CHARACTERIZATION OF A RABBIT MODEL OF STAPHYLOCOCCAL OSTEOMYELITIS

We previously described a rabbit osteomyelitis model that involved the direct introduction of Staphylococcus aureus into devascularized bone . To further evaluate the model, we performed experiments aimed at cor relating the microbiological, radiographic, and histologic parameters involved in the development of experimental osteomyelitis. Using the s train UAMS-1, we achieved an infection rate of 75% with an inoculum as small as 2 x 10(3) colony-forming units. However, development of sign ificant radiographic and histologic signs of disease: required an inoc ulum of at least 2 x 10(4) colony-forming units. Radiographic signs we re minimal 1 week after infection and progressed steadily to a maximum 3 weeks after infection. In contrast. histologic signs of disease wer e observed within 1 week and remained essentially unchanged throughout the: 4-week evaluation period. Unlike the results obtained with UAMS- 1, rabbits infected with the heavily encapsulated Staphylococcus aureu s strain Smith diffuse exhibited little evidence of disease even when infected with 2 x 10(6) colony-forming units. The reduced virulence of strain Smith diffuse was surprising given its greatly enhanced virule nce (relative to UAMS-1) in a murine peritonitis model of staphylococc al disease. These results suggest that UAMS-1 expresses virulence fact ors that are important in the pathogenesis of osteomyelitis and that s ome or all of these virulence factors are either absent or are nut exp ressed in strain Smith diffuse, Most importantly the results suggest t hat our model may be appropriate for the identification and characteri zation of these virulence factors.