A Unique Mouse Model for Quantitative Assessment of Biofilm Formation on Surgical Implants in Subcutaneous Abscess

To develop a novel biomaterial with antibacterial properties for orthopedic surgical procedures, establishing an experimental animal model of implant-related infections that closely mimics the pathological state is crucial. Additionally, a quantitative comparison with control samples is required to assess biofilm formation on materials. However, current animal models, which involve implanting each individual with a single material, may yield inconsistent outcomes due to the heterogeneity of infection status among subjects. Furthermore, accurately quantifying biofilm formation on materials in vivo remains challenging, and the findings may lack reliability. To address these issues, this study demonstrated a unique mouse model of implant-related infection that enables the simultaneous incubation of two implants with bacteria in an enclosed environment within a single mouse, forming an encapsulated subcutaneous abscess. A mature air pouch was initially created beneath the skin of the back. Two stainless steel wires were connected and placed into the pouch, followed by the inoculation of Xen 36, a bioluminescent strain of Staphylococcus aureus. By 14 days after inoculation, a subcutaneous abscess had formed around the wires. The biofilm was completely removed from the surface of each wire, and the dissolved bacterial suspensions were accurately measured using optimized methods to assess biofilm formation on the implant, determine colony-forming units, and perform quantitative polymerase chain reaction analysis. By leveraging the lux operon of the bioluminescent bacteria, the relative expression levels of luxA and 16S rRNA were used to determine the bacterial load within the biofilm on each wire. This optimized comparative analytical approach enables precise assessments of biofilm formation on two wires under uniform infection conditions within a single mouse model and may facilitate the advancement of biomaterials with antibacterial properties.