Bacterial Biofilms in Infective Endocarditis – A complex in vitro - Model to Investigate Emerging Technologies of Antimicrobial Cardiovascular Device Coatings

Abstract

<p><strong>Objective:</strong> Most biofilm flow-chambers are designed for standardized homogeneous biofilms for research purposes. These do not mimic the complexity of prosthetic heart valves, which consist of both artificial and biological material.</p> <p>Infective endocarditis (IE) is still associated with a high morbidity and mortality. IE is characterized by bacterial biofilms of the endocardium leading to destruction of the valve. Current research demonstrates that about one quarter of the patients with formal surgery indication cannot undergo surgery. This group of patients needs further options of therapy, but due to a lack of models for IE, prospects of research are low.</p> <p>Therefore, the purpose of this project was to establish an in vitro - model of infective endocarditis to allow growth of bacterial biofilms on porcine aortic valves, serving as baseline for further research.</p> <p><strong>Methods and Results: </strong>A pulsatile two-chamber circulation model was constructed that kept native porcine aortic valves under sterile, physiologic hemodynamic and temperature conditions. To exclude external contamination, sterility tests with sterile culture media were performed for 24h. During this time period, no growth of microorganisms was observed in the system and cultures after plating on standard media remained negative.</p> <p>The system was inoculated with Staphylococcus epidermidis PIA 8400 to create biofilms on porcine aortic valves. Porcine aortic roots were incubated in this system for increasing periods of time and bacterial titration to evaluate bacterial growth and biofilm development on the valves. After incubation, specimens were embedded and tissue sections were analyzed by Fluorescence in situ hybridization (FISH) for direct visualization of the biofilms and bacterial activity.</p> <p>Pilot tests for biofilm growth showed monospecies colonization consisting of cocci with time- and inocula-dependent increase. FISH visualized biofilms with ribosome-containing, and thus metabolic active cocci, tissue infiltration and similar colonization pattern as observed by FISH in human IE heart valves infected by S. epidermidis.</p> <p><strong>Conclusion:</strong> These results demonstrate the establishment of a novel complex in vitro - model for bacterial biofilm growth on porcine aortic roots. The model will allow identifying predilection sites of heart valves for bacterial adhesion and biofilm growth and it may serve as baseline for further research on IE therapy and prevention, e.g. the development of antimicrobial transcatheter approaches to IE.</p>