Fucoidans from Laminaria hyperborea demonstrate bactericidal activity against diverse bacteria

Fucoidans are a heterogenous class of fucose-rich sulfated carbohydrates which have attracted increasing attention in cancer
and infammation research due to their bioactive properties. There are reports that fucoidans may have direct antibacterial
efects and synergy with antibiotics. However, the literature is conficting, potentially due to the limited reporting of origin,
characteristics, and extraction methods of the fucoidans tested. Here we report the results of 18 defned fucoidans screened for
direct, indirect, and synergistic antibacterial efects. 15 distinct fucoidan fractions, isolated from Laminaria hyperborea using a
solvent-free extraction process, were characterised for molecular weight, pH, viscosity, and sulfur content. These, together with
three commercially available crude fractions, were assessed at concentrations from 0.03125-24 mg mL-1 for minimum inhibitory concentration against Staphylococcus aureus, Streptococcus mutans and Streptococcus sanguinis. Furthermore, we tested a selection of fucoidans for antibacterial synergy with vancomycin and indirect antibacterial efects in whole blood survival assays. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was performed to assess the stress response in fucoidan-treated S. aureus cultures. We have identifed one fucoidan fraction with bactericidal activity against diverse bacteria.
This efect is dose-, fucoidan fraction- and bacteria-specifc, and furthermore, not related to osmotic stress. No synergistic efects were observed with fucoidan in combination vancomycin. Fucoidans have exciting potential as antimicrobial agents. Further analysis is required to establish the precise molecular characteristics responsible for their potent bactericidal activity.