Abstract
This study evaluated the effect of the combination of ultrasound and phenyllactic acid (PLA) on inactivating Staphylococcus aureus and Salmonella enteritidis biofilm cells and determined the possible antibiofilm mechanism. S. aureus and S. enteritidis biofilm cells were separately treated with ultrasound (US, 270 W), phenyllactic acid (PLA, 0.5% and 1%), and their combination (US + 0.5% PLA, and US + 1% PLA) for 5, 10, 20, 30, and 60 min. Biofilm inactivation, polysaccharide, and respiratory chain dehydrogenase assays were conducted. US and PLA had a synergistic effect on inactivating bacterial cells in S. aureus and S. enteritidis biofilms. The combination of US and PLA significantly decreased the contents of soluble and insoluble polysaccharides and the activity of respiratory chain dehydrogenase in the biofilm cells compared to the single treatment. Confocal laser scanning microscopy, scanning electron microscopy, and intracellular adenosine-triphosphate (ATP) analyses indicated that the combination of US and PLA seriously destroyed the cell membrane integrity of the S. aureus and S. enteritidis biofilms and caused the leakage of intracellular ATP. These findings demonstrated the synergistic antibiofilm effect of US combined with PLA and offered a research basis for its application in the food industry.
Highlights
Food safety has been a serious threat to people’s health given the frequent outbreak of foodborne diseases and has attracted increasing attention worldwide [1]
The combined treatment of Ultrasonic sterilization (US) + 0.5% phenyllactic acid (PLA) for 5 and 30 min inactivated S. aureus biofilm cells by 1.7 and 3.4 log CFU/mL, respectively, similar to the 1% PLA treatment. These results showed that the combined treatment of ultrasound and PLA was significantly more effective than the single treatment (p < 0.05)
Ultrasound combined with PLA was more effective in inactivating S. enteritidis biofilm cells than the single treatment
Summary
Food safety has been a serious threat to people’s health given the frequent outbreak of foodborne diseases and has attracted increasing attention worldwide [1]. Foodborne pathogens, such as Staphylococcus aureus and Salmonella enteritidis, are of worldwide concern due to their latent hazards to food security and public hygiene [2]. S. aureus and S. enteritidis can form biofilms on solid surfaces [4,5]. The formation of biofilms provides protection for foodborne pathogens and ensures that bacterial cells can adapt to unfavorable growth conditions. The elimination of pathogen biofilms is the key to ensure food safety
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