Antimicrobial effect and mechanism of Sargassum carpophyllum extract against fish spoilage Pseudomonas sp. CL2

Components of marine macroalgae have been considered as a novel source of antimicrobial and food preservatives. In the present study, the antibacterial activity and mechanism of Sargassum carpophyllum extract against fish spoilage Pseudomonas sp. CL2 has been studied. The minimum inhibitory concentration (MIC) of the extract was 3.20 mg dry mass (DM)/mL, and time-kill assay revealed that the antibacterial activity was dependent on the dose and treatment period. Changes in bacterial molecular composition have been revealed by Fourier transform infrared spectroscopy (FTIR). The protein and phospholipid structure of the bacteria have been altered, and leakage of nucleic acids was detected. These results were further confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of membrane protein, fatty acid analysis and cell membrane permeability assays. The intensity of 25–30 kDa protein bands and ratio of unsaturated fatty acids to saturated fatty acids have been increased by the extract treatment, suggesting alterations in membrane protein and the fatty acid composition. Other than nucleic acid, leakage of proteins and small ions, as well as alkaline phosphatase (AKP) activity were also detected as the sign of increased cell membrane permeability. Scanning electron microscopy (SEM) images also evidenced the fact that S. carpophyllum extract has impaired the cell integrity and caused cell lysis. The results of the present study indicated that the extract could inhibit Pseudomonas sp. CL2 through damaging cell integrity and altering membrane permeability, which would provide important knowledge to understand the antibacterial mechanism and development of new antimicrobial product from S. carpophyllum.