Bioburden after S. aureus Inoculation in Type-1 Diabetic Rats Undergoing Internal Fixation

Fracture stabilization in the diabetic patient is associated with higher complication rates, particularly infection and impaired wound healing, which can lead to major tissue damage, osteomyelitis, and higher amputation rates. With an increasing prevalence of diabetes and an aging population, the risks of infection of internal fixation devices are expected to grow. Although numerous retrospective clinical studies have identified a relationship between diabetes and infection, currently there are few animal models that have been used to investigate postoperative surgical site infections associated with internal fixator implantation and diabetes. We therefore refined the protocol for inducing hyperglycemia and compared the bacterial burden in controls to pharmacologically induced type-1 diabetic rats after undergoing internal fracture plate fixation and Staphylococcus aureus surgical site inoculation. Using an initial series of streptozotocin doses, followed by optional additional doses to reach a target blood glucose range of 300–600 mg/dl, we reliably induced diabetes in 100% of the rats (n=16) who maintained a narrow hyperglycemic range 14 days after onset of diabetes (466 ± 16 mg/dl, mean ± SEM; coefficient of variation = 0.15). With respect to our primary endpoint, we quantified a significantly higher infectious burden in inoculated diabetic animals (median 3.2 × 10 10 CFU/mg dry tissue) when compared to inoculated non-diabetics (7.2 × 10 4 CFU/mg dry tissue). These data support our hypothesis that uncontrolled diabetes adversely affects the immune system’s ability to clear S. aureus associated with internal hardware.