Antibacterial activity from soft corals of the Red Sea, Saudi Arabia

Abstract

The present study aimed to screen for antibacterial activities in soft corals of the eastern Red Sea coast. Specimens of different species were surveyed, collected, preserved, extracted and assayed according to standard protocols. Bioactive materials were extracted using a dichloromethane/methanol mixture, and the activity was determined using the well diffusion and microdilution assay methods. All extracts demonstrated variable activity against marine bacteria previously isolated from the sea water (in situ near the soft corals). Among soft corals, Sarcophyton spp. and Sinularia polydactyla showed the highest activity (MIC=30–50μg/ml), while the crude extract of Xenia spp. showed the lowest activity (MIC=200–250μg/ml) against the isolated marine bacterial strains.Antibacterial activity was observed for five out of the seven soft coral extracts (72%) against two Gram-positive (Staphylococcus aureus and Bacillus spp.) bacterial pathogens, while none of the extracts inhibited Gram-negative (Escherichia coli) bacteria. The most potent (MIC=40–75μg/ml) crude extracts were obtained from S. polydactyla and Sarcophyton spp., while the crude extract of Xenia spp. was the least effective (MIC≥200μg/ml) against the tested Gram-positive bacteria. The results from the current study suggest that soft corals of the Red Sea (Yunbu, SA) are a potential source of novel antibiotics.