Antibacterial, anti-biofilm, and anti-quorum sensing effects of jujube extract against Salmonella enterica serovar typhimurium and Escherichia coli O157:H7

Compounds derived from plants can serve as antibacterial agents in medications and food preservatives. However, little is known about their ability to interfere with bacterial communication systems that control biofilm formation and virulence. This study aimed to investigate the antibacterial, anti-biofilm, and, for the first time, anti-quorum sensing activities of Ziziphus jujuba (jujube) extract against two major foodborne pathogens, Salmonella enterica serovar Typhimurium (S. Typhimurium) and Escherichia coli O157:H7. The antibacterial activity was evaluated using the microbroth dilution method to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The anti-biofilm efficacy of jujube extract at sub-MIC concentrations was assessed against S. Typhimurium and E. coli O157:H7 utilizing the microtiter plate (MTP) assay and scanning electron microscopy (SEM). Finally, the expression of genes related to quorum sensing and biofilm formation was examined upon exposure to sub-MIC concentrations of jujube extract by real-time PCR. The MIC and MBC values for E. coli O157:H7 were 625 μg/mL, while for S. Typhimurium, they were 1250 μg/mL. Both SEM and MTP assays displayed acceptable inhibitory and disruption activity of the jujube extract on the biofilm formation at sub-MIC concentration. Real-time PCR revealed a decrease in the expression of genes (csgA, FimA, pfs, and LuxS) in E. coli O157:H7 and (csgD, sdiA) in S. Typhimurium upon exposure to jujube extract at 312.5 μg/mL and 625 μg/mL, respectively. The novelty of this research lies in demonstrating, for the first time, the anti-quorum sensing activity of jujube extract against foodborne pathogens. Compared with previous reports that focused mainly on antibacterial effects, this work provides molecular evidence of how jujube extract interferes with quorum sensing and biofilm formation. Given the antibacterial, anti-biofilm, and anti-quorum sensing activities of jujube extract, this study highlights its potential advantage as a natural antimicrobial agent against strong biofilm-producing bacteria.