In vitro antimicrobial activity of crude extracts and isolated constituents of Alternanthera maritima

Abstract

The antimicrobial activity of ethanolic extracts (aerial parts and roots), fractions and isolated compounds of Alternanthera maritima (Mart.) St. Hil. (Amaranthaceae) were evaluated against microorganisms involved in human infections. These bioassays were conducted using thirty strains including Gram-positive and Gram-negative bacteria, yeasts and dermatophytes. The minimum inhibitory concentrations (MIC) values for isolated constituents varied from 25 to 500 μg/ml. Bioassay-guided fractionation, purification and isolation were performed by chromatographic methods and the structures of isolated compounds were established by analysis of chemical and spectral evidences (UV, IR, NMR and ES-MS). The following bioactive compounds were isolated: steroids (stigmasterol 1, β-sitosterol 2, campesterol 3, spinasterol 4 and Δ7 stigmastenol 5), organic acids (palmitic 6 and vanillic 13 acids), saponins (stigmasterol 7 and Δ7 stigmastenol-3-O-β-D- glucopyranosides 8, β-sitosterol 9 and spinasterol-3-O-α-D- glucopyranosides 10), flavonoid aglycones (quercetin 3-methyl ether 11 and kaempferol 12) and flavonoid glycosides (vitexin 14, isovitexin 15, isorhamnetin-3-O-robinobioside 16 and quercetin-3-O-rutinoside 17). The results were analyzed statistically by cluster analysis and principal components analysis.