Combating resilient Acanthamoeba castellanii cysts: Ultrasonic frequency-dependent effects on viability and excystment

Free-living amoebae (FLA) are significant environmental reservoirs for numerous pathogenic microorganisms. These protists exhibit remarkable resilience, often evading biocides due to their ability to form highly resistant dormant cysts under unfavorable conditions. This study investigated the effects of ultrasound treatment on the viability of these amoeba cysts, using Acanthamoeba castellanii, a prevalent water and soil amoeba, as a model. We found that low-frequency ultrasound treatment significantly impaired the revival of Acanthamoeba cysts. In contrast, high-frequency ultrasound effectively ruptured cyst walls and induced direct amoebal death. Further investigation using tert-Butanol, an OH radical scavenger, partially mitigated the effects induced by high-frequency ultrasound, demonstrating that reactive oxygen species contribute to amoeba damages. Our results highlight ultrasound's significant potential as an efficient and effective strategy to combat resilient Acanthamoeba cysts.