Insights on the antimicrobial mechanisms of action of high power ultrasound

Abstract

High Power Ultrasound (HPU) is an emerging food preservation technology based on the principle of cavitation. This cavitational energy produces thermal, mechanical, and chemical effects capable of inactivating microorganisms. This comprehensive study investigated the mechanism of HPU-mediated inactivation by screening single-gene knockout mutants of 𝘓𝘪𝘴𝘵𝘦𝘳𝘪𝘢 𝘮𝘰𝘯𝘰𝘤𝘺𝘵𝘰𝘨𝘦𝘯𝘦𝘴 and 𝘌𝘴𝘤𝘩𝘦𝘳𝘪𝘤𝘩𝘪𝘢 𝘤𝘰𝘭𝘪. Additionally, an assessment of the extent of thermal contribution to microbial inactivation was performed by simulating the temperature change dynamics during HPU treatment. Furthermore, the effects of food matrix and pH on cellular reduction during HPU exposure were investigated. The mutant screening revealed that deletion of genes such as Δ𝘤𝘭𝘱𝘉, Δ𝘳𝘱𝘰𝘚, Δ𝘥𝘯𝘢𝘒, Δ𝘴𝘰𝘹𝘚, Δ𝘴𝘥𝘩𝘊, Δ𝘰𝘹𝘺𝘙, and Δ𝘳𝘦𝘤𝘈 resulted in reduced HPU resistance compared to the parental strain 𝘌. 𝘤𝘰𝘭𝘪 K12. In parallel, deletion of Δ𝘥𝘯𝘢𝘒, Δ𝘳𝘦𝘤𝘈, 𝘴𝘪𝘨𝘉, Δ𝘤𝘭𝘱𝘉, Δ𝘨𝘢𝘥𝘋3 and Δ𝘥𝘭𝘵𝘈 increased the sensitivity of 𝘓. 𝘮𝘰𝘯𝘰𝘤𝘺𝘵𝘰𝘨𝘦𝘯𝘦𝘴 EGDe to HPU exposure. Our findings reveal that thermal effects during HPU treatment under dynamic temperature conditions significantly contribute to microbial inactivation. HPU treatment using pine apple juice demonstrated that the properties of the food matrix can have a substantial effect on inactivation, with higher inactivation levels observed in pineapple juice compared to broth medium. Overall, the findings reveal novel insights into the molecular mechanism of HPU treatment, highlighting genes that may confer resistance to ultrasonic stress while also considering factors such as thermal contribution, food matrix, and pH levels. Insights from this study will be relevant for developing food safety interventions for HPU or hurdle approaches that incorporate HPU treatment.