Enhancement of Vancomycin Activity against Biofilms by Using Ultrasound-Targeted Microbubble Destruction

Abstract

Treating biofilm infections on implanted medical devices is formidable, even with extensive antibiotic therapy. The aim of this study was to investigate whether ultrasound (US)-targeted microbubble (MB) destruction (UTMD) could enhance vancomycin activity against Staphylococcus epidermidis RP62A biofilms. Twelve-hour biofilms were treated with vancomycin combined with UTMD. The vancomycin and MB (SonoVue) were used at concentrations of 100 g/ml and 30% (vol/vol), respectively, in studies in vitro. After US exposure (0.08 MHz, 1.0 W/cm 2 , 50% duty cycle, and 10-min duration), the biofilms were cultured at 37°C for another 12 h. The results showed that many micropores were found in biofilms treated with vancomycin combined with UTMD. Biofilm densities (A 570 values) and the viable counts of S. epidermidis recovered from the biofilm were significantly decreased compared with those of any other groups. Furthermore, the highest percentage of dead cells was found, using confocal laser scanning microscopy, in the biofilm treated with vancomycin combined with UTMD. The viable counts of bacteria in biofilms in an in vivo rabbit model also confirmed the enhanced effect of vancomycin combined with UTMD. UTMD may have great potential for improving antibiotic activity against biofilm infections.Bacteria that adhere to implanted medical devices, such as vascular catheters, prosthetic joints, and artificial heart valves, can cause persistent infections because bacteria sequestered in biofilms show increased tolerance of normal antibiotic therapies (6). The mechanism of this resistance is very complicated. Current hypotheses on the subject include the heterogeneity of biofilm-encased bacteria and the failure of an antibiotic to penetrate the full depth of the biofilm (10). So far, the most effective treatment against biofilm infections is to remove the implant, treat the patient with antibiotics at safe levels, and later insert a new implant, which is a costly and difficult procedure (6, 7). Therefore, it is necessary to explore more effective methods of dealing with infections caused by biofilms on implanted devices.Studies have shown that low-frequency ultrasound (US) combined with antibiotics can significantly enhance the bactericidal activity of antibiotics in both planktonic and biofilm forms (2, 4, 12). The mechanism may be that US increases cell membrane permeability (27), enhances microconvection from ultrasonic heating, and stimulates active or passive uptake of the antibiotics, as US can give rise to high-pressure, high-shear stress, or cavitation, causing cell membrane and biofilm disruption (23, 31).Recently, microbubble (MB)-based US contrast agents have been used widely in clinical sonography. MB agents can provide nuclei for inertial cavitation and lower the threshold for US-induced cavitation. Destruction of MBs by US increases the membrane permeability of cells by shear stress, rising temperature, and activation of reactive oxygen species. Therefore, such MBs have also evolved as tools to deliver drugs or gene...

Prevention and treatment of biofilms by hybrid- and nanotechnologies

“…63 For example, US (0.08 MHz) targeted microbubble destruction of biofilm in an in vivo rabbit model enhanced the effects of vancomycin. 64 Similarly, biofilm growth in ciprofloxacin-loaded hydrogels with US induced (43 kHz ultrasonic bath for 20 minutes daily) was significantly lower compared controls. 65 Clearly, augmenting antibiotic treatment with ultrasound is a promising device combination for drug delivery to counter biofilms.…”

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

“…10,12,13 It has been recognized that MBs can present as cavitation nuclei to lower the cavitation threshold, thereby significantly facilitating transient cavitation which may generate shock waves and microjets. 31 Under such violent physical stress, high-density surfaces (eg, bacterial biofilm) become loose with emerging micropores and craters, allowing antibiotics to penetrate through the weakened matrix barrier and increase antibiotic concentration therein.…”

“…9 Recent studies have found that the cavitation-induced bactericidal effects against biofilms are based upon the cavitationally enhanced antibiotic activity within biofilms and the restored susceptibility of biofilmencapsulated cells to antibiotic action. [10][11][12][13] These effects are of high relevance to the mechanical destruction of biofilm barriers (ie, extracellular matrix), thereby promoting greater penetration of antibiotics surrounding the biofilms into the sessile bacterial community. In the setting of residual matrix scaffold, dormant cells in the deeper layer may recover metabolic activity.…”

Staphylococcus epidermidis SrrAB Regulates Bacterial Growth and Biofilm Formation Differently under Oxic and Microaerobic Conditions

“…The biofilm-forming ability of S. epidermidis strains in vivo was determined by using a New Zealand rabbit subcutaneous foreign body infection model as described by He et al with minor modifications (33). Disks were cut from polyethylene 96-well plates (8-mm diameter, 1-mm thickness, with a 2-mm projecting rim or chimb), sterilized with 75% ethanol, washed with sterile distilled water, and then disinfected by using UV light.…”

“…The biofilms were scraped from the disks, and the viable bacteria were determined by CFU counting as previously described (16,33). Five independent experiments were carried out.…”