Antibacterial activity and toxicity of Halymenia durvillei red seaweed from Kayangan island, South Sulawesi, Indonesia

This study aimed to determine the antibacterial activity and toxicity of methanol and hexane extracts of Halymenia durvillei red seaweed which were found abundantly in Kayangan island, South Sulawesi. The antibacterial activity of the crude extract was tested against five gram-negative bacteria, namely Escherichia coli , Salmonella typhi , Pseudomonas aeruginosa , Aeromonas hydrophila , and Vibrio harveyi at a dose of 200 g/disk. Extract toxicity was tested on Artemia salina larvae at concentrations of 1,000, 500, 250, 125, 62.5, and 31.25 µg/mL. The results showed that the methanol and hexane extracts of H. durvillei had the highest activity against S. thypi and A. hydrophila , respectively, with inhibition zones of 26.2 mm and 21.0 mm. On the other hand, the two extracts did not show activity against E. coli and P. aeruginosa , respectively. The toxicity of the methanol extract of H. durvillei was twice as high as that of the hexane extract with half-maximal inhibitory concentration of 98.24 and 184.21 µg/mL, respectively. Thus, the methanol and hexane extracts of red seaweed H. durvillei have the potential as new antibacterial agents respectively against the pathogenic bacteria S. typhi and A. hydrophila , but also have the opportunity to be developed into antitumor herbal compounds.