Bactericidal effects of diluted povidone-iodine on Staphylococcus epidermidis at different stages of biofilm formation on titanium surfaces

BACKGROUND: Implant-associated infections, particularly those caused by Staphylococcus epidermidis, pose a significant challenge in orthopaedic surgery due to the ability of this organism to form antibiotic-resistant biofilms on titanium surfaces. Although povidone-iodine (PVP-I) is widely used as an intraoperative antiseptic, its effectiveness against biofilms at different stages of development remains unclear. This in vitro study aimed to evaluate the bactericidal effects of 0.35% diluted PVP-I on S. epidermidis biofilms on mirror-polished titanium alloy (ASTM F136) discs. Irrigation with PVP-I or saline (control) was applied at three critical stages: (1) irrigation at the pre-exposure stage; (2) irrigation after the bacterial adhesion stage; and (3) irrigation at the early biofilm stage (6 h after adhesion). Viable bacterial counts were quantified by colony-forming unit (CFU) assays, and biofilm structure was assessed using biofilm coverage rate (BCR) measured by crystal violet staining and image analysis. RESULTS: Irrigation at the pre-exposure stage did not significantly reduce the number of adherent viable bacteria compared to controls (P = 0.55, d = 0.21). However, irrigation after the bacterial adhesion stage resulted in no viable bacteria being detected in the PVP-I group under the assay conditions (0 CFU/mL; P < 0.0001, d = 2.56). Irrigation at the early biofilm stage with PVP-I achieved a 98% reduction in viable bacteria compared to controls (P < 0.0001, d = 45.3). The relative BCR remained at 102.3% (P = 0.30, d = 0.24), likely due to matrix protein fixation by iodine rather than increased formation. CONCLUSIONS: The timing of antiseptic irrigation is critical for effective reduction of viable bacteria from titanium surfaces. Irrigation after the bacterial adhesion stage with diluted PVP-I appears most effective in preventing biofilm establishment, while irrigation at the pre-exposure stage is insufficient, and chemical irrigation alone cannot fully remove established biofilm matrix structures. These findings highlight the importance of integrating mechanical debridement with antiseptic irrigation for optimal management of implant-associated infections.