Abstract
Cinnamic acid (CA) is a safe and effective antimicrobial agent. The objective of this study was to reveal the antibacterial mechanism of CA against a food-derived Pseudomonas fragi 38-8, from the aspects of bacterial growth kinetics, cell membrane homeostasis, cell microstructure, and transcription. The minimum inhibitory concentration (MIC) of CA against P. fragi 38-8 was 0.25 mg/ml. CA retarded bacterial growth and induced a series of cell membrane changes. After CA treatment, cell membrane homeostasis was destroyed, which was evidenced by cell membrane depolarization, intracellular pH reduction, and intracellular ATPase activity decrease. Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and confocal laser scanning fluorescence microscope (CLSM) realized the visualization of cell microstructure changes, showing cell death and morphological changes, such as cell rupture, shrinkage, and hollowness. RNA sequencing analysis further confirmed the effects of CA to the cell membrane, because of the significant enrichment of differentially expressed genes (DEGs) related to membrane. The results of the phenotype tests and RNA-seq both focused on cell membrane damage, which showed that CA exerted antibacterial effect mainly by acting on cell membrane.
Highlights
The genus Pseudomonas can usually cause food spoilage by shorting shelf life of fresh products, especially during cold storage, with a high economic burden for food industries (Quintieri et al, 2020)
A published study has shown that Cinnamic acid (CA) has a good antibacterial effect on Alicyclobacillus acidoterrestris (Cai et al, 2015)
As an active natural product with highefficiency bacteriostatic activity, it was necessary to conduct an in-depth study on the antibacterial mechanism of CA against P. fragi 38-8
Summary
The genus Pseudomonas can usually cause food spoilage by shorting shelf life of fresh products, especially during cold storage, with a high economic burden for food industries (Quintieri et al, 2020). Pseudomonas fragi is a facultative anaerobic and Gram-negative bacterium that is able to grow between 2 and 35°C (Ercolini et al, 2010) Their high spoilage potential is due to extracellular proteases and lipases (Zhang et al, 2019b), which act on foods, resulting in changes in the physicochemical and organoleptic properties. This kind of psychrotrophic bacterium has often been detected in some spoiled milk, meat, and seafood (Papadopoulou et al, 2020), in food in the cold chain, where the P. fragi occupies a dominant position. It is urgent to take effective measures against P. fragi to reduce the economic loss within the cold chain
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