Optimization of a fracture-related infection (FRI) rat model to mimic bacterial contaminated open fractures in orthopaedic patients - a model development study.

Abstract

Open fractures are at risk for fracture-related infection (FRI) due to environmental contamination, with 40-80% of bacteria existing in biofilms. Standard treatment includes prophylactic antibiotics, surgical debridement, and irrigation; however, bacteria can persist in a biofilm/sessile form on bones and orthopedic implants. While some infections show clear clinical symptoms, others may remain subclinical for long periods. These biofilm-associated infections are difficult to treat due to their reduced susceptibility to antibiotics. This study aims to develop a clinically relevant rat model for FRI, overcoming limitations of existing models that use non-clinical materials like Polyetheretherketone (PEEK) and planktonic bacteria. By inoculating the fracture site with bacteria isolated from biofilms and utilizing stainless steel surgical implants, which are standard in clinical practice, we aim to create a more accurate representation of FRI. This improved model will provide a valuable tool for preclinical research for improving the management of FRIs, enabling the evaluation of therapeutic interventions on biofilm infections in the presence of clinically relevant implants. The experimental procedure involved creating a femur fracture in an anesthetized rat and inoculating it with 10-10CFUs/ml Staphylococcus aureus bacteria derived from biofilms grown in vitro on glass slides for three days. The fracture was stabilized with a stainless-steel plate and screws, and the wound was closed. After one week, the anesthetized rats underwent surgical debridement and irrigation and received one dose of systemic antibiotic cefazolin. Three weeks after fracture, rats were euthanized, and the hardware and bone were harvested, washed of planktonic bacteria, and separately analyzed for CFUs. The results showed the rats demonstrated S. aureus biofilm growth in the bone and hardware with > 10CFUs/ml. There were no differences between CFUs/ml in bone and on hardware. Our FRI model is uniquely valuable as a model for evaluating novel therapeutics against implant-associated infections.