Antimicrobial effect of methylene blue in microbiologic culture to diagnose periprosthetic joint infection: an in vitro study

Abstract

Background: As one of the major diagnostic criteria in Musculoskeletal Infection Society, the microbiological diagnosis of periprosthetic joint infection (PJI) performed by analyzing periprosthetic tissue culture is recommended. The goal of this study was to determine if methylene blue (MB) has antibacterial effects that might interfere with microbial culture in vitro. Methods: Eight isolates of reference strains of Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Streptococcus pyogenes, and Candida albicans were incubated appropriately on blood agar, China blue agar, or Sabouraud’s agar plates at 35 ℃. (Streptococci were cultured in a CO2-rich atmosphere.) Each bacterial suspension was formed by 50-fold dilution before the test MB was added. For each strain, bacterial suspension was divided into 3 groups (5 samples each) exposed either MB 0.1%, MB 0.05% or sterile non-bacteriostatic 0.45% saline. The antimicrobial property of MB was determined by measuring the bacterial density on agar plates incubated for 24 h and comparing it with controls unexposed to MB. Results: Exposure to MB 0.1% or MB 0.05% negatively affected microbial viability in vitro. Of the diluted form of MB exposure, reference strains of S. hominis and A. baumannii resulted in fewer colony-forming units compared with the sterile saline control. MB concentration was significantly negatively correlated with CFU counts of S. hominis and A. baumannii strains. The antibacterial property of MB 0.1% or MB 0.05% appears to affect the ability to culture the organism in in vitro assays. Conclusion: MB 0.1% or MB 0.05% has strong antimicrobial activities against some commonly encountered bacterial strains in PJI in vitro. To further evaluate its potential antibacterial usefulness in clinical applications, the next studies are needed to assess the ability of MB to affect the ability to culture the pathogens in vivo, especially in periprosthetic tissue.