Abstract
Seaweeds are used in pharmaceutical and biochemical applications as they possess interesting biological activities that contribute to the discovery of natural therapeutic agents. In this study, the antibacterial activity of n-hexane, dichloromethane and methanolic extracts of brown seaweeds (Phaeophyceae), Sargassum polycystum C. Agardh and Padina australis Hauck, was examined using the disc diffusion and broth microdilution methods. The bioactivity of the seaweed extracts was expressed as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The antibacterial activity against Gram-negative bacteria (beta-lactamase positive and negative Escherichia coli,Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus) was discussed. Gram-positive bacteria especially B. cereus was more susceptible to the seaweed extracts (MIC = 0.130 to 0.065 mg/ml). Generally,S. polycystum extracts exhibited higher bacteriostatic activity (lower MICs) against all the tested bacterial strains when compared with P. australis. However, P. australis extracts showed a narrow spectrum of bactericidal activity against B. cereus. n-Hexane extracts of S. polycystum exhibited promising bacteriostatic agents against B. cereus (MIC = 0.065 mg/ml) with MIC value lower than the standard MIC of potential antimicrobial drug (0.100 mg/ml). Since only crude seaweed extracts were tested in this study, further purification and isolation of bioactive compounds from the extracts are essential in future studies in order to optimize their antibacterial activity. Key words: Phaeophyceae, disc diffusion test, minimum bactericidal concentration (MBC), minimum inhibition concentration (MIC).
Highlights
The use of antibiotic for resistance of pathogenic bacteria has increased in an alarming rate
The lowest minimum inhibitory concentration (MIC) obtained from P. australis extracts against E. coli ATCC 25922, E. coli ATCC 35218, P. aeruginosa, S. aureus and B. cereus, were 0.833, 1.667, 0.261, 0.417, and 0.130 mg/ml, respectively
MICs of S. polycystum showed a similar trend compared to P. australis where both strains of E. coli were least susceptible with B. cereus the most susceptible to the seaweed extracts
Summary
The use of antibiotic for resistance of pathogenic bacteria has increased in an alarming rate. Alternative prevention and treatment are implied and natural sources such as plants and seaweeds are increasingly used. Despite the extensive studies of antibacterial activity in higher plants, seaweeds may be used as a new and promising source of bioactive compounds in the field of medical and biochemical applications (Leary et al, 2009). Biological compounds extracted from some seaweed species, namely, Phaeophyceae, Rhodophyceae and Chlorophytceae, were proven to have potentials medicinal activities such as, antibacterial, antiviral, antitumour, antifungal, antiprotozoa, and mosquito and larva control (Bansemir et al, 2006). Only certain antibacterial activities of brown seaweed species have been studied in details [evaluation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)].
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