Effects of acoustic streaming from moderate-intensity pulsed ultrasound for enhancing biofilm mitigation effectiveness of drug-loaded liposomes

Because biofilms have resistance to antibiotics, their control using minimum amounts of chemicals and energy becomes a critical issue particularly for resource-constrained long-term space and deep-sea explorations. This preliminary study investigates how ultrasound promoting penetration of antibiotic-loaded liposomes into alginate-based bacterial biofilms, resulting in enhanced bacterial ( Ralstonia insidiosa) killing. Nano-sized liposomes are used as a delivery vehicle for the antibiotic gentamicin. Alginate-based synthetic biofilms, which are widely acknowledged as biofilm phantoms, filled with liposome solution are formed at the bottoms of six-well Petri dishes and exposed to ultrasound ( frequency = 2.25 MHz, 10% duty cycle, and spatially and temporally averaged intensity I-SAPA = 4.4W/cm(2)). Gentamicin is released from liposomes after they are lysed using detergent solution ( 0.05% sodium dodecyl sulfate, 1.0% Triton X-100) and incubated for 20 min. The alginate biofilm is dissolved and diluted, counting of colony-forming units shows about 80% of the bacteria are killed. It has also been shown the liposome-capture density by the alginate film increases linearly with the ultrasound intensity up to I-SAPA = 6.2W/cm(2) reaching approximately threefold that without ultrasound. Measurement by using particle-image velocimetry has demonstrated the acoustic streaming with modification by thermal convection controls the enhancement of the liposome capture rate. (C) 2015 Acoustical Society of America.