Sonobactericide - An Adjunct Therapy for Infective Endocarditis: An In Vitro Proof-of-Concept

Abstract

Infective endocarditis (IE) is associated with high morbidity and mortality rates. The predominant bacteria causing IE is Staphylococcus aureus (S. aureus), which can bind to existing thrombi on heart valves and generate vegetations (biofilms). In this in vitro study, we evaluated sonobactericide as a novel strategy to treat IE, using ultrasound and an ultrasound contrast agent in combination with an antibiotic and a thrombolytic. We developed a model of IE vegetations using human whole-blood clots infected with S. aureus. Histology and live-cell imaging revealed an outer biofilm layer of fibrin-embedded living Staphylococci around a dense erythrocyte core. Infected clots were treated under flow for 30 minutes and degradation was assessed by time-lapse microscopy imaging. Treatments consisted of either continuous plasma flow alone or with different combinations of therapeutics: oxacillin (antibiotic), recombinant tissue plasminogen activator (rt-PA; thrombolytic), intermittent continuous-wave low-frequency ultrasound (120-kHz, 0.44 MPa peak-to-peak pressure), and an ultrasound contrast agent (Definity®). Infected clots exposed to the combination of oxacillin, rt-PA, ultrasound, and Definity achieved 99.3 ± 1.7% clot width loss, which was greater than the other treatment arms. Size measurements of the effluent suggested low emboli risk. These results demonstrate that sonobactericide could be an effective therapeutic strategy for treating IE.