Stimulated phase-shift acoustic nanodroplets enhance vancomycin efficacy against methicillin-resistant <em>Staphylococcus aureus</em> biofilms

Abstract

Purpose Bacterial biofilms on the surface of prostheses are becoming a rising concern in managing prosthetic joint infections. The inherent resistant features of biofilms render traditional antimicrobial therapy unproductive and revision surgery outcomes uncertain. This situation has prompted the exploration of novel antimicrobial strategies. The synergy of ultrasound microbubbles and vancomycin has been proposed as an efficient alternative for biofilm eradication. The purpose of this study was to evaluate the anti-biofilm effect of stimulated phase-shift acoustic nanodroplets (NDs) combined with vancomycin. Materials and methods We fabricated lipid phase-shift NDs with a core of liquid perfluoropentane. A new phase change mode for NDs incorporating an initial unfocused low-intensity pulsed ultrasound for 5 minutes and a subsequent incubation at 37°C into a 24-hour duration was developed. Methicillin-resistant Staphylococcus aureus (MRSA) biofilms were incubated with vancomycin and NDs under the hybrid stimulation. Biofilm morphology following treatment was determined using confocal laser scanning microscopy and scanning electron microscopy. Resazurin assay was used to quantify bactericidal efficacy against MRSA biofilm bacteria. Results NDs treated sequentially with ultrasound and heating at 37°C achieved gradual and substantial ND vaporization and cavitation in a successive process. NDs after stimulation were capable of generating stronger destruction on biofilm structure which was best characterized by residual circular arc margins and more dead bacteria. Furthermore, NDs combined with vancomycin contributed to significantly decreasing the metabolic activity of bacteria in MRSA biofilms ( P <0.05). Conclusion Phase-shift acoustic NDs could exert a significant bactericidal effect against MRSA biofilms through a new stimulation mode. Acoustic NDs present advantages over microbubbles for biofilm damage. This anti-biofilm strategy could be used either alone or as an enhancer of traditional antibiotics in the control of prosthetic joint infections.

Sonobactericide: An Emerging Treatment Strategy for Bacterial Infections

“…Scanning electron microscopy ( Fig. 5) was also used to complement confocal findings 2013, Zhu et al 2013Li et al 2015;Guo et al 2017;Dong et al 2018;Zhou et al 2018). For transmission microscopy, sample preparation of biofilms required removal from culture plate; thus, the biofilms were mechanically scraped, which could alter cellular structure (Hu et al, 2018b).…”

“…Changes in biofilm metabolism, in response to different treatments, were measured by confocal imaging with 5-cyano-2,3-ditolyltetrazolium chloride dye (Hu et al, 2018b), a CO 2 -evolution monitoring system (Ronan et al 2016) or an absorbance-based resazurin assay (Guo et al 2017;Fu et al 2019). Although investigation of cellular metabolism provides an indication of the overall bio-effect, the growth rate, biomass, cell viability and persister development could not be specified.…”

“…The authors sterilized their formulation using ultraviolet light. The nanodroplets (mean diameter: 309 nm) made by Guo et al (2017) consisted of a core of perfluoropentane and a coating of lipids. Microbubbles (mean diameter: 1.5 mm) containing a C 3 F 8 gas core and coating of the same lipids were also produced.…”

“…Nanoscale cavitation nucleating agents such as nanodroplets and polymeric nanocups (Kwan et al 2015) could be interesting for sonobactericide as they could penetrate the biofilm and help nucleate cavitation throughout the biofilm. In particular, the process of droplet vaporization may exert mechanical forces on the biofilm in addition to antibiotic activity (Guo et al 2017). Nanodroplets can nucleate sustained cavitation in closed fluid spaces .…”

Harnessing Ultrasound-Stimulated Phase Change Contrast Agents to Improve Antibiotic Efficacy Against Methicillin-Resistant Staphylococcus aureus Biofilms

“…We hypothesized that PCCAs may be more efficient than microbubbles at penetrating biofilms due to their relatively small size and increased stability. The use of US-PCCAs has previously shown to increase vancomycin killing of MRSA biofilms 41 . In contrast to the current study, Hu et al used perfluoropentane as the perfluorocarbon core, which requires higher pressures than OFP to vaporize.…”