Abstract
BackgroundBletillae Rhizoma, the tuber of Bletilla striata, has been used in Chinese traditional medicine to treat infectious diseases. Chemical studies indicated that phenanthrene was one of the most important components of the herb, with a broad spectrum of antibiotic activity against Gram-positive bacteria. The objective of this study was to further characterize the antibacterial activity of the phenanthrene fraction from the fibrous root of the pseudobulb of B. striata.MethodsThe phenanthrene fraction (EF60) from the ethanol extract of fibrous roots of Bletilla striata pseudobulbs was isolated using polyamide column chromatography. The antibacterial activity of the fraction was evaluated in vitro using a 96-well microtiter plate and microbroth dilution method. The cytotoxicity of EF60 against mammalian cells was tested by hemolysis and MTT assays.ResultsEF60 was obtained using alcohol extraction and polyamide column chromatography, with a yield of 14.9 g per 1 kg of the fibrous roots of B. striata. In vitro tests indicated that EF60 was active against all tested strains of Staphylococcus aureus, including clinical isolates and methicillin-resistant S. aureus (MRSA). The minimum inhibitory concentration (MIC) values of EF60 against these pathogens ranged from 8 to 64 μg/mL. Minimum bactericidal concentration tests demonstrated that EF60 was bactericidal against S. aureus 3304 and ATCC 29213 and was bacteriostatic against S. aureus 3211, ATCC 25923, and ATCC 43300. Consistently, the time-kill assay indicated that EF60 could completely kill S. aureus ATCC 29213 at 2× the MIC within 3 h but could kill less than two logarithmic units of ATCC 43300, even at 4× the MIC within 24 h. The postantibiotic effects (PAE) of EF60 (4× MIC) against strains 29213 and 43300 were 2.0 and 0.38 h, respectively. Further studies indicated that EF60 (160 μg/mL) showed no cytotoxicity against human erythrocytes, and was minimally toxic to Human Umbilical Vein Endothelial Cells with an IC50 of 75 μg/mL.ConclusionsOur studies indicated that EF60 is worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by S. aureus and MRSA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-016-1488-z) contains supplementary material, which is available to authorized users.
Highlights
Bletillae Rhizoma, the tuber of Bletilla striata, has been used in Chinese traditional medicine to treat infectious diseases
Previous investigations on the constituents of Bletillae Rhizoma have revealed the presence of monomeric phenanthrene, dimeric phenanthrenes, and their derivatives, which contain a potent antibacterial activity against Gram-positive bacteria [12,13,14]
Isolation of phenanthrene fractions from the fibrous roots of B. striata To obtain phenanthrene fractions, ethanol extract from the fibrous roots of B. striata was loaded onto a polyamide resin column and eluted using step-gradient ethanol in water to generate five fractions, namely EF20, EF40, EF60, EF80, and EF95
Summary
Bletillae Rhizoma, the tuber of Bletilla striata, has been used in Chinese traditional medicine to treat infectious diseases. The objective of this study was to further characterize the antibacterial activity of the phenanthrene fraction from the fibrous root of the pseudobulb of B. striata. Previous investigations on the constituents of Bletillae Rhizoma have revealed the presence of monomeric phenanthrene, dimeric phenanthrenes, and their derivatives, which contain a potent antibacterial activity against Gram-positive bacteria [12,13,14]. A large number of phenanthrenes have been isolated from Bletillae Rhizoma and have been demonstrated to possess antimicrobial activities, further pharmacological studies of these compounds are limited due to low content of phenanthrenes in the pseudobulbs of B. striata
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