Quantitative assessment of the germicidal efficacy of ultrasonic energy

TLDR

Ultrasonic energy at 26 kHz was applied to aqueous suspensions of bacteria, fungus, and viruses, with transient cavitation identified as the inactivation mechanism. Exposure time and intensity increased bacterial kill rates, reduced fungal growth, and inactivated feline herpesvirus, while having no effect on feline calicivirus, indicating that low‑kHz ultrasound can partially inactivate select waterborne pathogens.

Abstract

Propagated (free-field) ultrasonic energy at a frequency of 26 kHz was used to expose aqueous suspensions of bacteria (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa), fungus (Trichophyton mentagrophytes), and viruses (feline herpesvirus type 1 and feline calicivirus) to evaluate the germicidal efficacy of ultrasound. There was a significant effect of time for all four bacteria, with percent killed increasing with increased duration of exposure, and a significant effect of intensity for all bacteria except E. coli, with percent killed increasing with increased intensity level. There was a significant reduction in fungal growth compared with that in the controls, with decreased growth with increased ultrasound intensity. There was a significant reduction for feline herpesvirus with intensity, but there was no apparent effect of ultrasound on feline calicivirus. These results suggest that ultrasound in the low-kilohertz frequency range is capable to some degree of inactivating certain disease agents that may reside in water. The physical mechanism of inactivation appears to be transient cavitation.