Synergistic effect of fucoidan with antibiotics against oral pathogenic bacteria

Background: Fucoidan is a sulphated polysaccharide that is primarily extracted from brown seaweeds; it has been broadly studied in recent years due to its numerous biological properties, including anticoagulant, antithrombotic, antitumour and antiviral activities. Objective and design: In this study, fucoidan was evaluated against oral bacteria, either alone or with antibiotics, via the broth dilution method and chequerboard and time-kill assay. Results: Minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC) values for the fucoidan against all the tested bacteria ranged between 0.125 and 0.50/0.25 and 1.00 mg ml^-1, for ampicillin 0.125 and 64/0.5 and 64 μg ml^-1 and for gentamicin 2 and 256/4 and 512 μg ml ^-1, respectively. Furthermore, the MIC and MBC were reduced to one half-eighth as a result of the combination of the fucoidan with antibiotics. One to 3 h of treatment with MIC₅₀ of fucoidan with MIC₅₀ of antibiotics resulted from an increase of the rate of killing in colony forming units (CFUs) ml^-1 to a greater degree than was observed with alone. Conclusion: These results suggest that fucoidan is important in the antibacterial actions of the agents.