Global Journal of Pharmacology 8 (2): 268-274, 2014 ISSN 1992-0075 © IDOSI Publications, 2014 DOI: 10.5829/idosi.gjp.2014.8.2.83254 Corresponding Author: K. Kolanjinathan, Division of Microbiology, Faculty of Science, Annamalai University, Annamalai Nagar - 608 002, India. 268 Pharmacological Efficacy of Marine Seaweed Gracilaria edulis Extracts Against Clinical Pathogens K. Kolanjinathan and P. Saranraj Division of Microbiology, Faculty of Science, Annamalai University, Annamalai Nagar – 608 002, India Abstract: Seaweeds are the eukaryotic organisms that lives in salty water in the ocean and is recognized as a potential source of bioactive natural products. The present study was conducted to screen the pharmacological activity of Gracilaria edulis solvent extracts against human pathogenic bacteria and fungi. The seaweed Gracilaria edulis was extracted using the organic solvents viz., methanol, acetone, petroleum ether, hexane and ethanol. Antimicrobial activity of Gracilaria edulis solvent extract was determined by Disc diffusion method. Among the solvents tested, methanol extract of Gracilaria edulis showed maximum inhibitory activity than other solvents. The zone of inhibition of Gracilaria edulis methanol extract against bacteria was maximum against Gram positive cocci Streptococcus pyogenes followed by Bacillus subtilis, Staphylococcus aureus, Streptococcus epidermis and Bacillus cereus. For Gram negative bacteria, the maximum zone of inhibition was recorded in methanol extract of Gracilaria edulis against Klebsiella pneumoniae followed by Enterobacter aerogens, Salmonella typhi, Pseudomonas aeruginosa, Escherichia coli and Vibrio cholerae. For fungi, the zone of inhibition was maximum against Aspergillus flavus followed by Aspergillus fumigatus, Aspergillus niger, Candida albicans, Candida glabrata and Saccharomyces cerevisiae. Key words: Gracilaria edulis Solvent Extracts Antimicrobial Activity Bacteria And Fungi INTRODUCTION Seaweeds have been traditionally used in human and Marine organisms are source material for structurally compounds such as carotenoids, dietary fiber, protein, unique natural products with pharmacological and essential fatty acids, vitamins and minerals [5]. Important biological activities. Among the marine organisms, the polysaccharides such as agar, alginates and carrageenans macroalgae occupy an important place as a source of obtained from seaweeds are used in pharmaceutical as biomedical compounds [1]. About 2400 natural products well as in the food industries. Seaweeds provide a rich have been isolated from macroalgae belonging to the source of structurally diverse and biologically active classes Rhodophyceae, Phaeophyceae and secondary metabolites. The functions of these secondary Chlorophyceae. The antimicrobial activity was regarded metabolites are defense mechanism against herbivores, as an indicator to detect the potent pharmaceutical fouling organisms and pathogens chemical defense capacity of macroalgae for its synthesis of bioactive mechanisms against herbivore; for example, grazer- secondary metabolites. The compounds derived from induced mechanical damage triggers the production of macroalgae are reported to have broad range of biological chemicals that acts as feeding detergents or toxins in activities such as antibacterial [2], anticoagulant [3] and seaweeds [6]. antifouling activity [4]. The antimicrobial agents such as Marine organisms are a rich source of structurally Chlorellin derivatives, acrylin acid, halogenated aliphatic novel and biologically active metabolites. Secondary or compounds, phenolic inhibitors and more recently primary metabolites produced by these organisms may Guaiane sesquiterpenes and labdane diterpernoids were be potential bioactive compounds of interest in the also detected from macroalgae [2]. pharmaceutical industry. To date, many chemically unique animal nutrition. Seaweeds are rich source of bioactive