Antibacterial activities of the methanol extract, fractions and compounds from Elaeophorbia drupifera (Thonn.) Stapf. (Euphorbiaceae)

Abstract

Background: Elaeophorbia drupifera (Thonn.) Stapf. (Euphorbiaceae) is used in Cameroonian folk medicine to treat several ailments including bacterial-related diseases such as skin infections. In this study, the methanol extract from the leaves (EDL), fractions (EDLa-d), sub-fractions EDLc1-7 and EDLc31-35 as well as isolated compounds were tested for their antimicrobial activities against a panel of Gram-negative and Gram-positive bacteria including multidrug resistant (MDR) phenotypes. Methods: The broth microdilution method was used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the above samples; column chromatography was used for the fractionation and purification of the leaves extract whilst the chemical structures of compounds were determined using spectroscopic techniques. Results: Phytochemical investigation lead to the isolation of a mixture (1: 3) of stigmasterol and beta-sitosterol (1 + 2), euphol (3), sitosterol-O-beta-D-xylopyranoside (4), 3,3', 4'-tri-O-methylellagic acid (5), a mixture (1: 1) of afzelin and quercetin-3-O-beta-D-xylopyranoside (6 + 7), 3,3', 4'-tri-O-methylellagic acid 4-O-beta-D-glucopyranoside (8), ellagic acid-4-O-beta- xylopyranoside-3,3', 4'-trimethyl ether (9) from EDLc. Crude extract and fractions displayed selective activities with MIC values ranged from 32 to 1024 mu g/mL for EDL against 84.9% of the 33 tested bacteria, 93.9% for EDLc, 69.7% for EDLb, 33.4% for EDLa and 0.03% for EDLd. MIC values ranged from 16 to 1024 mu g/mL were obtained with EDLc3 and EDLc4 on all tested bacteria meanwhile other sub-fractions displayed selective activities. MIC value of 32 mu g/mL was obtained with fractions EDLa against Escherichia coli AG100, EDLc against Enterobacer aerogenes ATCC13048 and EA298. For sub-fractions obtained from EDLc, the lowest MIC value of 16 mu g/mL was recorded with EDLc3 against Staphylococcus aureus MRSA11. A corresponding value of 8 mu g/mL against Providencia stuartii NAE16 was recorded with EDLc33 obtained from further fractionation of EDLc3. EDLc3 had MIC values below 100 mu g/mL against all tested bacteria. Compound 5 as well as the mixture (1: 1) of 6 and 7 inhibited the growth of all the tested bacteria with MICs ranged from 64 to 256 mu g/mL. Conclusion: Elaeophorbia drupifera is a potential source of phytomedicine to tackle MDR bacteria. Sub-fraction EDLc3 was more active than all isolated compounds and deserves further investigations to develop natural drug to combat Gram-negative, Gram-positive bacteria and otherwise MDR phenotypes.