In Vivo Bioluminescence Imaging in a Rabbit Model of Orthopaedic Implant-Associated Infection to Monitor Efficacy of an Antibiotic-Releasing Coating

Abstract

Background: In vivo bioluminescence imaging (BLI) provides noninvasive monitoring of bacterial burden in animal models of orthopaedic implant-associated infection (OIAI). However, technical limitations have limited its use to mouse and rat models of OIAI. The goal of this study was to develop a larger, rabbit model of OIAI using in vivo BLI to evaluate the efficacy of an antibiotic-releasing implant coating. Methods: A nanofiber coating loaded with or without linezolid-rifampin was electrospun onto a surgical-grade locking peg. To model OIAI in rabbits, a medial parapatellar arthrotomy was performed to ream the femoral canal, and a bright bioluminescent methicillin-resistant Staphylococcus aureus (MRSA) strain was inoculated into the canal, followed by retrograde insertion of the coated implant flush with the articular surface. In vivo BLI signals were confirmed by ex vivo colony-forming units (CFUs) from tissue, bone, and implant specimens. Results: In this rabbit model of OIAI (n = 6 rabbits per group), implants coated without antibiotics were associated with significantly increased knee width and in vivo BLI signals compared with implants coated with linezolid-rifampin (p < 0.001 and p < 0.05, respectively). On day 7, the implants without antibiotics were associated with significantly increased CFUs from tissue (mean [and standard error of the mean], 1.4 • 10 8 ± 2.1 • 10 7 CFUs; p < 0.001), bone (6.9 • 10 6 ± 3.1 • 10 6 CFUs; p < 0.05), and implant (5.1 • 10 5 ± 2.2 • 10 5 CFUs; p < 0.05) specimens compared with implants with linezolidrifampin, which demonstrated no detectable CFUs from any source. Conclusions: By combining a bright bioluminescent MRSA strain with modified techniques, in vivo BLI in a rabbit model of OIAI demonstrated the efficacy of an antibiotic-releasing coating. Clinical Relevance: The new capability of in vivo BLI for noninvasive monitoring of bacterial burden in larger-animal models of OIAI may have important preclinical relevance.

Preclinical Optical Imaging to Study Pathogenesis, Novel Therapeutics and Diagnostics Against Orthopaedic Infection

“…Moreover, using a near‐infrared fluorescent dye as a surrogate for antibiotic release from the coating, in vivo FLI imaging was employed to quantify and determine the duration of release of the fluorescent dye from the coating . Of note, the coating with combinatorial linezolid and rifampin release also prevented an MRSA (SAP231) infection in our rabbit model of OIAI . Similarly, Stavrakis et al used in vivo BLI in the K‐wire mouse model of OIAI with an implant coating composed of poly(ethylene glycol)‐poly(propylene sulfide) that released either vancomycin or tigecycline.…”

“…Finally, the use of in vivo optical imaging has been expanded beyond mouse and rat models of OIAI to study the pathogenesis of OIAI in larger animals, which better simulate the surgical procedures and larger implants used in orthopaedic surgeries in humans. For example, our lab developed a rabbit model of OIAI in which a bright MRSA bioluminescent strain (SAP231) was inoculated onto an orthopaedic‐grade locking peg that was inserted retrograde into the distal femurs of rabbits . In this rabbit model of OIAI, we were able to successfully use in vivo BLI imaging to monitor the bacterial infection by taking advantage of the increased brightness of strain SAP231 that allowed deeper tissue penetration of the in vivo BLI signals in conjunction with the use of Dutch‐Belted rabbits in which the adults were small enough to fit within the chamber of a commercial IVIS Lumina III (PerkinElmer) …”

“…For example, our lab developed a rabbit model of OIAI in which a bright MRSA bioluminescent strain (SAP231 13 ) was inoculated onto an orthopaedic-grade locking peg that was inserted retrograde into the distal femurs of rabbits. 35 In this rabbit model of OIAI, we were able to successfully use in vivo BLI imaging to monitor the bacterial infection by taking advantage of the increased brightness of strain SAP231 that allowed deeper tissue penetration of the in vivo BLI signals in conjunction with the use of Dutch-Belted rabbits in which the adults were small enough to fit within the chamber of a commercial IVIS Lumina III (PerkinElmer). 35 It should be mentioned that in vivo BLI could be used in conjunction with bioluminescent parental and isogenic deletion mutant bacterial strains that lack specific virulence factors to provide novel insights into the role of bacterial virulence factors in the pathogenesis of OIAI.…”

“…35 In this rabbit model of OIAI, we were able to successfully use in vivo BLI imaging to monitor the bacterial infection by taking advantage of the increased brightness of strain SAP231 that allowed deeper tissue penetration of the in vivo BLI signals in conjunction with the use of Dutch-Belted rabbits in which the adults were small enough to fit within the chamber of a commercial IVIS Lumina III (PerkinElmer). 35 It should be mentioned that in vivo BLI could be used in conjunction with bioluminescent parental and isogenic deletion mutant bacterial strains that lack specific virulence factors to provide novel insights into the role of bacterial virulence factors in the pathogenesis of OIAI. In other S. aureus infection models, prior studies have used in vivo BLI with bioluminescent parental and isogenic agr or clumping factor B (ClfB) deletion mutant strains during a S. aureus skin infection in mice and a bioluminescent parental and an isogenic LukAB deletion mutant strain during a S. aureus bacteremia/kidney abscess infection in mice.…”

“…47 Of note, the coating with combinatorial linezolid and rifampin release also prevented an MRSA (SAP231) infection in our rabbit model of OIAI. 35 Similarly, Stavrakis et al 48 used in vivo BLI in the K-wire mouse model of OIAI with an implant coating composed of poly(ethylene glycol)-poly(propylene sulfide) that released either vancomycin or tigecycline. They reported that the local release from the coating of tigecycline was more effective than vancomycin in reducing the bacterial burden.…”