Microbial biofilm modulation by ultrasound: Current concepts and controversies

Abstract

Biofilm elimination is often necessary during antimicrobial therapy or industrial medical manufacturing decontamination. In this context, ultrasound treatment has been frequently described in the literature for its antibiofilm effectiveness, but at the same time, various authors have described ultrasound as a formidable enhancer of bacterial viability. This discrepancy has found no solution in the current literature for around 9 years; some works have shown that every time bacteria are exposed to an ultrasonic field, both destruction and stimulation phenomena co-exist. This co-existence proves to have different final effects based on various factors such as: ultrasound frequency and intensity, the bacterial species involved, the material used for ultrasound diffusion, the presence of cavitation effects and the forms of bacterial planktonic or biofilm. The aim of this work is to analyze current concepts regarding ultrasound effect on prokaryotic cells, and in particular ultrasound activity on bacterial biofilm.

Inactivation of Planktonic Escherichia coli by Focused 2-MHz Ultrasound

“…1995). Still others have focused on biofilm treatment (Erriu et a l. 2014). As an example of the latter, Xu et al (2012) conducted in vitro studies of the destruction and removal of biofilms comprised of the gram-negative bacterium Pseudomonas aeruginosa , motivated by the problem of biofilm growth on implanted prostheses.…”

Microbicidal Activity of Artificially Generated Hydroxyl Radicals

“…The antimicrobial effect of ultrasound has been studied in various fields, such as water treatment, food decontamination and medical disinfection [59]. The mechanism of killing microorganisms is mainly due to cavitation effect in which tiny gas bubbles formed in liquid medium by alternating compression and expansion collide violently, creating shock waves in a localized region with high temperature (5,500 C) and pressure (50 MPa) [60].…”

Interplay Between Mechanochemistry and Sonochemistry

“…bacterial viability may be enhanced under sonication. The subject has been recently reviewed and it was found that both effects depend on factors such as frequency, intensity, materials used for ultrasound diffusion, the presence or absence of cavitation, as well as the type of bacteria [105]. The combined use of therapeutic ultrasound with antibiotics usually decreases bacterial viability in vitro and in vivo [106].…”