Antimicrobial efficacy of on-label vs. hand-mixed irrigation solutions against S. aureus biofilms

Abstract

Wound irrigation is routinely performed as part of the DAIR procedure and for hardware infections, yet the most effective irrigation solution for reducing bacterial bioburden is unknown. Clinicians can choose on-label, commercially available irrigation solutions or hand-mix preparations off-label on the operating back table. Current methods for evaluating antiseptic efficacy often do not represent the clinical scenario. Here, we present a proof-of-concept ex vivo setup to evaluate whether on-label, commercially available irrigation solutions were superior at reducing bacterial biofilm burden compared to off-label, hand-mixed irrigation solutions. Staphylococcus aureus ATCC 49525 (Xen36) biofilms were grown on Grade 5 titanium simulated fracture fixation plates and secured to sections of autoclaved bovine femur with cortical bone screws. Fourteen irrigation solutions (three commercial, eleven hand-mixed) and one untreated control group were evaluated by irrigating the biofilm-ridden plates and quantifying the remaining bioburden using a 10-fold dilution series to determine the log₁₀ reduction. None of the fourteen treatments reduced bioburden statistically significantly compared to the untreated control, where no irrigation was performed. Additionally, no treatment achieved the FDA benchmark of a 4 log₁₀ reduction for antibacterial activity. An off-label, hand-mixed 0.472 % w/v chlorhexidine gluconate solution reduced the greatest bioburden overall, with a 1.43 ± 0.20 log₁₀ reduction. On-label irrigation products did not reduce bioburden more than off-label, hand-mixed solutions clinicians often prepare in the operating room. Musculoskeletal infections remain a significant clinical challenge and contribute to increasing healthcare costs. The antimicrobial efficacy of irrigation products should be assessed using clinically relevant models.