Antimicrobial active compounds of green alga Ulva rigida collected from Ghar El Melh lagoon (North of Tunisia)

The green alga Ulva rigida is wellspread within Tunisian coast mainly in the northern region of Ghar El Melh lagoon with important blooms particularly in warm seasons [1]. The aim of this study is to evaluate its antimicrobial potential against pathogens bacteria and fungi.

Thus, polar and non polar organic crude extracts of dried Ulva rigida collected from Ghar El Melh lagoon (37° 10.8' N, 10° 16.8' E), were tested against eighteen pathogenic species of bacteria and the yeast Candida albicans. The dichloromethane/methanol extract which exhibited the most significant activity was therefore subjected to column gradient chromatography on silica gel and led to one hundred thirty seven fractions. Eluates were subsequently grouped into twenty nine sub-fractions based on their similarity in Thin Layer Chromatography (TLC). According to TLC visualisation by phosphomolybdic acid and Libermann's spraying, and UV examination, we retained sub-fractions considered of further interest, to isolate antibacterial compounds through bioassay-guided fractionations. Purification processes (column chromatography with Silica gel and Sephadex LH-20 and preparative TLC) of the most active fractions led to purified and semi purified compounds with strong antibacterial activity especially against Staphylococcus aureus and Micrococcus sp. which are recognized amongst most common human pathogens. Nevertheless, active compounds showed weak value of CMI. 1H NMR and 13C NMR provided structural information about active compounds.

References: 1- Shili A et al. (2000) Journal of Costal Conservation 8: 127–134.