recommendations: Clinicians should incorporate implant sonication and biofilm assessment into routine diagnostic protocols and consider prolonged antimicrobial therapy and early surgical intervention in cases with strong biofilm-producing CoNS. Future research should focus on molecular characterization of virulence factors and anti-biofilm therapies to improve treatment outcomes