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Orthopaedic Proceedings
Vol. 105-B, Issue SUPP_17 | Pages 21 - 21
24 Nov 2023
RETHINKING THE INOCULUM USED IN ANIMAL MODELS OF IMPLANT-ASSOCIATED OSTEOMYELITIS: THE FORMATION AND APPLICATION OF BACTERIAL AGGREGATES
Hartmann KT Nielsen RL Mikkelsen F Ingmer H Kvich LA Aalbaek B Odgaard A Jensen HE Lichtenberg M Bjarnsholt T Jensen LK
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Aim

To make an inoculum for induction of Implant-Associated Osteomyelitis (IAO) in pigs based on bacterial aggregates resembling those found on the human skin, i.e. aggregates of 5–15 µm with low metabolic activity. The aggregates were evaluated and compared to a standard planktonic bacterial inoculum.

Method

The porcine Staphylococcus aureus strain S54F9 was cultured in Tryptone Soya Broth for seven days. Subsequently, the culture was filtered through cell strainers with pore sizes of 15 µm and 5 µm, respectively. The fraction of 5–15 µm aggregates in the top of the 5 µm filter was collected as the aggregate-inoculum. The separation of aggregates into different size fractions was evaluated by light microscopy. The metabolism of the aggregate-inoculum and a standard overnight planktonic inoculum was evaluated with isothermal microcalorimetry. In total, six female minipigs were allocated into three groups (n=2), receiving different inoculums. Group A: overnight planktonic inoculum; 104 CFU S. aureus (S54F9), Group B: seven days old 5–15 µm aggregate-inoculum; 104 CFU S. aureus (S54F9), Group C: saline. All inoculums were placed in a pre-drilled implant cavity in the right tibia of the pig and a sterile stainless-steel implant was inserted. The pigs were euthanized seven days after surgery. Postmortem macroscopic pathology, microbiology, computed tomography and histopathology were performed.

Orthopaedic Proceedings
Vol. 104-B, Issue SUPP_10 | Pages 30 - 30
1 Oct 2022
NEW INORGANIC/ORGANIC NANO-STRUCTURED XEROGEL COATING PREVENTS DEVELOPMENT OF OSTEOMYELITIS IN A PORCINE MODEL
Jensen LK Jensen HE Blirup SA Bue M Hanberg P Soto S Aalbaek B Arkas M Vardavoulias M
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Aim

To develop a new system for antibacterial coating of joint prosthesis and osteosynthesis material. The new coating system was designed to release gentamicin immediately after insertion to eradicate surgical contamination.

Method

Steel implants (2×15mm) were coated with a solid nanocomposite xerogel made from silica and the dendritic polymer, hyperbranched polyethyleneimine. The xerogel was anchored inside a porous surface made by pre-coating with titanium microspheres. Finally, gentamicin was encapsulated in the xerogel, i.e. no chemical binding. A total of 50 µg gentamicin was captured into each implant. The efficacy of the new coating was evaluated in a porcine model of implant associated osteomyelitis. In total, 30 female pigs were randomized into 3 study groups (n=10). Group A; plain implants + saline, Group B; plain implants + 104 CFU of Staphylococcus aureus, and Group C; coated implants + 104 CFU of S. aureus. Implant + inoculum was placed into a pre-drilled implant cavity of the right tibia and the pig was euthanized 5 days afterwards. Postmortem microbiology and pathology were performed. Two additional pigs were used in a pharmacokinetic study where microdialysis (MD) catheters were placed alongside coated implants. Extracellular fluid was sampled regularly for 24 hours from the MD catheters and analyzed for gentamicin content.