Marine macroalgae as a potential source of bioactive natural products with antibacterial activity

The present investigation aimed to evaluate the antibacterial activity of marine macroalgae collected during winter and spring 2011 from the Red Sea of Jeddah, Saudi Arabia. The activity of petroleum ether, diethyl ether, ethyl acetate and methanol extract of algae belonging to Chlorophyta, Phaeophyta and Rhodophyta were examined against pathogenic bacteria. The crude extract of algae evoked several patterns of antibacterial activities. The petroleum ether extract of Gracilaria multipartita, Ulva reticulata and Sargassum marginatum collected in spring recorded the maximum inhibitory activity against Bacillus subtilis (14–25 mm), MRSA (24–35 mm) and Staphylococcus aureus (14–18 mm), respectively. However, Escherichia coli, Klebsiella pneumoniae were highly inhibited by petroleum ether extract of G. multipartita collected in spring (17–24 mm and 15–19 mm, respectively). Pseudomonas aeruginosa recorded the greatest zone of inhibition (18–22 mm) by the petroleum ether extract of S. marginatum gathered during winter. The MICs values for bacteria were ranged between 1.00–2.75 μg/ml. The chemical composition of the most effective algae extract against pathogenic bacteria was performed by GC-MS and ¹H-NMR analysis. The major components of extract were hydrocarbons, carotene derivatives, fatty acids and sterols. The present finding revealed that the tested algae can be used as possible natural source of antibacterial compounds.