Abstract
ObjectiveIn spite of the progress in antimicrobial and surgical therapy, 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 their destruction. About one quarter of 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 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.Methods and resultsA pulsatile two-chamber circulation model was constructed that kept native porcine aortic valves under sterile, physiologic hemodynamic and temperature conditions. To create biofilms on porcine aortic valves the system was inoculated with Staphylococcus epidermidis PIA 8400. Aortic roots were incubated in the model for increasing periods of time (24 h and 40 h) and bacterial titration (1.5 × 104 CFU/mL and 1.5 × 105 CFU/mL) with 5 L cardiac output per minute. After incubation, tissue sections were analysed by fluorescence in situ hybridization (FISH) for direct visualization of the biofilms. Pilot tests for biofilm growth showed monospecies colonization consisting of cocci with time- and inocula-dependent increase after 24 h and 40 h (n = 4). In n = 3 experiments for 24 h, with the same inocula, FISH visualized biofilms with ribosome-containing, and thus metabolic active cocci, tissue infiltration and similar colonization pattern as observed by the FISH in human IE heart valves infected by S. epidermidis.ConclusionThese results demonstrate the establishment of a novel in vitro model for bacterial biofilm growth on porcine aortic roots mimicking IE. The model will allow to identify predilection sites of 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.Graphic abstract
Highlights
Despite recent advances in antimicrobial as well as surgical therapy, infective endocarditis (IE) remains a major clinical problem with mortality rates of 20–25% [2, 11, 28, 29]
In n = 3 experiments for 24 h, with the same inocula, fluorescence in situ hybridization (FISH) visualized biofilms with ribosome-containing, and metabolic active cocci, tissue infiltration and similar colonization pattern as observed by the FISH in human IE heart valves infected by S. epidermidis. These results demonstrate the establishment of a novel in vitro model for bacterial biofilm growth on porcine aortic roots mimicking IE
FISH analysis of n = 2 porcine aortic valves after 7 days incubation in 0.6% GA revealed no active microorganisms at the valve and after incubation of n = 3 in Tryptone soy broth without dextrose (TSB) Bouillon for 48 h no microbial growth was observed in Bouillon as well as after plating the Bouillon on agar plates
Summary
Despite recent advances in antimicrobial as well as surgical therapy, infective endocarditis (IE) remains a major clinical problem with mortality rates of 20–25% [2, 11, 28, 29]. As pharmacological and surgical treatment concepts are frequently ineffective, novel preventive and therapeutic treatment approaches are needed. Prior to human application extensive preclinical evaluation of novel treatments in representative models of endocarditis is required. When bacteria colonize endocardial tissue they form biofilms, which represent complex communities embedded into a matrix of secreted macromolecules [12]. The biofilm represents a protective environment for bacteria to tolerate systemic antibiotics and host phagocytic defenses. The resulting recalcitrance towards antibiotic treatment poses a significant problem in endocarditis
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