This study aimed to investigate the synergistic bactericidal effect and mechanism of ultrasound combined with ultraviolet against Escherichia coli O157:H7. The inactivation kinetics was modeled, ultrastructural changes in bacterial cells were examined as well as alterations in the properties of the cell membrane, and oxidative stress levels were determined. The results revealed that after 40 s of combined treatment, the bacterial count was reduced by 8.3 (lg (CFU/mL)). Significant impairment of cell morphology and leakage of cellular contents were observed. The combined treatment induced a cellular stress response within a short period of time, characterized by increased cellular esterase activity, ATP content and levels of reactive oxygen species (ROS) along with DNA damage. In conclusion, combined treatment with ultrasound and ultraviolet synergistically exerted a significant bactericidal effect. Ultrasound-induced cavitation enhances structural damage to cells, enabling ultraviolet to directly act on DNA. Moreover, both treatments work together to exacerbate oxidative stress, thereby interfering with cellular metabolism and exerting a synergistic bactericidal effect.

This study analyzed the differentially expressed genes (DEGs) of Escherichia coli O157:H7 after combined ultrasound and ultraviolet (US+UV) treatment to explore molecular inactivation mechanisms. A total of 2,133 genes showed differential expression, including 1,055 up-regulated and 1,078 down-regulated genes, indicating pronounced transcriptomic changes. Functional enrichment analyses based on Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases demonstrated that these DEGs were mainly associated with pathways related to carbohydrate metabolism and transport, the tricarboxylic acid (TCA) cycle, amino acid synthesis, oxidative phosphorylation, and quorum sensing. Notably, TCA cycle-related genes (frdD, frdB) were significantly up-regulated, which likely enhanced electron flow into the oxidative phosphorylation pathway, thereby promoting ATP synthesis and energy production to counteract stress-induced damage. Conversely, genes related to ABC transporters (e.g., fepB, malK) and ribosomal proteins (e.g., rplK, rpsF) were markedly down-regulated, indicating that disrupted membrane transport and protein synthesis under stress conditions. Furthermore, the up-regulation of quorum sensing genes (e.g., lsrC, lsrK) indicated enhanced intercellular communication, possibly linked to stress adaptation. Overall, US+UV treatment exerted a profound impact on multiple metabolic and regulatory pathways, leading to cellular dysfunction and potentially cell death. The study provided valuable mechanistic insights into the synergistic bactericidal effects of non-thermal US+UV treatment and offered a molecular basis for its application in food safety interventions.

As a green non-thermal physical sterilization technology, ultrasonic can kill microorganisms in a short period of time while causing little damage to functional components in foods and maintaining food quality, making it a promising candidate for application in the food industry. Spores, a dormant form of vegetative cells with strong resistance to various processing techniques and sanitizers, are difficult to inactivate, attributable to its dense structure. As ultrasonic has only a limited killing effect on spores, many studies have applied a combination of ultrasonic and other sterilization technologies to kill spores. This review focuses on the killing effect and mechanism of ultrasonic alone and in combination with other sterilization technologies on bacterial spores. This review is expected to provide a theoretical reference for the non-thermal inactivation of bacterial spores.

Plasma-activated water (PAW) indicated promising potential in controlling the biological contamination of Bacillus cereus, which eliminated its evolutionary endospore that improves its survival ability. However, the spore inactivation mechanism by PAW at molecular level was not well understood. The mechanism of the B. cereus endospore against PAW at proteomic levels was demonstrated. The Tandem Mass Tag (TMT) labeling was performed. By comparing the treatment groups with control (including PAW and PAW added superoxide dismutase (SOD)), the expression of 251 proteins (with the number of 207 up- and 44 down-regulated) and 379 proteins (with the corresponding number of 238 and 141) were drastically affected, separately. The 6 categories based on the protein-protein interaction (PPI) networks included oxidation-reduction, transport, sporulation and DNA topological change, gene expression, metabolism, and others. The 3 dehydrogenases (genes hisD, BC_2176, and asd) in PAW while oxidoreductase (genes BC_0399 and BC_2529) in SOD were activated to maintain the antioxidation of spores. The proteins (BC_4271 and BC_2655) in SOD were dramatically activated, which were involved in the carbohydrate, amino acid, and energy-coupling transport. All the small, acid-soluble spore proteins were activated in both groups to protect the spores’ DNA. In SOD, genes metG2 and rpmC also were considered important factors in translation while this role was played in gene groES but not rpmF in PAW. The PAW activated the biogenesis of cell wall/membrane/envelope and phosphorelay signal transduction system to contribute to the survival of spores whereas the SOD damaged these 2 processes as well as cell division, chromosome separation, organic acid phosphorylation, base- and nucleotide-excision repairs to lead to the death of spores. This would promise to lay the foundation for advancing the study of the intrinsic mechanism of spore killing against PAW and can also provide a reference for future verification.