Antibacterial activity and HPLC analysis of extracts from Mediterranean brown algae

The antibacterial activity of methanolic extracts of eight Mediterranean brown algae belonging to the genera Cystoseira sensu lato, Dictyopteris and Padina was investigated. Extracts from Sargassaceae showed antibacterial activity. Specifically, Carpodesmia crinita and Carpodesmia brachycarpa extracts inhibited the growth of the Gram-positive strain Kocuria rhizophila whereas Cystoseira compressa and Carpodesmia amentacea extracts showed antibacterial activity against the Gram-positive strains, Kocuria rhizophila and Staphylococcus aureus. None of them inhibited the growth of the Gram-negative bacterium Escherichia coli. The extracts of Cystoseira sp. pl. and Treptacantha ballesterosii did not show any antibacterial activity. HPLC-MS analysis of the extracts allowed identification of polar compounds. Taxa of the genus Cystoseira sensu lato showed a higher number of compounds than Dictyopteris poly- podioides and Padina pavonica. Some differences found among and within taxa can be attributed to the different depths where these algae live, to thallus morphology and herbivore pressure. Particularly interesting were the phenol compounds, which showed differences among the genera but also within the genus Cystoseira sensu lato. Noteworthy, the almost exclusive presence of the fukiik acid isomer and of bromo-phloroglucinol in Carpodesmia amentacea, and the presence of exifone, able to bind iron metal ions, in Carpodesmia amentacea, Cystoseira compressa and Treptacantha ballesterosii.