Selective antimicrobial potential of fucoidans against the pathogen Listeria monocytogenes

Listeria monocytogenes is a gram-positive facultative intracellular foodborne pathogen capable of causing severe infection, particularly in immunocompromised and elderly populations. Infection typically begins at the gastrointestinal mucosa, where L. monocytogenes employs a range of virulence factors to enable its adhesion and translocation across the intestinal epithelial barrier. L. monocytogenes is equipped with virulence factors known as internalins, a family of proteins which play a key role in facilitating the adhesion and invasion of host cells. In this study, we investigate the anti-adhesive and anti-invasive potential and mode of action of fucoidan derived from Macrocystis pyrifera and Undaria pinnatifida against L. monocytogenes. Fucoidan from M. pyrifera significantly inhibited adhesion of L. monocytogenes NCTC 5348 to HT-29 intestinal epithelial cells in a concentration-dependent manner, while fucoidan from U. pinnatifida showed a modest but non-significant reduction in adhesion. In contrast, both fucoidans significantly reduced bacterial invasion, resulting in reductions of 71.8 ± 9.3% and 40.8 ± 11.7%, respectively (p < 0.05), indicating inhibition of early infection events, likely adhesion. Further analysis of fucoidan from M. pyrifera against a panel of 11 additional L. monocytogenes strains demonstrated strong inhibitory activity against the LO28 strain, reducing adhesion by 53.0 ± 11.8% (p < 0.05). Interestingly, the 12 strains employed in this study had genetically diverse internalin profiles with fucoidan-susceptible LO28 possessing a similar internalin profile to NCTC 5348. This strain-specific activity observed suggests that fucoidan from M. pyrifera primarily acts on the bacteria to inhibit adhesion to gastrointestinal cells, and that its presence during infection is required to achieve maximum anti-adhesive efficacy. This study highlights the importance of fucoidan structure in determining bioactivity and identifies both fucoidan from M. pyrifera and U. pinnatifida as strain-specific anti-invasive ingredients against L. monocytogenes infection.