Abstract: BACKGROUND: The treatment for bacterial biofilms after internal fixation surgery is a very difficult problem in clinic. It is a great significance to establish an animal model of irrigation for treating bacterial biofilms in the early stage after internal fixation surgery.
OBJECTIVE: To establish an animal model for treating bacterial biofilms with different drugs through irrigation in early stage after internal fixation surgery.
METHODS: Six New Zealand white rabbits were selected. Bilateral femoral surfaces were exposed and drilled holes were made, and bone plates colonized with Pseudomonas aeruginosa (experimental group) and blank bone plates (blank control group) were implanted around the drilled holes on one side, and two drainage tubes were retained and fixed to serve as the “inlet” and “outlet,” respectively. The model was immersed for a certain period of time after simulated perfusion before rinsing. After the simulated irrigation, the plates were soaked for a certain time before washing. At 5 days postoperatively, the rabbits were observed for body temperature, wound condition, bacterial culture of drainage fluid, and crystalline violet staining and scanning electron microscopy of the bone plate.
RESULTS AND CONCLUSION: Six rabbits had difficulty in moving the affected limbs after surgery and showed elevated body temperature at 2-4 days after surgery. Local swelling could be touched at some wounds in the experimental group, and the wounds in the blank control group healed well. The results of bacterial culture of drainage fluid showed that Pseudomonas aeruginosa diffused or spread in the experimental group. At 5 days after surgery, the plate in the experimental group became purple shown by crystalline violet staining, and the absorbance value at 570 nm detected by the microplate reader was 2.621±0.088, indicating the presence of bacteria. Scanning electron microscopy at 5 days after surgery showed that a large number of bacterial microcolonies appeared on the surface of the plate in the experimental group, forming a highly inhomogeneous three-dimensional structure similar to the “mushroom-like” and “tower-like” structures, with filamentous water channels connecting the “mushroom-like” structures, which were typical biofilm structures with high densities, while no obvious colonies were seen in the blank control group. Overall, this animal model simulates the state of infected biofilm formation due to early infection after internal fixation and provides an available method of irrigation with different drugs.

Key words: bacterial biofilm, internal fixation, bone plate, animal model, infection, irrigation