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Updated: Aug 9, 2026
Animal Model of Implant-Associated Infections in Mice
Published on: June 27, 2025
Comparison and evaluation of experimental mediastinitis models: precolonized foreign body implants and bacterial
Gulden Ersoz1, Barlas Naim Aytacoglu, Nehir Sucu
1Department of Clinical Microbiology and Infectious Diseases, Mersin University, School of Medicine, Mersin, Turkey. gersoz@mersin.edu.tr
Background:
Post-sternotomy mediastinitis (PSM) is a devastating surgical complication affecting 1-3% of patients that undergo cardiac surgery. Staphylococcus aureus is one of the most commonly encountered bacterial pathogen cultured from mediastinal samples obtained from patients with PSM. A component of the membrane of the gram positive bacteria, lipoteichoic acid, stimulates the blood monocytes and macrophages to secrete cytokines, radicals and nitrogen species leading to oxido-inflammatory damage. This seems to be responsible for the high mortality rate in PSM. For the evaluation of the pathogenesis of infection or for the investigation of alternative treatment models in infection, no standard model of mediastinitis seems to be available. In this study, we evaluated four mediastinitis models in rats.
Methods:
The rats were divided into four groups to form different infection models. Group A: A suspension of 1 x 107 colony-forming units Staphylococcus aureus in 0,5 mL was inoculated from the right second intercostal space into the mediastinum. Group B: A hole was created in the right second intercostal space and a piece of stainless-steel implant with a length of 0.5 cm was inserted into the mediastinum and a suspension of 1 x 107 cfu bacteria in 0,5 mL was administered via the tail vein. Group C: Precolonized stainless-steel implant was inserted into the mediastinum. Group D: Precolonized stainless-steel implant was inserted into the mediastinum and the bacteria suspension was also injected into the mediastinum. On the 10th day, rats were sacrificed and the extension of infection in the mediastenae was evaluated by quantitative cultures. Myeloperoxidase activity (MPO) and malondialdehyde (MDA) levels were determined in the sera to evaluate the neutrophil activation and assess the inflammatory oxidation.
Results:
The degree of infection in group C and D were 83.3% and 100% respectively (P < 0.001). MDA levels were significantly higher in these two groups than the others (P < 0.001).
Conclusion:
Infected implants and high bacterial concentration administration were the two important components that played a significant role in the outcome of a successful infection in mediastinum in a rat model.
Insights
Developing a reliable rat model for post-sternotomy mediastinitis (PSM) is crucial. Infected implants and high bacterial loads significantly increase infection rates, aiding PSM research.
Area of Science:
- Surgical Complications
- Infectious Disease Pathogenesis
- Animal Models in Research
Background:
- Post-sternotomy mediastinitis (PSM) is a severe complication of cardiac surgery, occurring in 1-3% of patients.
- Staphylococcus aureus is a common pathogen in PSM, with its lipoteichoic acid component driving oxido-inflammatory damage and high mortality.
- A standardized animal model for PSM is lacking, hindering research into pathogenesis and treatment.
Purpose of the Study:
- To evaluate four distinct rat models for inducing post-sternotomy mediastinitis.
- To identify key factors contributing to successful mediastinitis induction in a preclinical setting.
- To provide a foundation for future research on PSM pathogenesis and novel therapeutic strategies.
Main Methods:
- Four groups of rats were used to create different mediastinitis models, involving Staphylococcus aureus inoculation and/or pre-colonized stainless-steel implants.
- Infection was assessed on day 10 via quantitative cultures of mediastinal tissue.
- Biomarkers of neutrophil activation (MPO) and oxidative stress (MDA) were measured in serum.
Main Results:
- Groups C (infected implant) and D (infected implant with bacterial injection) showed significantly higher infection rates (83.3% and 100%, respectively) compared to other groups.
- Malondialdehyde (MDA) levels, indicating oxidative stress, were significantly elevated in groups C and D.
- These findings highlight the critical role of infected implants and bacterial load in establishing mediastinitis in the rat model.
Conclusions:
- The study successfully established and compared four rat models for post-sternotomy mediastinitis.
- Infected implants and high bacterial concentrations are essential for creating a robust and reproducible mediastinitis model.
- This validated model can be utilized for further investigation into PSM pathogenesis and the development of new treatments.
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