Antibacterial Potential of Aqueous Extracts and Compounds from Selected Brown Seaweeds

Background: The incident of antibacterial resistance is increasing rapidly. Seaweeds, the marine macroalgae that are rich in bioactive compounds have the potential to be applied as an antimicrobial agent. Objective: The objective was to assess the potential of brown seaweed aqueous extracts (Sargassum polycystum and Padina australis) and commercial pure compounds (alginic acid and fucoidan) as antimicrobial agent toward Gram-negative bacteria such as Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa as well as Gram-positive bacteria, Staphylococcus aureus. Methods: Powdered brown seaweeds were macerated with distilled water and followed by filtration. The aqueous extracts were recovered by ethanol precipitation, oven-dried, and stored at 4°C. Aqueous extracts were examined for their qualitative phytochemical content and antibacterial susceptibility test using Kirby–Bauer method. Results: S. polycystum was reported for higher extraction yield (7.00%) than P. australis (1.40%). The presence of steroid, phytosterols, and phenols was observed in S. polycystum extract while steroid and phytosterols were observed in P. australis extract. In antibacterial susceptibility test, there was no inhibition shown by both seaweed extracts against the four bacteria tested. Fucoidan (0.50 mol/L) and alginic acid (0.50 mol/L) were observed to have antibacterial property against S. aureus (with inhibition zone of 7.43±0.17 mm and 7.45±0.14 mm, respectively). Conclusion: The aqueous extracts of S. polycystum and P. australis have shown low antibacterial activity, as compared to fucoidan and alginic acid. Further studies on the mode of antibacterial activity possessed by fucoidan and alginic acid will be carried out.