title: Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection.
abstract: BACKGROUND
  Periprosthetic joint infection (PJI) is a devastating complication following total joint arthroplasty. Current animal models of PJI are limited because of a lack of quantitative methods and failure to effectively recreate the periprosthetic space. We therefore developed a murine PJI model involving a 3-dimensionally printed Ti-6Al-4V implant capable of bearing weight and permitting quantitative analysis of periprosthetic bacterial load and evaluation of biofilm.
  
  
  METHODS
  Twenty-five 12-week-old C57BL/6 mice received a unilateral proximal tibial implant and intra-articular injection of either 3 × 10 colony forming units (CFUs) of Staphylococcus aureus Xen 36 or saline solution. Postoperatively, mice underwent gait analysis, knee radiographs, and serum inflammatory marker measurements. Following euthanasia at 2 or 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize biofilm.
  
  
  RESULTS
  All mice survived surgery and were not systemically septic. The control mice immediately tolerated weight-bearing and had normal inflammatory markers and radiographic signs of osseointegration. Infected mice had difficulty walking over time, exhibited radiographic findings of septic implant loosening, and had significantly elevated inflammatory markers. Periprosthetic tissues of the infected animals displayed a mean of 4.46 × 10 CFUs of S. aureus at 2 weeks and 2.53 × 10 CFUs at 6 weeks. Viable S. aureus was quantified on retrieved implant surfaces. SEM demonstrated S. aureus cocci in clusters encased within biofilm.
  
  
  CONCLUSIONS
  This animal model is, to our knowledge, the most clinically representative PJI replication to date. It is the first that we know of to produce infection through the same method hypothesized to occur clinically, utilize a weight-bearing implant that can osseointegrate, and provide quantitative data on 8 aspects of PJI, including radiographic features, inflammatory markers, and bacterial loads.
  
  
  CONCLUSIONS
  This novel animal model is, to our knowledge, the first to provide a load-bearing translational representation of clinical PJI that effectively recreates the periprosthetic space.
authors.affiliation: 1Hospital for Special Surgery, New York, NY 2University of Rochester, Rochester, New York.
authors.forename: Alberto V
authors.initials: AV
authors.lastname: Carli
authors.forename: Samrath
authors.initials: S
authors.lastname: Bhimani
authors.forename: Xu
authors.initials: X
authors.lastname: Yang
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Shirley
authors.forename: Karen L
authors.initials: KL
authors.lastname: de Mesy Bentley
authors.forename: F Patrick
authors.initials: FP
authors.lastname: Ross
authors.forename: Mathias P G
authors.initials: MP
authors.lastname: Bostrom
mesh_terms: D000818:Animals; D058491:Bacterial Load; D018441:Biofilms; D004195:Disease Models, Animal; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000382:microbiology*; D051379:Mice; D019736:Prostheses and Implants / Q000382:microbiology*; D016459:Prosthesis-Related Infections / Q000000981:diagnostic imaging / Q000382:microbiology*; D011859:Radiography; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000302:isolation & purification*