# Saponin Improves Recovery of Bacteria from Orthopaedic Implants for Enhanced Diagnosis Ex Vivo

## TL;DR

This study shows that saponin improves the recovery of bacteria from orthopedic implants, which could help in diagnosing joint infections more effectively.

## Contribution

The novel use of saponin as a biosurfactant to enhance bacterial recovery from orthopedic implants is introduced.

## Key findings

- Saponin treatment increased CFU recovery by up to 2.2 log10 for S. epidermidis compared to saline.
- A novel two-component kit with saponin and a transportation box is proposed for handling infected implants.
- Results were validated in a 3D PJI soft tissue in vitro model.

## Abstract

Biofilm formation on orthopedic joint implants complicates diagnosis of periprosthetic joint infections (PJIs). Sonication of explanted orthopedic implants for diagnostic enhances pathogen detection, but it shows limitations in sensitivity and handling. We investigated whether the biosurfactant saponin could improve bacterial recovery from orthopaedic implants and thereby enhance infection diagnosis ex vivo. 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, and Cutibacterium acnes were grown on the discs, which were then treated with either saline solution or various concentrations of saponin. Next, the discs were vortexed or sonicated. 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, and 0.01 log10 for E. coli. Furthermore, 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 suggest that biosurfactants can enhance bacterial recovery from artificially contaminated orthopedic implants, potentially improving the diagnosis of PJIs.