Evaluation of the Phytochemical Components and Antimicrobial Property of Gracilaria edulis Extracts Against Selected Aquaculture Pathogenic Bacteria

With pathogenic bacteria in aquaculture becoming increasingly resistant to antibiotics, there is a compelling need to look into bioactive chemicals present in seaweed as novel treatment options for fish infections. The purpose of this study was to evaluate the phytochemical characteristics of G. edulis extracts and its antimicrobial activities against selected aquaculture pathogenic bacteria. Phytochemical screening of G. edulis was carried out following qualitative test tube screening methods. The antimicrobial activities of the methanolic and ethanolic extracts of G. edulis were tested using the paper disc agar diffusion method against Aeromonas hydrophila, Escherichia coli, and Staphylococcus aureus. Amoxicillin and distilled water were used as a positive and negative control respectively. Based on the phytochemical analysis, the methanolic crude extract of G. edulis contained tannins and flavonoids while the ethanolic crude extract included only tannins. Further, the results of the antimicrobial assay test showed that both methanolic and ethanolic extracts of G. edulis inhibited the bacteria with inhibitory activity comparable to that of the positive control (Amoxicillin). The study therefore suggests that G. edulis can further be investigated for the possible formulation of therapeutics and drugs in light of its potential as an antibacterial agent.