Infectious diseases remain one of the leading causes of death due to antibiotic resistant microorganisms. The frequency of resistance in microbial pathogens continues to grow at an alarming rate throughout the world (Schmitz et al., 1999). Decreased efficacy and resistance of pathogens to antibiotics has necessitated development of new alternatives (Ravikumar et al., 2010). To overcome these problems, the development of effective newer drugs without any side effects is an urgent need. In general, marine plants such as mangroves, seaweeds, sea grasses and marines sponges are extensively studied for antiviral, antiplasmodial, antibacterial, antifungal, hepatoprotective, anti-ulcer properties (Ravikumar et al., 2009&2011).
Medicinal plant is plant containing substance which can be used for the medication or become precursor of drug synthesis (Sofowora, 1982). Medicinal plant has been source of human health since ancient time, whereas about 60-75% of world populations require plant for carrying health (Farnsworth, 1994; Joy et al., 1998 and Harvey, 2000). Plants and microbes are the main source of natural products (Hayashi et al., 1997; Armaka et al., 1999; Lin et al., 1999a &b and Basso et al., 2005), and consistently become main source of the newest drugs (Harvey, 2000). The drug development from natural sources are based on the bioassay-guided isolation of natural products, due to the traditional uses of local plants (ethnobotanical and ethanopharmacological applications) (Atta-ur-Rahman and Choudhary, 1999).
Seagrasses are submerged marine angiosperms growing abundantly in tidal and sub tidal areas of all seas except in the Polar Regions. Sea grass biomass is used as human food especially by coastal populations (Hemminga and Duarte, 2000). In folk medicine, seagrasses have been used for a variety of remedial purposes, like, fever, skin diseases, muscle pains, wounds and stomach problems etc. (de la Torre-Castro and Rönnbäck, 2004). In India, seagrasses were used as medicine (treatment of heart conditions, seasickness), food (nutritious seeds), fertilizer (nutrient rich biomass) and livestock feed (goats and sheep) (Newmaster et al., 2011). Seeds of Enhalus acoroides are thought to have aphrodisiac and contraceptive properties (Aliño et al., 1990). (12)
Numerous seagrasses have been shown to have antibacterial activities. Halophila stipulacea,Cymodocea serrulata and Halodule pinifolia (Kannan et al., 2010a), Enhalus acoroides (Qi et al., 2008) and Enhalus acoroides, Thalassiahemprichii, Halodule pinifolia, Syringodium isoetifolium, and Cymodocea rotundata have been reported to exhibit antibacterial activity (Kannan et al., 2013). Moreover, preliminary data suggest that seagrasesses could represent an interesting source of antilarvacidal (Ali et al., 2013) and antioxidant (Ramah et al., 2014)
In recent years, development of multidrug resistance in the pathogenic bacteria and parasites has created major clinical problems in the treatment of infectious diseases (Ravikumar et al., 2010a). There have been a number of reports that demonstrating the antimicrobial activity of seaweeds, mangroves and other marine forms and only limited information were available from the seagrasses of the corners of the world and even very mere information available from India. The aim of this study is to evaluate and compare the ability of seagrass extracts to produce bioactive compounds of potential therapeutic interest. Antimicrobial activities found in seagrass was considered to be an indication of synthesis of bioactive secondary metabolites (Kannan et al., 2010a).
The antibacterial activity of five different leaves extracts of H. uninervis against seven bacterial pathogens strains were effective. Among them, ethanol extract was the more effective against P. aeruginosa than other extracts, this showed that ethanol is suitable for extracting active compounds from seagrass. This investigation were supported the earlier reports thus, the methanolic extract of Enhalus acoroides were effective against P. aeruginosa, K. pneumoniaeand S. aureus than hexane extract (Alam et al., 1994). The ethanolic extract in this study showed the best activity against pathogenic bacteria and this present findings is consistent with some earlier reports (Umamaheshwari et al., 2009) and it showed that ethanol and methanol extractions of the seagrasses Halophila ovalisand Halodule pinafolia showed better zone of inhibition against bacterial pathogens that other tested extracts.
In our present finding Gram-negative bacteria was more sensitive than Gram-positive bacteria. This results in agreement with the finding that the antifouling of some marine organisms against Bacillus and Pseudomonas sp. was reported (Bhosale et al., 2002), regarding the acetone extract our results coincide with the report of acetone extract of Halophila ovalis and Zostera capensis which showed less activity compared to the other solvents (Sreenath Kumar et al., 2008). The variation of antibacterial activity of the extracts might be due to distribution of antimicrobial substances, which varied from species to species (Lustigman and Brown, 1991).
The difference further observed in the antimicrobial effect of the sea grass extracts studied against both gram positive and gram negative bacteria in the present studymay be due to differences in permeability barriers. In gram negative species outer membrane is fairly effect barrier for the extract and also active compounds persist in the sea grass (Ravikumar et al., 2009). The more susceptibility of gram positive bacteria to the sea grass extract was due to the differences in their cell wall structure and their composition (Tortora et al., 2001). In gram negative bacteria the outer membrane act as barrier to many environmental substances including antibiotics (Kandhasamy and Arunachalam, 2008).
The ethyl acetate extract of H. uninervis had lowest activity and this can be correlated with the results of (Sreenath Kumar et al., 2008) who reported that the ethyl acetate extracts of H. ovalis was active against the tested pathogens namely Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, Salmonella typhimurium and Micrococcus luteus.
The results indicated that the aqueous extracts have lightly activity only against P. aeruginosa than other tested bacterial pathogens. This results in agreement with the finding that the water extract showed no activity against any of the tested organisms. Aqueous and ethanol extract of Heracleum Sphondylium showed antimicrobial activities against Gram-positive and Gram-negative bacteria, (Ergene et al., 2006).
Also because of the reported study of phytochemical analysis of Hexane, Chloroform, Ethyl acetate, Ethanol and Aqueous extracts of three glycosides have saponins, and tannins. Sugars and quinine were absent in all the three seagrasses (Cymodocea serrulata, Halophila ovalis and Halodule pinifolia) (Sangeetha and Asokan, 2016). The earlier reports like Ergene et al., 2006 who revealed the presence of tannins, saponins, proteins, resins, reducing sugar, acidic compounds, alkaloids, cardiac glycosides and terpenoids in the phytochemical analysis of C. rotundata. The phytochemical compounds viz., glycoside, saponins, tannins, flavonoids, terpenoides and alkaloids have antimicrobial activity (Okeke et al., 2001).