In vitro screening of antimicrobial activity of extracts of some macroalgae collected from Abu-Qir bay Alexandria, Egypt

Ethanol, methanol and acetone extracts of nine marine macroalgae (Rhodophyta, Chlorophyta and Phaeophyta) from Abu-Qir bay (Alexandria, Egypt) were evaluated for antimicrobial activity by agar well diffusion methods against pathogenic microbes (Bacillus subtilis, Staphylococcus aureus and Streptococcus aureus as gram-positive bacteria, and (Escherichia coli, Salmonella typhi and Klebsiella pneumoniae as gram-negative bacteria) and one yeast strain Candida albicans. All pathogenic microorganisms were obtained from Culture Collection of Botany Department, Faculty of Science, Tanta University. The best results were obtained by acetone extracts with inhibition activity (36.7%), followed by the methanol extracts (32.9%), and then ethanol extracts (30.2%) for all tested microorganisms. The tested species of Chlorophyta were the most active followed by Rhodophyta and Phaeophyta. The most active seaweeds was Ulva fasciata (chlorophyceae) against all tested microorganisms.