Transcriptomic Response of Listeria monocytogenes and Salmonella enterica Typhimurium to Power Ultrasound and Chlorine Treatments

Listeria monocytogenes and Salmonella enterica Typhimurium are leading causes of foodborne illness in the United States and frequently implicated in produce outbreaks. Conventional decontamination methods, such as cold-water washes with chlorine, have limited antibacterial efficacy and environmental sustainability. Power ultrasound has emerged as a promising non-thermal alternative, but the molecular mechanisms remain insufficiently elucidated. This study evaluated transcriptomic responses of L. monocytogenes and S. enterica Typhimurium to (i) ultrasound (20 kHz), (ii) chlorine (50 ppm), and (iii) combined ultrasound + chlorine treatments. RNA-seq analysis identified differentially expressed genes, as well as enriched Gene Ontology and KEGG terms. Results showed that ultrasound and chlorine triggered distinct transcriptomic responses. L. monocytogenes exhibited broad transcriptional shifts under ultrasound, including significant upregulation of phosphotransferase system components and central metabolism. Chlorine alone induced a narrower response, with fewer differentially expressed genes clustering into limited functional categories. In contrast, the combined ultrasound + chlorine treatment elicited the strongest response in S. enterica Typhimurium, with enrichment of multiple energy- and metabolism-related pathways, including the citrate cycle, carbon metabolism, and microbial metabolism in diverse environments. These findings provide new insights into ultrasound-triggered responses in foodborne pathogens and may inform development of optimized ultrasound-based hurdle sanitization strategies for produce safety.