Efficacy of dalbavancin against MRSA biofilms in a rat model of orthopaedic implant-associated infection

Objectives: The aim of this study was to evaluate the efficacy of dalbavancin against MRSA biofilm-related infection in orthopaedic implants in vivo. Methods: One MRSA strain isolated from human osteomyelitis was used to promote biofilm formation on the surface of screws. The implants were inserted in the proximal tibia under general anaesthesia. Thirty-nine Wistar rats were divided into three groups [control group (no treatment), Group 1 (7 days of treatment) and Group 2 (14 days of treatment)]; both treatment groups were administered dalbavancin intraperitoneally and euthanized after treatment. cfu of bacteria present in both the tibia and the implant were quantified. The infection severity was assessed by histopathology and scored from 0 (no infection) to 4 (severe infection). Results: The high number of cfu/g and cfu/mL present in the control group indicated a well-established infection. There was a significant reduction in cfu in rats treated with dalbavancin both in the tibia (2.8x10(5) cfu/g) and the implant (1.1x10(6) cfu/mL) in Group 1 (1.8x10(3) cfu/g and 2.4x10(5) cfu/mL, respectively) and in Group 2 (8.2 cfu/g and 8.2x10(3) cfu/mL, respectively). Most animals from the control group presented an infection scored as 3 (severe). At the end of the experiment, most rats from Groups 1 and 2 presented an infection scored as 2 (moderate) and 0 (no infection), respectively. Conclusions: Although there was a marked decrease in cfu number, signs of biofilm-induced infection prevailed after 14 days of treatment. Further studies should be carried out to evaluate the potential of dalbavancin in the treatment of bone and orthopaedic implant-associated MRSA infections.