Inactivation of bacteria and yeast using high-frequency ultrasound treatment

• Bacteria and yeast in water were treated by high-frequency ultrasound.
• High-frequency ultrasound is efficient for the inactivation of bacteria.
• The inactivation is due to the production of free radicals and H2O2.
• The inactivation process continues even after ultrasonic processing is stopped.
• Rod-shaped bacterium Bacillus subtilis was also sensitive to mechanical forces.

High-frequency (850 kHz) ultrasound was used to inactivate bacteria and yeast at different growth phases under controlled temperature conditions. Three species of bacteria, Enterobacter aerogenes, Bacillus subtilis and Staphylococcus epidermidis as well as a yeast, Aureobasidium pullulans were considered. The study shows that high-frequency ultrasound is highly efficient in inactivating the bacteria in both their exponential and stationary growth phases, and inactivation rates of more than 99% were achieved. TEM observation suggests that the mechanism of bacteria inactivation is mainly due to acoustic cavitation generated free radicals and H2O2. The rod-shaped bacterium B. subtilis was also found to be sensitive to the mechanical effects of acoustic cavitation. The study showed that the inactivation process continued even after ultrasonic processing cessed due to the presence of H2O2, generated during acoustic cavitation. Compared to bacteria, the yeast A. pullulans was found to be more resistant to high-frequency ultrasound treatment.

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