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DOI: 10.1055/s-0029-1234821
Antibacterial activity of the green alga Ulva rigida collected from Tunisian coast: seasonal and geographical variation
Ulva rigida is one of the most abundant algae in Tunisia with important blooms particularly in warm seasons [1]. We therefore investigated the antibacterial activity of extracts of this alga collected at different seasons and from two different locations: the coastal area of Cap Zebib and the Ghar el Melh lagoon.
Antibacterial activity of Ulva rigida organic extracts was assayed against both Gram-positive and Gram-negative bacteria. Tests were performed by the diffusion method [2].
The crude extracts of Ulva rigida collected in summer were more effective than those of the other seasons. The strongest antibacterial activity was obtained by samples collected from the lagoon. Two gram positive bacteria: S.aureus and Streptococcus sp. were found to be the most sensitive strains to algal extracts.
The bioassay guided fractionation of the dichloromethane/methanol extract for Ulva rigida collected in summer from the lagoon, showed at least two different compounds with an antibacterial activity observed for the non polar fractions (eluted with 100% CH2Cl2 and 95/5 CH2Cl2/MeOH) and another one for moderately polar fraction (85/15 CH2Cl2/MeOH).
These results highlighted a variable antibacterial activity of Ulva rigida related to the bacterial strain, the season of harvest and the geographic location. Previous study on this alga collected from Tunisian coast did not report any significant antibacterial activity [3]. Thereby Ulva rigida collected from Ghar El Melh lagoon should be considered as a valuable source, especially for antibacterial activity against pathogenic bacteria.
References: [1] Shili, A. et al. (2000)J. Cost. Conserv. 8:127–134.
[2] Rios, J.L. et al. (1988)J. Ethnopharmacol. 23:127–149.
[3] Ktari, L. et al. (2001)J. Rech. Oceanogr. 26:37–41.