Sensitivity of Escherichia coli to Seaweed (Ascophyllum nodosum) Phlorotannins and Terrestrial Tannins

This study investigated the antimicrobial effects of phlorotannins (polyphenols) extracted from Ascophyllum nodosum against E. coli O157:H7. In vitro experiments showed strong, dose-dependent inhibition: concentrations of 50 to 100 μg/mL were bactericidal, while lower levels delayed or suppressed bacterial growth.
Phlorotannins were more effective than terrestrial tannins, with some E. coli strains completely inhibited or eradicated at moderate doses. Microscopy revealed damage to bacterial cell walls, suggesting disruption of membrane structure as a key mechanism.
The findings indicate that phlorotannins are potent antimicrobial compounds and likely contribute to the reduction of E. coli shedding observed in livestock fed seaweed. Estimated rumen concentrations from typical supplementation could reach levels sufficient for antimicrobial activity, although in vivo effects may be attenuated by the complexity of the rumen environment.
Overall, the study highlights phlorotannins as a key functional component of seaweed with strong potential for pathogen control in animal systems.