Anti-initial adhesion activity and mechanism of mulberry (Morus alba L.) leaf polyphenols against Escherichia coli O157:H7 and Listeria monocytogenes to fresh-cut lettuce

Mulberry leaf polyphenols (MLP) has been proved to have great potential in antioxidant or antimicrobial activity. However, little is known about its anti-adhesion activity and mechanism against foodborne pathogens. This study investigated the efficacy of MLP of subminimal inhibitory concentrations (sub-MIC) in inhibiting adhesion of Escherichia coli O157:H7 and Listeria monocytogenes on fresh-cut lettuce. MLP of 1/16 MIC did not significantly affect growth of the two pathogens (p > 0.05), but it inhibited both pathogens in adhesion ratios, motility, and extracellular polymeric substances (EPS) production when added in the first 1 h (E. coli O157:H7) or 2 h (L. monocytogenes) (p < 0.05). Flagella- (both pathogens) and pili-related (E. coli O157:H7) genes were significantly downregulated when MLP was added in the first 2 h (p < 0.05). Thus, MLP prevented the biosynthesis of EPS, flagella, and pili, which in turn inhibited the initial adhesion of the two pathogens. The application of MLP is of great safety and efficiency. Therefore, MLP of low concentration can promisingly be applied to control the initial adhesion of pathogens, thoroughly eliminating foodborne pathogens in fresh produce processing.