Effective Prevention of Microbial Biofilm Formation on Medical Devices by Low-Energy Surface Acoustic Waves

Abstract

Low-energy surface acoustic waves generated from electrically activated piezo elements are shown to effectively prevent microbial biofilm formation on indwelling medical devices. The development of biofilms by four different bacteria and Candida species is prevented when such elastic waves with amplitudes in the nanometer range are applied. Acoustic-wave-activated Foley catheters have all their surfaces vibrating with longitudinal and transversal dispersion vectors homogeneously surrounding the catheter surfaces. The acoustic waves at the surface are repulsive to bacteria and interfere with the docking and attachment of planktonic microorganisms to solid surfaces that constitute the initial phases of microbial biofilm development. FimH-mediated adhesion of uropathogenic Escherichia coli to guinea pig erythrocytes was prevented at power densities below thresholds that activate bacterial force sensor mechanisms. Elevated power densities dramatically enhanced red blood cell aggregation. We inserted Foley urinary catheters attached with elastic-wave-generating actuators into the urinary tracts of male rabbits. The treatment with the elastic acoustic waves maintained urine sterility for up to 9 days compared to 2 days in control catheterized animals. Scanning electron microscopy and bioburden analyses revealed diminished biofilm development on these catheters. The ability to prevent biofilm formation on indwelling devices and catheters can benefit the implanted medical device industry.Indwelling device-related infections constitute a major cause of morbidity and mortality in hospitalized patients, adding considerably to medical costs. Microbial biofilms readily develop on all types of devices, urinary, endotracheal, intravenous, and other types of catheters and implants inserted into more than 25% of patients during hospitalization. The incidence of bacterial infections in patients with urinary catheters is approximately 5 to 10% per day, with virtually all patients who undergo long-term catheterization (Ն28 days) becoming infected (13,14,17).The first stage in biofilm formation from planktonic microorganisms is attachment to solid surfaces (6). Attachment stimulates microbial aggregation and proliferation to form microcolonies. The colonies excrete an encasing exopolysaccharide "slime," which consolidates the attachment to surfaces, and the microaggregates differentiate into characteristic biofilms (20). Quorum-sensing molecules that generate concentration gradient-dependent signals that control and alter expression of a large number of genes also aid biofilm differentiation (15,25). Encasing the extracellular polysaccharide matrix of biofilms regulates exchange of ions and nutrients with the surrounding environment. This regulation contributes to increases of up to 1,000-fold in biofilm resistance to antibiotics compared to planktonic bacteria (9, 11) and protects the biofilms from biocides, surfactants, and predators. Microbial biofilms also present serious challenges to the immune system because expression of bac...

Electrical methods of controlling bacterial adhesion and biofilm on device surfaces

“…Potentially, this is difficult to consistently achieve and would constitute a significant risk to any in vivo applications. Hazan et al demonstrated what might be considered the most advanced step towards achieving clinical implementation using acoustic energy to date in a rabbit model where catheters utilizing piezo-electric actuators remained sterile for up to 9 days whilst all controls developed UTIs [85]. Further studies must be carried out to develop a matrix of which acoustic treatment parameters are effective at targeting a broad range of bacterial species.…”

“…Novel efforts have been made to combat device-related bacterial infections by using acoustic energy at specific frequencies to either prevent biofilm formation on surfaces or to mechanically compromise the structures of existing biofilms [85,86]. Acoustic energy holds a number of key advantages over other methods as it can prove an effective means of bypassing the conditioning-film and hence preventing any surface adhesion occurring in the first place since the mechanical disruptions render any firm surface attachment much more difficult.…”

“…The need for a more sophisticated approach to the application of acoustic energy has already resulted in a novel solution which fine-tunes vibration energy using tiny piezo-electric elements. Hazan et al developed piezoelectric elements attached to the outer surface of a catheter (FIGURE 7), which spread low-energy acoustic waves (for example 0.2 mW/cm 2 ) throughout the device and surrounding fluid media causing the bacteria to vibrate at the same frequency [85]. This has the effect of covering the catheter in a vibrating "coat" which facilitates biofilm prevention inspite of the usual inhibitors that develop on urinary catheters such as conditioning films encrusted with proteins, electrolytes and other organic molecules [98,99].…”

“…Another promising development utilizes advanced RF treatment fields to prevent initial bacterial growth (and produce an RF bioelectric effect) [29,69,70], whilst a further novel approach was developed using piezo-electric actuators to set up antimicrobial acoustic waves on IMD surfaces preventing biofilm formation in vivo [85]. Further work must be carried out to optimize the electric field parameters and conducting polymer combinations (such that the device surface would effectively act as the electrode) required to effectively combat the pathogens responsible for nosocomial infections such as UTIs.…”

Superchannel of Bacteria: Biological Significance and New Horizons

“…The antigenicity of the alginate lyase must be considered before the enzyme can be developed for clinical use. Recently, it was reported that ultrasonic vibrations block bacterial biofilms from forming on medical devices, 70) although physical processes must be constructed to maintain continuous vibration to prevent biofilm formation.…”