# The Role of Fucoidan in Controlling _Listeria monocytogenes_ Biofilms on Seafood-Contact Surfaces
## 4 Discussion  
The effectiveness of fucoidan in preventing _L. monocytogenes_ inhibition of biofilm on abiotic surfaces and examined its possible modes of action. The findings showed that fucoidan significantly inhibited biofilm development and disrupted already-formed biofilms, even at concentrations below the MIC. Fucoidan, a sulfated polysaccharide extracted from _Fucus vesiculosus_, is known for its antimicrobial activity against various foodborne pathogens and dental plaque bacteria [30,31]. Earlier research has reported MIC values for fucoidan between 125 and 1000 \(\upmu\)g/mL [32]. Regarding its antibiofilm effects, 250 \(\upmu\)g/mL were particularly efficient in suppressing of _Streptococcus mutans_ and _S. sobrinus_ biofilm formation and planktonic cells [32]. Data highlight the prospect of fucoidan as an environmental antibacterial negotiator suitable for applications in the seafood processing industry. Biofilm formation on abiotic surfaces tips to persistent contamination and resistance to conventional sanitation methods, presenting ongoing challenges in seafood production [33]. In the current study, fucoidan significantly reduced _L. monocytogenes_ biofilm formation on HG, SR, and SS surfaces, with the most pronounced effects monitored at 1/2 MIC and MIC levels (see Figures 1-3). Comparable antibiofilm effects of fucoidan have also been reported against _Staphylococcus aureus_ and _Escherichia coli_[34]. The MIC of 150 \(\upmu\)g/mL for _L. monocytogenes_ identified here aligns with previous findings for Gram-negative bacteria like _Pseudomonas aeruginosa_ and _E. coli_, which reported MIC values between 100 and 200 \(\upmu\)g/mL [35]. These observations support the broad-spectrum and concentration-dependent antibacterial activity of fucoidan. Notably, the biofilm-associated bacterial counts were reduced by up to 2.91 log CFU/cm\({}^{2}\) on HG, 2.46 log CFU/cm\({}^{2}\) on SR, and 2.11 log CFU/cm\({}^{2}\) on SS surfaces. In addition, the antimicrobial efficacy of fucoidan F85 was evaluated against _Streptococcus mutans_ in Brain Heart Infusion (BHI) broth at 0 to 250 \(\upmu\)g/mL. The untreated group, which served as a baseline for bacterial growth, demonstrated a substantial proliferation--rising from an initial inoculum of approximately 5.2 log CFU/mL to around 8.6 log CFU/mL within 18 h. This elevated bacterial load remained stable over the next 30 h, with only a modest decline of about 1 log unit observed by the 48 h mark, likely due to nutrient depletion or accumulation of toxic metabolic by-products. Conversely, treatment with fucoidan at 125 \(\upmu\)g/mL presented a strong bacteriostatic effect, completely inhibiting the growth of _S. mutans_ throughout the 48 h incubation period. Notably, the highest tested concentration (250 \(\upmu\)g/mL) exerted a pronounced bactericidal action, resulting in a sustained and progressive decline in viable cell counts. By the end of the 48 h period, the bacterial population had dropped to approximately 3.3 log CFU/mL--indicating a substantial reduction both the untreated control and the lower concentration group [22]. These findings highlight not only the dose-dependent antimicrobial activity of fucoidan but also its dual functional potential: as a growth inhibitor at moderate concentrations and as a bactericidal agent at higher doses. The progressive decrease in viable bacterial counts at 250 \(\upmu\)g/mL suggests membrane disruption or interference with critical cellular processes, meriting further mechanistic studies. This research underscores the potential application of fucoidan as an effective natural antimicrobial, especially for targeting oral pathogens like _S. mutans_, and potentially extending its utility to foodborne pathogens and biofilm-related contamination in food systems [32]. In addition to its inhibitory effects on biofilm formation, fucoidan also downregulated genes (_flaA_, _fgp_, _prfA_, _hhyA_, and _agrA_) in _L. monocytogenes_ biofilms. These genes play critical roles in bacterial communication, biofilm formation, and pathogenicity.