title: The anti-Staphylococcus aureus activity of the phenanthrene fraction from fibrous roots of Bletilla striata.
abstract: BACKGROUND
  Bletillae 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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  EF60 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 IC50of 75 μg/mL.
  
  
  CONCLUSIONS
  Our studies indicated that EF60 is worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by S. aureus and MRSA.
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.|Shaoxing Central Hospital, Shaoxing, Zhejiang Province, China.
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Guo
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.
authors.forename: Bin-Ling
authors.initials: BL
authors.lastname: Dai
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.
authors.forename: Ni-Pi
authors.initials: NP
authors.lastname: Chen
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.
authors.forename: Li-Xia
authors.initials: LX
authors.lastname: Jin
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.
authors.forename: Fu-Sheng
authors.initials: FS
authors.lastname: Jiang
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China.
authors.forename: Zhi-Shan
authors.initials: ZS
authors.lastname: Ding
authors.affiliation: Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China. qian201@163.com.
authors.forename: Chao-Dong
authors.initials: CD
authors.lastname: Qian
mesh_terms: D000900:Anti-Bacterial Agents / Q000302:isolation & purification* / Q000494:pharmacology / Q000633:toxicity; D003603:Cytotoxins / Q000494:pharmacology; D004365:Drugs, Chinese Herbal / Q000494:pharmacology* / Q000633:toxicity; D006461:Hemolysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D029595:Orchidaceae / Q000737:chemistry* / Q000633:toxicity; D010616:Phenanthrenes / Q000302:isolation & purification* / Q000494:pharmacology / Q000633:toxicity; D018517:Plant Roots / Q000737:chemistry; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D003603:Cytotoxins; D004365:Drugs, Chinese Herbal; D010616:Phenanthrenes; C031181:phenanthrene
keywords: Antibacterial; Bletillae Rhizom; Gram-positive bacteria; Postantibiotic effect; Time-kill assays