Antibacterial activities of some marine algae from the Aegean Sea (Turkey)

In this study, methanolic extracts of six marine algae belong to Rhodophyceae (Corallina officinalis), Phaeophyceae (Cystoseira barbata, Dictyota dichotoma, Halopteris filicina, Cladostephus spongiosus f. verticillatus) and Chlorophyceae (Ulva rigida) from the North Aegean Sea (Turkey) were studied for their antibacterial activity against pathogenic microbes, 3 gram positive (Staphylococcus aureus, Micrococcus luteus and Enterococcus faecalis) and 3 Gram negative (Escherichia coli, Enterobacter aerogenes and E. coli O157:H7) in vitro. Extracts of all the test marine algae except C. officinalis showed inhibition against S. aureus. On the other hand, highest inhibiton activity among all the extratcs was shown to E . aerogenes by C . officinalis. The extract from C. barbata has shown broader activity spectrum against all the test organisms.

There are some studies on antimicrobial activity of marine algae from Turkey (Haliki et al., 2005;Tuney et al., 2006Tuney et al., , 2007Ozdemir et al., 2006;Karabay-Yavasoglu et al., 2007)  for the first time for antibacterial activity from the Aegean Sea (Turkey).

Extract preparation and antibacterial assay
Collected samples were washed with tap water to remove epiphytes and other marine organisms and then washed with distilled water. Samples were dried at 45 o C and powdered. This material mixed with methanol (1:50, w/v) and placed into the soxhlet apparatus. Extraction solvent was evaporated under vacuum and used for antibacterial assay by paper disc diffusion method (El-Masry et al., 2000).
Test microorganisms were cultivated on Mueller Hinton Broth at 37 o C for 18 h before inoculation for assay. 100 µl of broth culture which contains 10 7 -10 8 number of bacteria/mL was added to Tryptic Soy Agar (Merck) medium and poured to sterile petri dishes. After medium solidified, the discs impregnated with extracts were placed onto the surface. Dishes were incubated at the same conditions mentioned above. Assays were run in triplicate. After incubation the clearence zones around the discs were measured and expressed in milimeter.

RESULTS AND DISCUSSION
Antibacterial activities of crude extracts of six marine algae from the North Aegean Sea (Turkey) were determined by paper disc diffusion method and the results are summarised in Table 1 and Figure 2. Crude extracts of all tested algae except C . officinalis showed inhibition against S. aureus and the extract of U. rigida was the most effective. On the other hand, highest inhibiton activity was shown in E. aerogenes (34.00 ± 1.00 mm) by C. officinalis and it was followed with E. coli and E. faecalis (Figures 2 and 3). D. dichotoma has the Studies that were carried on antimicrobial activity of some algae from the different parts of the world are summarized in Table 2. Many marine algae were screened for their antimicrobial activity by Reichelt and Borowitzka (1984) and Salvador et al. (2007). Salvador et al. (2007) studied antimicrobial activities of 82 marine algae as fresh and lyophilized forms. It was reported that the members of the red algal order, Bonnemaisoniales were the most active. In this study , they also studied with C. spongiosus f. verticillatus, C. barbata, D. dichotoma and U. rigida, as the same taxa that we used and inhibitor activities of these algae species against S. aureus ATCC 29213 were 14.1, 18 and 12.3 mm in diameter, respectively. They have also reported any inhibitor activitiy was obtained by U. rigida. Tuney et al. (2007) used fresh and dried materials of U . rigida for the extraction. They found that while dried samples had no activity against S. Aureus, the extract prepared from fresh material has shown remarkably inhibitor activity to same strain. They have also obtained inhibitor activity against E. faecalis and E. coli. Karabay-Yavasoglu et al. (2007) reported that the only methanolic and chloroform-prepared extracts of Jania rubens (Corallinales) have significant antimicrobial activitiy, however volatile oil did not inhibit significantly test microorganisms. Ozdemir et al. (2006) indicated that the volatile oils of D. membranacea and C. barbata did not remarkably inhibit test organisms and the methanolic extracts of both algae have shown lower inhibitor activitiy than the hexane extracts. Bansemir et al. (2006) have investigated the antibacterial activities of the extracts from 26 algae species prepared by dichlorometane, methanol and water against five fish-pathogenic bacteria. The highest activities were obtained by the dichloromethane prepared extracts. They have reported that the most active algal species was Asparagopsis armata against all tested bacteria. Ely et al. (2004) have shown the methanolic extract of Cladophora prolifera had moderate bactericidal activity against S. aureus and Vibrio cholerea. Freile-Pelegrin and Morales (2004) studied ethanolic extracts from different thallus regions (apical, basal and stolon) of Caulerpa spp. They indicated that the stolon was the region having the highest antibacterial activity.

Conclusion
C . officinalis and C . spongiosus f. verticillatus were studied for the first time for antibacterial activity from the Aegean Sea (Turkey). Methanolic extract of C. officinalis showed good activity against E. aerogenes, E. coli and E. faecalis. The growth of food-borne pathogen E. coli O157:H7 was inhibited by the extract of C. barbata with the strong inhibition level (22.33 ± 0.57 mm) and as far as we know this strain was not used before as test organisms. It was indicated before that methanolic extract of C. barbata had no antibacterial activity against E. coli by other authors (Ozdemir et al., 2006;Salvador et al., 2007) but in this study our extract inhibited in diameter of 11.66 ± 1.15 mm.