Antibacterial activity of extracts of marine algae from the Red Sea of Jeddah, Saudi Arabia

Abstract

In the present study, marine algae were collected from the southern coast of Jeddah, Saudi Arabia during summer and autumn 2009. The antibacterial activities of petroleum ether, diethyl ether, ethyl acetate and  methanol extracts of marine algae belonging to the Chlorophyta, Phaeophyta and Rhodophyta were studied. Their crude extracts were tested against different types of Gram-positive bacteria (Bacillus subtilis,  Methicillin-Resistant Staphylococcus aureus (MRSA) and Staphylococcus aureu) and Gram-negative bacteria  (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa). All marine algae extracts tested  exhibited a broad spectrum of antibacterial activity. The maximum inhibition activities were shown for  extracts of Padina pavonica and Turbinaria triquetra. The growth inhibitions of bacteria by Sargassum  portieriatum extracts were higher in samples collected during autumn than that investigated in summer. The  maximum inhibitory effect of Gracilaria multipartita was observed in the petroleum ether extract against B.  subtilis and E. coli. The ethyl acetate and petroleum ether extract of Enteromorpha prolifera and Ulva reticulata  showed strong activity against the tested bacteria. The tested microorganisms that were susceptible to the most effective extracts were further tested for the minimum inhibitory concentration (MIC).  The MIC of the tested microorganisms was between 0.5 and 1.25 µg/ml. The results of the present study confirmed the potential use of marine algae as a good source of antibacterial agent.

Key words: Chlorophyta, Phaeophyta, Rhodphyta, gram-positive bacteria, gram-negative bacteria,  solvent extract, minimum inhibitory concentration (MIC).