Establishment of rat model of acute staphylococcal osteomyelitis: relationship between inoculation dose and development of osteomyelitis

Introduction Many animal models of acute and chronic osteomyelitis have been developed. In these models, osteomyelitic lesions are induced using sclerosing agents and foreign bodies with bacterial strains. In the present rat model, these sclerosing agents were not used. We assessed the relationship between inoculation dose and histological, radiological, and microbiological changes in the acute phase (1 week after inoculation) using this rat osteomyelitis model. Materials and methods An experimental rat model of acute osteomyelitis was developed by direct inoculation of the virulent strain BB of Staphylococcus aureus into tibial bone without sclerosants. To examine the relationship between the inoculation dose of the bacteria and the progression of the osteomyelitis, the inoculated lesions were assessed for changes in histological, radiological, and bacteriological parameters at 1 week after infection. Serial dilutions of the bacteria [6x10(1) to 6x10(5) colony-forming units (CFU)/5 mu l] suspended in saline or saline alone were inoculated into the proximal metaphysis of the tibia. Results Development of significant histological and radiological signs of osteomyelitis required an inoculum of at least 6x10(3) CFU/5 mu l. The number of viable bacteria at the lesion reached a maximum of 6x10(3) CFU/5 mu l. Conclusion These results suggest that strain BB induces the development of acute staphylococcal osteomyelitis with clear infective destruction in the tibia, and that our model may be applied to the identification of virulence factors in studies of posttraumatic osteomyelitis.