Rifampin monotherapy was compared to the combination of
linezolid or
vancomycin with
rifampin in an experimental rat model of methicillin-resistant Staphylococcus aureus (MRSA) chronic
foreign body osteomyelitis. MRSA was inoculated into the proximal tibia, and a
titanium wire was implanted. Four weeks after
infection, rats were treated intraperitoneally for 21 days with
rifampin alone (n = 16),
linezolid plus
rifampin (n = 14), or
vancomycin plus
rifampin (n = 13). Thirteen animals received no treatment. At completion of treatment, qualitative cultures of the wire and quantitative cultures of the bone (reported as median values) were performed. Quantitative cultures from the control,
rifampin monotherapy,
linezolid-plus-
rifampin, and
vancomycin-plus-
rifampin groups revealed 4.54, 0.71, 0.10, and 0.50 log₁₀ CFU/gram of bone, respectively. The bacterial load was significantly reduced in all treatment groups compared to that in the control group.
Rifampin resistance was detected in isolates from 10, 2, and 1 animal in the
rifampin,
linezolid-plus-
rifampin, and
vancomycin-plus-
rifampin groups, respectively. Cultures of the removed wire revealed bacterial growth in 1 and 2 animals in the
rifampin and
linezolid-plus-
rifampin groups, respectively, with no growth in the
vancomycin-plus-
rifampin group and growth from all wires in the untreated group. In conclusion, we demonstrated that combination treatment with
linezolid plus
rifampin or
vancomycin plus
rifampin is effective in an animal model of MRSA
foreign body osteomyelitis in the context of retention of the infected
foreign body.