Transcription profiles and phenotype reveal global response of Staphylococcus aureus exposed to ultrasound and ultraviolet stressors

Ultrasound and ultraviolet light have good inactivation performance against pathogens in sewage. In this study, the inactivation mechanisms of 60 kHz ultrasound and ultraviolet radiation against Staphylococcus aureus (S. aureus) were studied from the perspectives of cell phenotype and transcriptome for the first time. The results showed that both ultrasound and ultraviolet treatments had adverse impacts on the cellular morphology of S. aureus to varying degrees at cellular level. The transcriptomic analysis revealed that there were 225 and 1077 differentially expressed genes (DEGs) in the ultrasound and ultraviolet treatments, respectively. The result revealed that both ultrasound and ultraviolet could interfere with the expression of the genes involved in ABC transporters, amino acid and fatty acid metabolism to influence the membrane permeability. Besides the membrane permeability, ultraviolet also could disturb the ATP synthesis, DNA replication and cell division through restraining the expression of several genes related to carbohydrate metabolism, peptidoglycan synthesis, DNA-binding/repair protein synthesis. Compared with the single inactivation pathway of ultrasound, ultraviolet inactivation of S. aureus is multi-target and multi-pathway. We believe that the bactericidal mechanisms of ultrasound and ultraviolet radiation presented by this study could provide theoretical guidance for the synergistic inactivation of pathogens in sewage by ultrasound and ultraviolet radiation in the future.

Microbial decontamination assisted by ultrasound-based processing technologies in food and model systems: A review

Ultrasound (US) technology is recognized as one of the emerging technologies that arise from the current trends for improving nutritional and organoleptic properties while providing food safety. However, when applying the US alone, higher power and longer treatment times than conventional thermal treatments are needed to achieve a comparable level of microbial inactivation. This results in risks, damaging food products' composition, structure, or sensory properties, and can lead to higher processing costs. Therefore, the US has often been investigated in combination with other approaches, like heating at mild temperatures and/or treatments at elevated pressure, use of antimicrobial substances, or other emerging technologies (e.g., high-pressure processing, pulsed electric fields, nonthermal plasma, or microwaves). A combination of US with different approaches has been reported to be less energy and time consuming. This manuscript aims to provide a broad review of the microbial inactivation efficacy of US technology in different food matrices and model systems. In particular, emphasis is given to the US in combination with the two most industrially viable physical processes, that is, heating at mild temperatures and/or treatments at elevated pressure, resulting in techniques known as thermosonication, manosonication, and manothermosonication. The available literature is reviewed, and critically discussed, and potential research gaps are identified. Additionally, discussions on the US's inactivation mechanisms and lethal effects are included. Finally, mathematical modeling approaches of microbial inactivation kinetics due to US-based processing technologies are also outlined. Overall, this review focuses only on the uses of the US and its combinations with other processes relevant to microbial food decontamination.

Combined Hurdle Technologies Using UVC Waterproof LED for Inactivating Foodborne Pathogens on Fresh-Cut Fruits

This study investigated the combined bactericidal efficacy of slightly acidic electrolyzed water (SAEW), fumaric acid (FA), and ultravioletC waterproof light-emitting diodes (UVC W-LED) for the control of Staphylococcus aureus and Listeria monocytogenes in fresh-cut fruits. Cherry tomato, grape, apple, and pineapple were inoculated with S. aureus and L. monocytogenes and then washed with 30 ppm SAEW containing 0.5% FA in a container equipped with two UVC W-LEDs. Behaviors of S. aureus and L. monocytogenes and quality properties of fresh-cut fruits were monitored after storage at 10 °C and 15 °C for 7 days. The most effective reductions of S. aureus (1.65 log CFU/g) and L. monocytogenes (2.63 log CFU/g) were observed in the group with the combined treatment of SAEW + FA and UVC W-LED. At 10 °C and 15 °C, populations of both pathogens in the combined treatment group were lower than those in a control. Combined treatment showed no negative effect on moisture retention in the fruit. Moreover, visual changes were less significant than in the control. These results demonstrate that the combined treatment can improve the microbial safety and the quality of fruits. If it is properly used in the sanitizing step of the fresh produce industry, a positive effect can be expected.