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Infective endocarditis (IE) is still associated with a high morbidity and mortality. IE is characterized by bacterial biofilms of the endocardium, especially of the aortic and mitral valve leading to destruction of the valve. Current research demonstrate 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. Therefore, the purpose of this project is to establish an in vitro-model of infective endocarditis to allow growth of standardized bacterial biofilms on porcine aortic valves, serving as baseline for further research.
Methods and Results
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, repeated (n=5) sterility tests with sterile culture media were performed for 24h with 5l cardiac output per minute. After this time period, no macroscopic growth of microorganisms was observed, and cultures after plating on standard media remained negative. To create biofilms on porcine aortic valves, the system was inoculated with Staphylococcus epidermidis. Porcine aortic roots were incubated in this system for increasing periods of time (8h, 24h and 40h) 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 pathogen detection and visualization of the biofilms. The monospecies colonization was confirmed by culture and 16S rRNA-PCR with sequencing. The pilot tests for biofilm growth showed coccoid biofilms with time- dependent increasing growth after 8h, 24h and 40h. One of the 40h experiment performed PCR showed S. epidermidis as only pathogen of the biofilm with a matching genotype of 99%. The other n=3 experiments for biofilm creation showed biofilms with active cocci, good tissue infiltration and similar colonization pattern after 40h.
These results demonstrate the efficacy of the above in vitro-model for bacterial biofilm growth on porcine aortic roots. The model will allow identification of predilection sites of valves for bacterial adhesion and biofilm growth, and it may serve as baseline for further research on infective endocarditis therapy, e.g. the development of antimicrobial transcatheter approaches to IE.