A rat model of Staphylococcus aureus chronic osteomyelitis that provides a suitable system for studying the human infection

Chronic osteomyelitis was produced by inoculating Staphylococcus aureus into rat tibia. The infection was characterised grossly by bone deformation and histopathologically by inflammation and the presence of coccal organisms sequestered within the bone tissue. Further observations by scanning electronmicroscopy demonstrated bacteria in microcolonies surrounded by dehydrated amorphous material that was considered to be glycocalyx. Transmission electronmicroscopy, when aided by antibody stabilisation, revealed extensive glycocalyx production within the tibia. These findings indicate that the rat model of chronic S. aureus osteomyelitis mimics the human infection with respect to the sessile mode of growth of bacteria within the bone. Serum antibody levels were assayed by ELISA and immunoblotting procedures. After an initial increase, ELISA titres remained relatively stable, apparently indicating the establishment of chronic osteomyelitis, whereas in immunoblotting an increase in titre over the course of infection was observed. Whole-cell ELISA revealed less subtle differences in antibody titre than did immunoblotting with cell-wall antigen. We found that mid-range antigens, including an antigen implicated as protein A, featured prominently in the immune response in this model of infection.