Locational and organic solvent variation in antimicrobial activities of crude extracts of marine algae from the coast of Izmir (Turkey)

During this research, a total of 98 extracts from 13 algal species were tested in vitro for antimicrobial activities of algae against Candida sp., Enterococcus faecalis, Staphylococcus aureus, Streptococcus epidermidis, Pseudomonas aeruginosa and Escherichia coli using the disc diffusion method. The ability of algae to perform antibacterial and antifungal activity was investigated at three different localities. Cystoseira mediterranea and Ulva rigida were the only algae found in all three sites, and contamination was detected in algae collected from sites I and 3, with antibacterial capacity being highest in those from site 1, where samples were collected during red tide. Extractions were performed with four different solvents - ethanol, methanol, acetone and diethyl ether. In particular, diethyl ether extracts of fresh C mediterranea, Enteromorpha linza, U. rigida, Gracilaria gracilis and Ectocarpus siliculosus appeared to yield better results than those of methanol, ethanol and acetone. However, diethyl ether extracts of some species, such as Padina pavonica, Colpomenia sniosa, Dictyota linearis, Dictyopteris membranacea, Ceramium rubrum, and Acanthophora nojadiformis, gave different results. Methanol extracts of A. nojadiformis showed effective antibacterial activity against P. aeruginosa, and methanol extracts of C rubrum showed antifungal and antibacterial activity against Candida sp., E. coli, and P. aeruginosa. Acetone extracts of Hypnea sp. showed antibacterial activity against P. aeruginosa, and ethanol extract of Cladophora sp. against E. faecalis only. Some of the collected samples were dried and extracts of fresh and dry samples were compared. Although fresh extracts of G. gracilis and E. siliculosus inhibited the tested microorganisms from populating, their dried extracts had no effect on gram-negative and positive bacteria.