Plate-associated localized osteitis in mini-pig by biofilm-forming Methicillin-resistant Staphylococcus aureus (MRSA): establishment of a novel experimental model

Abstract

Purpose The increasing number of implant-associated infections during trauma and orthopedic surgery caused by biofilm-forming Staphylococcus aureus in combination with an increasing resistance of conventional antibiotics requires new therapeutic strategies. One possibility could be testing for different therapeutic strategies with differently coated plates. Therefore, a clinically realistic model is required. The pig offers the best comparability to the human situation, thus it was chosen for this model. The present study characterizes a novel model of a standardized low-grade acute osteitis with bone defect in the femur in mini-pigs, which is stabilized by a titanium locking plate to enable further studies with various coatings. Methods A bone defect was performed on the femur of 7 Aachen mini-pigs and infected with Methicillin-resistant S. aureus (MRSA ATCC 33592). The defect zone was stabilized with a titanium plate. After 14 days, a plate change, wound debridement and lavage were performed. Finally, after 42 days, the animals were lavaged and debrided again, followed by euthanasia. The fracture healing was evaluated radiologically and histologically. Results A local osteitis with radiologically visible lysis of the bone could be established. The unchanged high Colony-forming Units (CFU) in lavage, the significant differences in Interleukin (IL)-6 in blood compared to lavage and the lack of increase in Alkaline Phosphates (ALP) in serum over the entire observation period show the constant local infection. Conclusion The study shows the successful induction of local osteitis with lysis of the bone and the lack of enzymatic activity to mineralize the bone. Therefore, this standardized mini-pig model can be used in further clinical studies, to investigate various coated implants, bone healing, biofilm formation and immune response in implant-associated osteitis.

Efficacy of lysostaphin-coated titanium plates on implant-associated MRSA osteitis in minipigs

“…All surgeries were performed under aseptic conditions in the operating rooms of our local animal facility according to the standardized infection model previously established by our research group [ 24 ]. For premedication, we used ketamine 10 mg/kg i.m., azaperone 5 mg/kg i.m., diazepam 10–20 mg i.m., and atropine 0.5 mg i.m.…”

“…Examinations in large animal models (e.g., pig or sheep) are pending but are urgently needed to approach the clinical practice and pave the way for future human clinical trials. The most recent study of our working group shows the successful establishment of an IAI by methicillin-resistant Staphylococcus aureus (MRSA) in minipigs [ 24 ]. This was deliberately developed as a fundamental for investigating further therapeutic strategies in IAIs.…”

Choosing the right animal model for osteomyelitis research: Considerations and challenges

“…In this model, medial tibial tubercle and crest received an injection of 10 μL sterile 0.9 % isotonic saline containing 10 2 –10 4 CFU of a porcine S. aureus strain (S54F9 spa-type t1333) before insertion of stainless-steel implants and the pigs were observed for 15 consecutive days. Miniature pigs were also selected to establish IAO [ 165 ]. A standardized bone defect of 2.8 × 5 mm was created in the midshaft of the femur and covered with a titanium plate infected with 1 × 10 5 CFU of ATCC MRSA 33592.…”

Efficacy of lysostaphin-coated titanium plates on implant- associated MRSA osteitis in minipigs

“…All surgeries were performed under aseptic conditions in the operating rooms of our local animal facility according to the standardized infection model previously established by our research group [24]. For premedication we used ketamine 10 mg/kg i.m., azaperone 5 mg/kg i.m., diazepam 10-20 mg i.m.…”