Antibacterial Activity of Sargassum Longifolium and Gracilaria Corticata from Gulf of Mannar against Selected Common Shrimp Pathogens

The antibacterial activity of crude extracts of Sargassum longifolium and Gracilaria corticata collected from the Gulf of Mannar Coast, Tamilnadu, India against common shrimp pathogens were tested by disc diffusion method. Three different solvents namely aqueous, ethanol and methanol were used for extraction. The qualitative phytochemical analysis revealed the presence of carbohydrates, proteins, alkaloids, glycosides, terpenoids, flavonoids, tannin, saponins and steroids in the crude extracts. Different concentration of the crude extracts of Sargassum longifolium and Gracilaria corticata showed antibacterial activity against common shrimp pathogens such as Aeromonas hydrophilia, Pseudomonas aeruginosa, Vibrio cholerae, V. harveyi, and V. parahaemolyticus. The methanol extract showed better results than the other extracts. Methanol extract of Gracilaria corticata showed maximum activity against P. aeruginosa (20.75 ± 0.5) and V. parahaemolyticus (18.75 ± 0.5 mm) at 800 μg/disc. V. cholerae has highly sensitive (21.25 ± 0.5 mm) against methanol extract of S. longifolium (800 μg/disc). Aqueous extracts of both seaweeds showed low activity against all the tested bacteria. These results show the potentials of seaweeds G. corticata and S. longifolium for screening of antibacterial compounds.