Incidence of infection in implanted polyurethane tubing segments serially injected with staphylococci

One of the major clinical complications in the biomedical application of synthetic materials is the incidence of implant-associated infections. Such infections are very often induced by Staphylococcus aureus. To obtain information on tissue reactions and minimal bacterial challenge needed to create an infection related to untreated implant surfaces, we injected polyurethane tubing segments with a series of Staphylococcus aureus. The segments were subcutaneously implanted in rats. Implantation periods varied from 2, 5 and 10 days to 3 weeks. Specimen were evaluated using light and transmission electron microscopy. At least 0.25×10⁴ of Staphylococci aureus were needed to clearly recognize that bacteria had been injected in the polyurethane tubing segments. The evidence was indirect, showing high infiltration and activation of neutrophils and macrophages, but not bacteria. Furthermore, 0.25×10⁶ S. aureus were needed to induce a persistent specific inflammatory reaction with high concentrations of lymphocytes, i.e. mainly plasma-cells, at 3 weeks. The results indicate that this model functioned well to obtain the wanted information. Results are discussed with respect to (a-) specific inflammatory reactions occurring with (bacterial-challenged) biomaterials. Ultimately, our goal is to develop infection-resistant materials, for which the in vivo model developed may be used to qualify the processed materials