Evaluation of antibacterial properties of Laurencia obtusa and Cystoseira barbata against some bacterial fish pathogens

Document Type : Original Article


1 1Department. of Aquatic Animal Medicine, Faculty of Veterinary Medicine, Benha University 2 National Services Project Organization, Armed forces, Egypt

2 Department. of Aquatic Animal Medicine, Faculty of Veterinary Medicine, Benha University

3 Fish Biology and Ecology Department, Central Lab for Aquaculture Research Center, Giza, Egypt


The present study aimed to evaluate the antibacterial efficacy of the ethanolic extracts derived from two marine seaweeds; namely Laurencia obtusa (LOEE) and Cystoseira barbata (CBEE) using agar disc diffusion test. The seaweeds were extracted using 95% ethanol then analyzed using Gas chromatography–mass spectrometry (GC–MS). A total of 97 and 86 compounds were found in LOEE, and CBEE consequently. The predominant metabolites found in both seaweeds were; Palmitic acid, Palmitic acid ethyl ester, Butyl glycol, Heptadecane, Tetradecane, Valeric acid, Diethyl phthalate, Hexanoic acid ethyl ester, Ethylene glycol, Eicosane, and Ethyl oleate. These metabolites are known for their antibacterial properties against various fish pathogens. To assess the antimicrobial effects of the seaweed extract, three bacterial strains that cause disease in fish were selected; Streptococcus iniae (S. iniae), Aeromonas hydrophila (A. hydrophila), and Aeromonas veronii (A. veronii) and one nonpathogenic bacterium for fish Staphylococcus epidermidis (Staph. epidermidis) as a reference. Based on the recorded data, it was observed that LOEE shown superior antibacterial properties compared to CBEE. The LOEE exhibited the largest zone of inhibition, measuring 19.67 ± 0.64 mm, against Staph. epidermidis. The agar plates streaked with S. iniae had the smallest inhibitory zones, measuring (8.27± 0.14 mm) and (8.37± 0.14 mm) for LOEE and CBEE, respectively. The activity index (AI) showed that LOEE exhibited the maximum inhibition of 0.84 mm and 0.65 mm against Staph. epidermidis and A. hydrophila, respectively. Overall, LOEE was effective in suppressing the growth of the majority of the examined bacteria invitro, as compared to CBEE.


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