Antibacterial activity of Indonesian red algae Gracilaria edulis against bacterial fish pathogens and characterization of active fractions.

In this study the crude ethyl acetate extracts and fractions from red algae Gracilaria edulis were studied against fish pathogens. G. edulis was extracted with ethyl acetate, fractionated in silica gel coloum chromatography and gradient hexane-ethyl acetate. The extract and fractions were subjected for bioassay guided isolation against fish pathogen Vibrio spp and Aeromonas hydrophila. Bioassays were accomplished by diffusion agar, bioauthography, and 96 well microplates format. Profiling chemical constituent was done by thin layer chromatography and GC-MS. Metabolites analysis using GC-MS yielded chemical constituents of active fractions as 9-hexadecenoic acid, hexadecanoic acid, 13-octadecenoic acid, 10-octadecenoic acid, eicosanoic acid, cholest-8-en-3-ol. The results provide in vitro scientific support to the possible application of Gracilaria edulis as antimicrobial agent that may contribute for treatment of bacterial infections in aquaculture.