Ultrasound Triggered Microbubble Destruction for Disrupting Biofilms in Synovial Fluid

This study investigated the combination of antibiotics and ultrasound triggered microbubble destruction (UTMD) to disrupt free-floating bacterial biofilms in synovial fluid (SynF) of infected joints. In vitro, 1×10
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colony forming units (CFU) of S. aureus aggregated in human SynF had 100 μL of Definity® (Lantheus Medical Imaging, N Billerica, MA, USA), and 30 μg/mL of amikacin added. Samples were insonated either at a high MI of 1.06 for 10 min or a low MI of 0.04 for 6 min. In vivo, 6 pigs (mean weight 35 kg) had their left femorotibial joint inoculated with 1×10
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CFU of S. aureus. A SynF sample was collected from all animals 24 hrs post-inoculation. Control animals (2) received amikacin (250 mg) into the joint, while the remaining animals received 100 μL of Definity and 1 mL of amikacin. UTMD was performed using an S9 Pro scanner with a curvilinear probe (SonoScape, Shenzhen, China) and a flash replenishment sequence (MI <; 0.15) with 4 s destructive pulses (MI > 0.6) for the duration of contrast visualization. SynF samples were collected from all animals after the therapeutic intervention for cytological analysis and quantitative bacteriology. UTMD and antibiotics resulted in large decreases in bacterial numbers (>2-4 logs) in vitro compared to antibiotic alone. In vivo the infection protocol consistently caused clinical septic arthritis by 24 hrs post-inoculation. Nucleated cell counts and cytology parameters were all consistent with septic arthritis. Floating bacterial aggregates were occasionally observed in the joint aspirates obtained prior to UTMD. No biofloats were detected on joint aspirates obtained following intra-articular therapy and no bacterial growth was noted in any dilutions in the post-treatment SynF samples, while pre-treatment samples and amikacin only animals presented with bacterial counts of greater than 2000 CFU/mL. In conclusion, UTMD demonstrates synergism with antimicrobials against SynF biofilm aggregates.