A localized vertebral infection model of pyogenic spondylitis induced by Staphylococcus aureus in rats.

Background and purpose: Pyogenic spondylitis (PS) is clinically challenging and induces disastrous consequences for patients. The pathogenesis of PS is difficult to explore due to a lack of ideal animal models. Thus, we aimed to reproduce the local pathogenesis of PS in an innovative animal model induced by Staphylococcus aureus.

Methods: Rats were injected with planktonic Staphylococcus aureus (ATCC 25923) and grouped according to different concentrations. We identified the optimal bacterial inoculum concentration based on general physical signs and radiological, hematological, and histological parameters in rats. Models with the optimal bacterial concentration were used to investigate changes in physical, radiological, and inflammatory parameters at different time points.

Results: Our results revealed that infected rats experienced rapid weight loss, high fever, and significantly increased white blood cell count, interleukin 1β, and C-reactive protein (CRP) levels in the short term. Radiographic examination revealed bone damage in groups that received 2 × 10³/20 μl, 2 × 10⁵/20 μl and 2 × 10⁷/20 μl bacterial concentrations. The optimal concentration was identified as 2 × 10⁵/20 μl, based on the high survival rate, obvious bone destruction, and inflammation. Histological staining confirmed the living bacteria, inflammatory cells, bone destruction, and scarce bone formation in infected vertebrae.

Conclusions: This study provides an innovative PS animal model that simulates a local iatrogenic vertebral infection and develops innovative and effective strategies for its treatment, but does not simulate the hematogenous dissemination characteristics of most clinical cases of pyogenic spondylitis.