A new experimental model of acute osteomyelitis due to methicillin-resistant Staphylococcus aureus in rabbit

Aims: To assess the impact of antibiotic therapy on severe osseous infections, animal models of chronic bacterial infections have been developed; however, these models suffer from many experimental limitations. The aim of this work was to develop a new model system in which high levels of bacteria are obtained within femoral bone marrow and bone tissue, and such infections are maintained for at least 14 days. Methods and Results: Experimental osteomyelitis was induced in 25 New Zealand white rabbits. A 109 CFU ml-1 suspension of methicillin-resistant Staphylococcus aureus was injected into the knee after bone trepanation. On day 3, surgical debridement was performed to mimic a surgical procedure. Animals were euthanized 1, 2, 3, 9 and 14 days post-inoculation to determine the bacterial counts in marrow and bone, and to evaluate the stability of the infection. Inoculated lesions also were assessed for changes in histological parameters on days 3 and 7 post-inoculation. At days 1, 2, 3, 9 and 14 post-inoculation, we observed 6 center dot 50 +/- 0 center dot 64, 7 center dot 30 +/- 0 center dot 49, 7 center dot 82 +/- 0 center dot 19, 8 center dot 00 +/- 1 center dot 48 and 8 center dot 99 +/- 0 center dot 20 log10 CFU g-1 in bone marrow and 8 center dot 40 +/- 0 center dot 68, 7 center dot 65 +/- 0 center dot 27, 7 center dot 58 +/- 0 center dot 30, 8 center dot 88 +/- 0 center dot 52 and 8 center dot 28 +/- 0 center dot 39 log10 CFU g-1 in bone tissue, respectively. No statistical differences in bacterial count were found between bone marrow and bone tissue at any time point. Conclusion: This new model of acute osteomyelitis was validated by histological and microbiological changes in the absence of sclerosing agents, and these changes remained stable for 14 days. Significance and Impact of the Study: These results describe a new experimental model of acute osteomyelitis and demonstrate its usefulness in assessing the activity of antibacterial agents in vivo soon after bone infection.