In vitro evaluation of antibiofilm activity of crude extracts from macroalgae against pathogens relevant in aquaculture

The exploitation of macroalgal biomass could provide novel environment-friendly molecules to prevent bacterial biofilm formation. Crude extracts, or polysaccharides, from the DNA-barcoded macroalgae Chaetomorpha aerea (Chlorophyta), and Agardhiella subulata and Hypnea cornuta (Rhodophyta) collected from the coastal brackish Lake of Ganzirri (Italy) were evaluated for their effects on biofilm formation of Listonella anguillarum, Vibrio harveyi, V. parahaemolyticus and Photobacterium damselae subsp. piscicida. All bacterial strains were able to produce biofilm on polystyrene surfaces at different extents. Without exerting antibacterial activity, the crude polysaccharides showed dose-dependent inhibitory activity on the biofilm formation. At the highest concentration (400 μg/ml), the strongest reduction of biofilm formation was observed in the presence of C. aerea and A. subulata extracts against V. harveyi (59 and 53%, respectively), followed by the H. cornuta extract against P. piscicida (52%) and V. parahaemolyticus (28%). The extract from A. subulata was also active against the biofilm formation of P. piscicida (48%) and L. anguillarum (33%). As resulted by the surface coating assay and the microbial adhesion onto hydrocarbons, the algal extracts were able to inhibit the adhesion of pathogens and modify their cell-surface properties and hydrophobicity. Moreover, all the extracts possessed high emulsifying activity (E24 up to 70%) and stabilizing capacity. Based on two different in vivo assays, using Artemia salina and Danio rerio, all the extracts showed no potential toxicity for aquaculture application. Our results suggest that the antibiofilm activity of algal extracts is related to the inhibition of the early bacterial adhesion. Consequently, these non-toxic and biodegradable polysaccharides, with surfactant and antiadhesive properties, could be proposed to prevent biofilms in aquaculture.