Microbial biofilm modulation by ultrasound: Current concepts and controversies

•Effects of ultrasound on bacterial biofilms are dependent on several factors.•To define the relationship between ultrasonic and bacteria, the literature from 1927 was analyzed.•An analysis of the literature it was possible to highlight a dual effect of “life or death”.•In conclusion, it was assessed what characteristics of ultrasound and bacterial biofilms could explain this dual effect. 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 9years; 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.