Saponin Improves Detachment and Recovery of Bacteria from Orthopaedic Implants—An In Vitro Study

Biofilm formation on orthopedic joint implants complicates treatment and diagnosis of periprosthetic joint infections (PJIs). Sonication of explanted orthopedic implants enhances pathogen detection, but it shows limitations in sensitivity and handling. We investigated whether the biosurfactant saponin could improve bacterial recovery from explanted implants. Orthopaedic material discs of 1 cm diameter were contaminated with different clinical bacterial PJI isolates. Biofilms of Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Cutibacterium avidum, Cutibacterium acnes, and Cutibacterium granulosum were grown on the discs, which were then treated with either saline solution or various concentrations of saponin. Next, disks were vortexed or sonicated. prior to vortexing or sonication. Colony forming units (CFUs) enumeration and time-to-positivity of liquid cultures were determined. Additionally, a novel 3D PJI soft-tissue in vitro model was established to validate these findings in a more representative scenario. Median CFU enumeration showed that 0.001% (w/v) saponin as compared to saline solution increased CFUs recovery by 2.2 log10 for S. epidermidis, 0.6 log10 for S. aureus, 0.6 log10 for C. avidum, 1.1 log10 for C. acnes, 0.7 log10 for C. granulosum, and 0.01 log10 for E. coli. Further, saponin treatment resulted in a >1 log10 increase in S. epidermidis CFU recovery from implants in the 3D tissue model compared to standard saline sonication. With that, we propose a novel two-component kit, consisting of a saponin solution and a specialized transportation box, for the efficient collection, transportation, and processing of potentially infected implants. Our data suggests that biosurfactants can enhance bacterial recovery from artificially contaminated orthopedic implants, potentially improving the diagnosis of PJIs.