Development of an in vitro soft tissue infection model related to percutaneous medical devices

Examensarbete för masterexamen
Master Thesis
Wallerstedt, Madeleine
Biomaterial associated infection (BAI) is a common and serious complication in permanent implant situations or other long-term tissue-biomaterial interactions. Established infections are frequently persistent and hard to fight with current antimicrobial approaches. Formation of bacerial biofilm on the biomaterial surface is generally considered the key factor but recent studies have come to question the strong focus on surface adhered bacteria.It is suggested that bacterial colonization of tissue surrounding the device may have more importance to the persistent nature of BAI. Patients with percutaneous medical devices (e.g external fixators and intravascular catheters) are extra sensitive to BAI. It is also well recognized that biomaterial presence itself reduces immune system efficiency. As a consequence there is a need for more research on the role of infections related to percutaneous medical devices and other BAI. This requires relevant infection models for in vitro studies to reduce the distance to animal models when testing novel antimicrobial modifications of biomaterials. However, there seems to be a lack of in vitro infection models that simulate the condition of the soft tissue surrounding percutaneous medical devices and other biomaterials. This master thesis describes an early phase development of a novel in vitro model simulating a soft tissue infection related to percutaneous medical devices. This model makes it possible to analyze bacterial colonization of both the biomaterial and the surrounding medium mimicking soft tissue extra cellular matrix. The model comprises a collagen matrix in which a contaminated model biomaterial is incubated. Segments of silver-coated and non-coated silicon urinary catheters were used as model biomaterials. In order to mimic a contamination during a surgical prcedure, the catheter segments were submerged for a short time in diluted bacteria culture before insertion in the collagen matrix. This study included the bacterial Staphylococcus aureus and Pseudomonas aeruginosa. Bacterial quantification was performed primarily with plate count method. Even small concentrations of the inoculation solution (103 cells /mL) resulted in bacterial growth on both the model biomaterial and in the surrounding collagen matrix. No significant antimicrobial effect was observed for the silver coating although a tendency to lower amount of bacteria was found on the coated catheter. In the surrounding media bacterial growth was similar for both materials. More work is of course needed to develop such in vitro infection model related to percutaneous medical devices. With a model which does not discard any bacteria during the experimental steps it is possible to observe where the bacteria are located and to which amount, both on the biomaterial and in the surrounding medium. It is likely that this in vitro model better mimic the challenges for such material in the clinical situation.
Bioinformatik och systembiologi , Livsvetenskaper , Bioinformatics and Systems Biology , Life Science
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