Disclosing Agents for the Intraoperative Identification of Biofilms on Orthopedic Implants

Disclosing agents are dyes used in dentistry to colorize plaque (biofilm) and may offer a means for intraoperative detection of biofilms on orthopedic implants. Methylene blue (MB) stains biofilm and is safely used in orthopedic applications. Injection of MB into acutely infected prosthetic knees before debridement may enable visualization of biofilm, which could influence treatment decisions. The aims of this study were to determine if MB could be used to visualize biofilm on total knee arthroplasty (TKA) implants and to determine if MB staining has an antimicrobial effect that might interfere with subsequent culture.

Staphylococcus epidermidis biofilms were formed on TKA polyethylene liners and polymethylmethacrylate (PMMA) and Teflon discs. After staining biofilms on these implants, the bacterial densities were determined through sonication and quantitative culture. The antimicrobial activity of MB staining was determined by measuring the bacterial density of S. epidermidis biofilms on PMMA discs incubated in 0.05% MB for 24 hours vs 30 seconds and comparing it with controls unexposed to MB.

MB stained S. epidermidis biofilms grown on TKA implants and Teflon and PMMA discs in vitro. Sonication and quantitative culture of the stained implants showed that bacterial densities were at supraphysiological levels. Staining did not affect the ability to culture the organism.

MB is a possible cost-effective and novel method to expeditiously identify intraoperative biofilm. To further evaluate MB staining and its potential clinical usefulness, future studies are needed to assess the ability of MB to stain physiological levels of biofilm.